How to break out of multiple loops

Question

Given the following code  that doesn t work    while True       snip  print out current state     while True          ok   get input  Is this ok   y n            if ok lower       y   break 2  this doesn t work            if ok lower       n   break      do more processing with menus and stuff   Is there a way to make this work  Or do I have do one check to break out of the input loop  then another  more limited  check in the outside loop to break out all together if the user is satisfied

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this version breaks up to a certain label  break label   None while True        snip  print out current state     while True          ok   get input  Is this ok   y n            if ok     y  or ok     Y               break label    outer      specify label to break to             break         if ok     n  or ok     N               break     if break label          if break label     inner               break                     propagate up         break label   None            we have arrived  if break label      if break label     outer           break                         propagate up     break label   None                we have arrived    do more processing with menus and stuff

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In this case  as pointed out by others as well  functional decomposition is the way to go  Code in Python 3   def user confirms        while True          answer   input  Is this OK   y n     strip   lower           if answer in  yn               return answer     y   def main        while True            do stuff         if user confirms                break

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To break out of multiple nested loops  without refactoring into a function  make use of a  simulated goto statement  with the built-in StopIteration exception   try      for outer in range 100           for inner in range 100               if break early                    raise StopIteration  except StopIteration  pass   See this discussion on the use of goto statements for breaking out of nested loops

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Try using an infinite generator   from itertools import repeat inputs    get input  Is this ok   y n    for   in repeat None   response    i lower     y  for i in inputs if i lower   in   y    n     while True       snip  print out current state     if next response           break      do more processing with menus and stuff

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And why not to keep looping if two conditions are true  I think this is a more pythonic way   dejaVu   True  while dejaVu      while True          ok   raw input  Is this ok   y n            if ok     y  or ok     Y  or ok     n  or ok     N               dejaVu   False             break   Isn t it   All the best

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Factor your loop logic into an iterator that yields the loop variables and returns when done -- here is a simple one that lays out images in rows columns until we re out of images or out of places to put them   def it rows  cols  images       i   0     for r in xrange rows           for c in xrange cols               if i  gt   len images                   return             yield r  c  images i              i    1   for r  c  image in it rows 4  cols 4  images   a jpg    b jpg    c jpg             do something with r  c  image       This has the advantage of splitting up the complicated loop logic and the processing

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Solutions in 2 Ways  With an example  Are these two matrices equal same   matrix1 and matrix2 are same size  n  2 dimentional matrices   First Solution  without a function   same matrices   True inner loop broken once   False n   len matrix1   for i in range n       for j in range n            if matrix1 i  j     matrix2 i  j               same matrices   False             inner loop broken once   True             break      if inner loop broken once          break     Second Solution  with a function  This is the final solution for my case   def are two matrices the same  matrix1  matrix2       n   len matrix1      for i in range n           for j in range n               if matrix1 i  j     matrix2 i  j                   return False     return True   Have a nice day

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Hopefully this helps   x   True y   True while x    True      while y    True           ok   get input  Is this ok   y n              if ok     y  or ok     Y                x y   False False  breaks from both loops          if ok     n  or ok     N                 break  breaks from just one

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First  you may also consider making the process of getting and validating the input a function  within that function  you can just return the value if its correct  and keep spinning in the while loop if not   This essentially obviates the problem you solved  and can usually be applied in the more general case  breaking out of multiple loops    If you absolutely must keep this structure in your code  and really don t want to deal with bookkeeping booleans     You may also use goto in the following way  using an April Fools module from here     import the stuff from goto import goto  label  while True       snip  print out current state     while True          ok   get input  Is this ok   y n            if ok     y  or ok     Y   goto  breakall         if ok     n  or ok     N   break      do more processing with menus and stuff label  breakall   I know  I know   thou shalt not use goto  and all that  but it works well in strange cases like this

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An easy way to turn multiple loops into a single  breakable loop is to use numpy ndindex  for i in range n     for j in range n       val   x i  j      break   still inside the outer loop   for i  j in np ndindex n  n     val   x i  j    break   you left the only loop there was    You do have to index into your objects  as opposed to being able to iterate through the values explicitly  but at least in simple cases it seems to be approximately 2-20 times simpler than most of the answers suggested

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My first instinct would be to refactor the nested loop into a function and use return to break out

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You can define a variable  for example break statement    then change it to a different value when two-break condition occurs and use it in if statement to break from second loop also       while True      break statement 0     while True          ok   raw input  Is this ok   y n            if ok     n  or ok     N                break         if ok     y  or ok     Y                break statement 1             break     if break statement  1          break

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First  ordinary logic is helpful     If  for some reason  the terminating conditions can t be worked out  exceptions are a fall-back plan     class GetOutOfLoop  Exception        pass  try      done  False     while not done          isok  False         while not  done or isok               ok   get input  Is this ok   y n                if ok in   y    Y   or ok in   n    N                      done  True   probably better                 raise GetOutOfLoop           other stuff except GetOutOfLoop      pass   For this specific example  an exception may not be necessary     On other other hand  we often have  Y    N  and  Q  options in character-mode applications   For the  Q  option  we want an immediate exit   That s more exceptional

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keeplooping True while keeplooping       Do Stuff     while keeplooping             do some other stuff           if finisheddoingstuff                   keeplooping False  or something like that  You could set a variable in the inner loop  and check it in the outer loop immediately after the inner loop exits  breaking if appropriate  I kinda like the GOTO method  provided you don t mind using an April Fool s joke module - its not Pythonic  but it does make sense

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By using a function   def myloop        for i in range 1 6 1      1st loop         print  i   i          for j in range 1 11 2      2nd loop             print     i  j    i  j              for k in range 1 21 4      3rd loop                 print        i j k    i j k                  if i 3  0 and j 3  0 and k 3  0                      return    getting out of all loops  myloop     Try running the above codes by commenting out the return as well   Without using any function   done   False for i in range 1 6 1      1st loop     print  i    i      for j in range 1 11 2      2nd loop         print     i  j    i  j          for k in range 1 21 4      3rd loop             print        i j k    i j k              if i 3  0 and j 3  0 and k 3  0                  done   True                 break    breaking from 3rd loop         if done  break   breaking from 2nd loop     if done  break       breaking from 1st loop   Now  run the above codes as is first and then try running by commenting out each line containing break one at a time from the bottom

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By using a function   def myloop        for i in range 1 6 1      1st loop         print  i   i          for j in range 1 11 2      2nd loop             print     i  j    i  j              for k in range 1 21 4      3rd loop                 print        i j k    i j k                  if i 3  0 and j 3  0 and k 3  0                      return    getting out of all loops  myloop     Try running the above codes by commenting out the return as well   Without using any function   done   False for i in range 1 6 1      1st loop     print  i    i      for j in range 1 11 2      2nd loop         print     i  j    i  j          for k in range 1 21 4      3rd loop             print        i j k    i j k              if i 3  0 and j 3  0 and k 3  0                  done   True                 break    breaking from 3rd loop         if done  break   breaking from 2nd loop     if done  break       breaking from 1st loop   Now  run the above codes as is first and then try running by commenting out each line containing break one at a time from the bottom

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Since this question has become a standard question for breaking into a particular loop  I would like to give my answer with example using Exception    Although there exists no label named breaking of loop in multipally looped construct  we can make use of User-defined Exceptions to break into a particular loop of our choice  Consider the following example where let us print all numbers upto 4 digits in base-6 numbering system    class BreakLoop Exception       def   init   self  counter           Exception   init   self   Exception 1           self counter   counter  for counter1 in range 6       Make it 1000     try          thousand   counter1   1000         for counter2 in range 6      Make it 100             try                  hundred   counter2   100                 for counter3 in range 6     Make it 10                     try                          ten   counter3   10                         for counter4 in range 6                               try                                  unit   counter4                                 value   thousand   hundred   ten   unit                                 if unit    4                                       raise BreakLoop 4    Don t break from loop                                 if ten    30                                       raise BreakLoop 3    Break into loop 3                                 if hundred    500                                      raise BreakLoop 2    Break into loop 2                                 if thousand    2000                                      raise BreakLoop 1    Break into loop 1                                  print    04d   format value                               except BreakLoop as bl                                  if bl counter    4                                      raise bl                     except BreakLoop as bl                          if bl counter    3                              raise bl             except BreakLoop as bl                  if bl counter    2                      raise bl     except BreakLoop as bl          pass   When we print the output  we will never get any value whose unit place is with 4  In that case  we don t break from any loop as BreakLoop 4  is raised and caught in same loop  Similarly  whenever ten place is having 3  we break into third loop using BreakLoop 3   Whenever hundred place is having 5  we break into second loop using BreakLoop 2  and whenver the thousand place is having 2  we break into first loop using BreakLoop 1    In short  raise your Exception  in-built or user defined  in the inner loops  and catch it in the loop from where you want to resume your control to  If you want to break from all loops  catch the Exception outside all the loops   I have not shown this case in example

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keeplooping True while keeplooping       Do Stuff     while keeplooping             do some other stuff           if finisheddoingstuff                   keeplooping False  or something like that  You could set a variable in the inner loop  and check it in the outer loop immediately after the inner loop exits  breaking if appropriate  I kinda like the GOTO method  provided you don t mind using an April Fool s joke module - its not Pythonic  but it does make sense

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I d like to remind you that functions in Python can be created right in the middle of the code and can access the surrounding variables transparently for reading and with nonlocal or global declaration for writing   So you can use a function as a  breakable control structure   defining a place you want to return to   def is prime number        foo   bar   number      def return here            nonlocal foo  bar         init bar   bar         while foo  gt  0              bar   init bar             while bar  gt   foo                  if foo bar    number                      return                 bar -  1             foo -  1      return here        if foo    1          print number   is prime       else          print number       bar       foo       gt  gt  gt  is prime 67  67 is prime  gt  gt  gt  is prime 117  117   13   9  gt  gt  gt  is prime 16  16   4   4

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My first instinct would be to refactor the nested loop into a function and use return to break out

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This isn t the prettiest way to do it  but in my opinion  it s the best way  def loop        while True       snip  print out current state         while True              ok   get input  quot Is this ok   y n  quot               if ok     quot y quot  or ok     quot Y quot   return             if ok     quot n quot  or ok     quot N quot   break          do more processing with menus and stuff  I m pretty sure you could work out something using recursion here as well  but I don t know if that s a good option for you

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The way I solve this is by defining a variable that is referenced to determine if you break to the next level or not  In this example  this variable is called  shouldbreak    Variable That Counts To Three 1 while 1  1      shouldbreak  no      Variable That Counts To Five 0     while 2  2          Variable That Counts To Five  1         print Variable That Counts To Five          if Variable That Counts To Five    5              if Variable That Counts To Three    3                  shouldbreak  yes              break     print  Three Counter       str Variable That Counts To Three       Variable That Counts To Three  1     if shouldbreak     yes           break  print     This breaks out of two loops        This gives a lot of control over how exactly you want the program to break  allowing you to choose when you want to break and how many levels to go down

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Here s another approach that is short  The disadvantage is that you can only break the outer loop  but sometimes it s exactly what you want   for a in xrange 10       for b in xrange 20           if something a  b                 Break the inner loop                break     else            Continue if the inner loop wasn t broken          continue       Inner loop was broken  break the outer      break   This uses the for   else construct explained at  Why does python use   39 else  39  after for and while loops   Key insight   It only seems as if the outer loop always breaks  But if the inner loop doesn t break  the outer loop won t either    The continue statement is the magic here  It s in the for-else clause  By definition that happens if there s no inner break  In that situation continue neatly circumvents the outer break

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There is no way to do this from a language level  Some languages have   a goto others have a break that takes an argument  python does not       The best options are          Set a flag which is checked by the outer loop  or set the outer   loops condition    Put the loop in a function and use return to break out of all the loops at once    Reformulate your logic       Credit goes to Vivek Nagarajan  Programmer since 1987    Using Function   def doMywork data       for i in data         for e in i           return    Using flag  is break   False for i in data     if is break        break   outer loop break    for e in i        is break   True       break   inner loop break

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Similar like the one before  but more compact   Booleans are just numbers   breaker   False  our mighty loop exiter  while True      while True          ok   get input  Is this ok   y n            breaker    ok lower       y           break      if breaker    the interesting part          break      lt ---

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probably little trick like below will do if not prefer to refactorial into function  added 1 break level variable to control the while loop condition  break level   0   while break level  lt  3    if we have another level of nested loop here while break level  lt  2       snip  print out current state     while break level  lt  1          ok   get input  Is this ok   y n            if ok     y  or ok     Y   break level   2   break 2 level         if ok     n  or ok     N   break level   1   break 1 level

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This isn t the prettiest way to do it  but in my opinion  it s the best way  def loop        while True       snip  print out current state         while True              ok   get input  quot Is this ok   y n  quot               if ok     quot y quot  or ok     quot Y quot   return             if ok     quot n quot  or ok     quot N quot   break          do more processing with menus and stuff  I m pretty sure you could work out something using recursion here as well  but I don t know if that s a good option for you

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First  you may also consider making the process of getting and validating the input a function  within that function  you can just return the value if its correct  and keep spinning in the while loop if not   This essentially obviates the problem you solved  and can usually be applied in the more general case  breaking out of multiple loops    If you absolutely must keep this structure in your code  and really don t want to deal with bookkeeping booleans     You may also use goto in the following way  using an April Fools module from here     import the stuff from goto import goto  label  while True       snip  print out current state     while True          ok   get input  Is this ok   y n            if ok     y  or ok     Y   goto  breakall         if ok     n  or ok     N   break      do more processing with menus and stuff label  breakall   I know  I know   thou shalt not use goto  and all that  but it works well in strange cases like this

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You can define a variable  for example break statement    then change it to a different value when two-break condition occurs and use it in if statement to break from second loop also       while True      break statement 0     while True          ok   raw input  Is this ok   y n            if ok     n  or ok     N                break         if ok     y  or ok     Y                break statement 1             break     if break statement  1          break

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My first instinct would be to refactor the nested loop into a function and use return to break out

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keeplooping True while keeplooping       Do Stuff     while keeplooping             do some other stuff           if finisheddoingstuff                   keeplooping False  or something like that  You could set a variable in the inner loop  and check it in the outer loop immediately after the inner loop exits  breaking if appropriate  I kinda like the GOTO method  provided you don t mind using an April Fool s joke module - its not Pythonic  but it does make sense

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Here s an implementation that seems to work   break    False for i in range 10       if break           break     for j in range 10           if j    3              break    True             break         else              print i  j    The only draw back is that you have to define break  before the loops

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My first instinct would be to refactor the nested loop into a function and use return to break out

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There is a hidden trick in the Python while     else structure which can be used to simulate the double break without much code changes additions   In essence if the while condition is false  the else block is triggered  Neither exceptions  continue or break trigger the else block  For more information see answers to  Else clause on Python while statement   or Python doc on while  v2 7    while True       snip  print out current state     ok          while ok     y  and ok     n           ok   get input  Is this ok   y n            if ok     n  or ok     N               break      Breaks out of inner loop  skipping else      else          break          Breaks out of outer loop       do more processing with menus and stuff   The only downside is that you need to move the double breaking condition into the while condition  or add a flag variable   Variations of this exists also for the for loop  where the else block is triggered after loop completion

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Another way of reducing your iteration to a single-level loop would be via the use of generators as also specified in the python reference  for i  j in   i  j  for i in A for j in B       print i   j      if  some condition           break   You could scale it up to any number of levels for the loop  The downside is that you can no longer break only a single level  It s all or nothing   Another downside is that it doesn t work with a while loop  I originally wanted to post this answer on Python -  break  out of all loops but unfortunately that s closed as a duplicate of this one

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Another way of reducing your iteration to a single-level loop would be via the use of generators as also specified in the python reference  for i  j in   i  j  for i in A for j in B       print i   j      if  some condition           break   You could scale it up to any number of levels for the loop  The downside is that you can no longer break only a single level  It s all or nothing   Another downside is that it doesn t work with a while loop  I originally wanted to post this answer on Python -  break  out of all loops but unfortunately that s closed as a duplicate of this one

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this version uses a level counter to choose how far to break out  break levels   0 while True        snip  print out current state     while True          ok   get input  Is this ok   y n            if ok     y  or ok     Y               break levels   1          how far nested  excluding this break             break         if ok     n  or ok     N               break                     normal break     if break levels          break levels -  1         break                         pop another level if break levels      break levels -  1     break       and so on

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Hopefully this helps   x   True y   True while x    True      while y    True           ok   get input  Is this ok   y n              if ok     y  or ok     Y                x y   False False  breaks from both loops          if ok     n  or ok     N                 break  breaks from just one

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Introduce a new variable that you ll use as a  loop breaker   First assign something to it False 0  etc    and then  inside the outer loop  before you break from it  change the value to something else True 1       Once the loop exits make the  parent  loop check for that value  Let me demonstrate   breaker   False  our mighty loop exiter  while True      while True          if conditionMet               insert code here                breaker   True              break     if breaker    the interesting part          break      lt ---     If you have an infinite loop  this is the only way out  for other loops execution is really a lot faster  This also works if you have many nested loops  You can exit all  or just a few  Endless possibilities  Hope this helped

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probably little trick like below will do if not prefer to refactorial into function  added 1 break level variable to control the while loop condition  break level   0   while break level  lt  3    if we have another level of nested loop here while break level  lt  2       snip  print out current state     while break level  lt  1          ok   get input  Is this ok   y n            if ok     y  or ok     Y   break level   2   break 2 level         if ok     n  or ok     N   break level   1   break 1 level

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My reason for coming here is that i had an outer loop and an inner loop like so   for x in array    for y in dont use these values      if x value  y        array remove x     fixed  was array pop x  in my original answer       continue    do some other stuff with x   As you can see  it won t actually go to the next x  but will go to the next y instead   what i found to solve this simply was to run through the array twice instead   for x in array    for y in dont use these values      if x value  y        array remove x     fixed  was array pop x  in my original answer       continue  for x in array    do some other stuff with x   I know this was a specific case of OP s question  but I am posting it in the hope that it will help someone think about their problem differently while keeping things simple

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This isn t the prettiest way to do it  but in my opinion  it s the best way  def loop        while True       snip  print out current state         while True              ok   get input  quot Is this ok   y n  quot               if ok     quot y quot  or ok     quot Y quot   return             if ok     quot n quot  or ok     quot N quot   break          do more processing with menus and stuff  I m pretty sure you could work out something using recursion here as well  but I don t know if that s a good option for you

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this version uses a level counter to choose how far to break out  break levels   0 while True        snip  print out current state     while True          ok   get input  Is this ok   y n            if ok     y  or ok     Y               break levels   1          how far nested  excluding this break             break         if ok     n  or ok     N               break                     normal break     if break levels          break levels -  1         break                         pop another level if break levels      break levels -  1     break       and so on

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There is a hidden trick in the Python while     else structure which can be used to simulate the double break without much code changes additions   In essence if the while condition is false  the else block is triggered  Neither exceptions  continue or break trigger the else block  For more information see answers to  Else clause on Python while statement   or Python doc on while  v2 7    while True       snip  print out current state     ok          while ok     y  and ok     n           ok   get input  Is this ok   y n            if ok     n  or ok     N               break      Breaks out of inner loop  skipping else      else          break          Breaks out of outer loop       do more processing with menus and stuff   The only downside is that you need to move the double breaking condition into the while condition  or add a flag variable   Variations of this exists also for the for loop  where the else block is triggered after loop completion

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PEP 3136 proposes labeled break continue   Guido rejected it because  code so complicated to require this feature is very rare    The PEP does mention some workarounds  though  such as the exception technique   while Guido feels refactoring to use return will be simpler in most cases

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Since this question has become a standard question for breaking into a particular loop  I would like to give my answer with example using Exception    Although there exists no label named breaking of loop in multipally looped construct  we can make use of User-defined Exceptions to break into a particular loop of our choice  Consider the following example where let us print all numbers upto 4 digits in base-6 numbering system    class BreakLoop Exception       def   init   self  counter           Exception   init   self   Exception 1           self counter   counter  for counter1 in range 6       Make it 1000     try          thousand   counter1   1000         for counter2 in range 6      Make it 100             try                  hundred   counter2   100                 for counter3 in range 6     Make it 10                     try                          ten   counter3   10                         for counter4 in range 6                               try                                  unit   counter4                                 value   thousand   hundred   ten   unit                                 if unit    4                                       raise BreakLoop 4    Don t break from loop                                 if ten    30                                       raise BreakLoop 3    Break into loop 3                                 if hundred    500                                      raise BreakLoop 2    Break into loop 2                                 if thousand    2000                                      raise BreakLoop 1    Break into loop 1                                  print    04d   format value                               except BreakLoop as bl                                  if bl counter    4                                      raise bl                     except BreakLoop as bl                          if bl counter    3                              raise bl             except BreakLoop as bl                  if bl counter    2                      raise bl     except BreakLoop as bl          pass   When we print the output  we will never get any value whose unit place is with 4  In that case  we don t break from any loop as BreakLoop 4  is raised and caught in same loop  Similarly  whenever ten place is having 3  we break into third loop using BreakLoop 3   Whenever hundred place is having 5  we break into second loop using BreakLoop 2  and whenver the thousand place is having 2  we break into first loop using BreakLoop 1    In short  raise your Exception  in-built or user defined  in the inner loops  and catch it in the loop from where you want to resume your control to  If you want to break from all loops  catch the Exception outside all the loops   I have not shown this case in example

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keeplooping True while keeplooping       Do Stuff     while keeplooping             do some other stuff           if finisheddoingstuff                   keeplooping False  or something like that  You could set a variable in the inner loop  and check it in the outer loop immediately after the inner loop exits  breaking if appropriate  I kinda like the GOTO method  provided you don t mind using an April Fool s joke module - its not Pythonic  but it does make sense

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To break out of multiple nested loops  without refactoring into a function  make use of a  simulated goto statement  with the built-in StopIteration exception   try      for outer in range 100           for inner in range 100               if break early                    raise StopIteration  except StopIteration  pass   See this discussion on the use of goto statements for breaking out of nested loops

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The way I solve this is by defining a variable that is referenced to determine if you break to the next level or not  In this example  this variable is called  shouldbreak    Variable That Counts To Three 1 while 1  1      shouldbreak  no      Variable That Counts To Five 0     while 2  2          Variable That Counts To Five  1         print Variable That Counts To Five          if Variable That Counts To Five    5              if Variable That Counts To Three    3                  shouldbreak  yes              break     print  Three Counter       str Variable That Counts To Three       Variable That Counts To Three  1     if shouldbreak     yes           break  print     This breaks out of two loops        This gives a lot of control over how exactly you want the program to break  allowing you to choose when you want to break and how many levels to go down

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First  you may also consider making the process of getting and validating the input a function  within that function  you can just return the value if its correct  and keep spinning in the while loop if not   This essentially obviates the problem you solved  and can usually be applied in the more general case  breaking out of multiple loops    If you absolutely must keep this structure in your code  and really don t want to deal with bookkeeping booleans     You may also use goto in the following way  using an April Fools module from here     import the stuff from goto import goto  label  while True       snip  print out current state     while True          ok   get input  Is this ok   y n            if ok     y  or ok     Y   goto  breakall         if ok     n  or ok     N   break      do more processing with menus and stuff label  breakall   I know  I know   thou shalt not use goto  and all that  but it works well in strange cases like this

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I tend to agree that refactoring into a function is usually the best approach for this sort of situation  but for when you really need to break out of nested loops  here s an interesting variant of the exception-raising approach that  S Lott described   It uses Python s with statement to make the exception raising look a bit nicer   Define a new context manager  you only have to do this once  with   from contextlib import contextmanager  contextmanager def nested break        class NestedBreakException Exception           pass     try          yield NestedBreakException     except NestedBreakException          pass   Now you can use this context manager as follows   with nested break   as mylabel      while True          print  current state          while True              ok   raw input  Is this ok   y n                if ok     y  or ok     Y   raise mylabel             if ok     n  or ok     N   break         print  more processing    Advantages   1  it s slightly cleaner  no explicit try-except block   and  2  you get a custom-built Exception subclass for each use of nested break   no need to declare your own Exception subclass each time

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Introduce a new variable that you ll use as a  loop breaker   First assign something to it False 0  etc    and then  inside the outer loop  before you break from it  change the value to something else True 1       Once the loop exits make the  parent  loop check for that value  Let me demonstrate   breaker   False  our mighty loop exiter  while True      while True          if conditionMet               insert code here                breaker   True              break     if breaker    the interesting part          break      lt ---     If you have an infinite loop  this is the only way out  for other loops execution is really a lot faster  This also works if you have many nested loops  You can exit all  or just a few  Endless possibilities  Hope this helped

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I tend to agree that refactoring into a function is usually the best approach for this sort of situation  but for when you really need to break out of nested loops  here s an interesting variant of the exception-raising approach that  S Lott described   It uses Python s with statement to make the exception raising look a bit nicer   Define a new context manager  you only have to do this once  with   from contextlib import contextmanager  contextmanager def nested break        class NestedBreakException Exception           pass     try          yield NestedBreakException     except NestedBreakException          pass   Now you can use this context manager as follows   with nested break   as mylabel      while True          print  current state          while True              ok   raw input  Is this ok   y n                if ok     y  or ok     Y   raise mylabel             if ok     n  or ok     N   break         print  more processing    Advantages   1  it s slightly cleaner  no explicit try-except block   and  2  you get a custom-built Exception subclass for each use of nested break   no need to declare your own Exception subclass each time

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PEP 3136 proposes labeled break continue   Guido rejected it because  code so complicated to require this feature is very rare    The PEP does mention some workarounds  though  such as the exception technique   while Guido feels refactoring to use return will be simpler in most cases

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Here s another approach that is short  The disadvantage is that you can only break the outer loop  but sometimes it s exactly what you want   for a in xrange 10       for b in xrange 20           if something a  b                 Break the inner loop                break     else            Continue if the inner loop wasn t broken          continue       Inner loop was broken  break the outer      break   This uses the for   else construct explained at  Why does python use   39 else  39  after for and while loops   Key insight   It only seems as if the outer loop always breaks  But if the inner loop doesn t break  the outer loop won t either    The continue statement is the magic here  It s in the for-else clause  By definition that happens if there s no inner break  In that situation continue neatly circumvents the outer break

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This isn t the prettiest way to do it  but in my opinion  it s the best way  def loop        while True       snip  print out current state         while True              ok   get input  quot Is this ok   y n  quot               if ok     quot y quot  or ok     quot Y quot   return             if ok     quot n quot  or ok     quot N quot   break          do more processing with menus and stuff  I m pretty sure you could work out something using recursion here as well  but I don t know if that s a good option for you

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First  ordinary logic is helpful     If  for some reason  the terminating conditions can t be worked out  exceptions are a fall-back plan     class GetOutOfLoop  Exception        pass  try      done  False     while not done          isok  False         while not  done or isok               ok   get input  Is this ok   y n                if ok in   y    Y   or ok in   n    N                      done  True   probably better                 raise GetOutOfLoop           other stuff except GetOutOfLoop      pass   For this specific example  an exception may not be necessary     On other other hand  we often have  Y    N  and  Q  options in character-mode applications   For the  Q  option  we want an immediate exit   That s more exceptional

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An easy way to turn multiple loops into a single  breakable loop is to use numpy ndindex  for i in range n     for j in range n       val   x i  j      break   still inside the outer loop   for i  j in np ndindex n  n     val   x i  j    break   you left the only loop there was    You do have to index into your objects  as opposed to being able to iterate through the values explicitly  but at least in simple cases it seems to be approximately 2-20 times simpler than most of the answers suggested

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My reason for coming here is that i had an outer loop and an inner loop like so   for x in array    for y in dont use these values      if x value  y        array remove x     fixed  was array pop x  in my original answer       continue    do some other stuff with x   As you can see  it won t actually go to the next x  but will go to the next y instead   what i found to solve this simply was to run through the array twice instead   for x in array    for y in dont use these values      if x value  y        array remove x     fixed  was array pop x  in my original answer       continue  for x in array    do some other stuff with x   I know this was a specific case of OP s question  but I am posting it in the hope that it will help someone think about their problem differently while keeping things simple

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this version breaks up to a certain label  break label   None while True        snip  print out current state     while True          ok   get input  Is this ok   y n            if ok     y  or ok     Y               break label    outer      specify label to break to             break         if ok     n  or ok     N               break     if break label          if break label     inner               break                     propagate up         break label   None            we have arrived  if break label      if break label     outer           break                         propagate up     break label   None                we have arrived    do more processing with menus and stuff

User · Answer

First  ordinary logic is helpful     If  for some reason  the terminating conditions can t be worked out  exceptions are a fall-back plan     class GetOutOfLoop  Exception        pass  try      done  False     while not done          isok  False         while not  done or isok               ok   get input  Is this ok   y n                if ok in   y    Y   or ok in   n    N                      done  True   probably better                 raise GetOutOfLoop           other stuff except GetOutOfLoop      pass   For this specific example  an exception may not be necessary     On other other hand  we often have  Y    N  and  Q  options in character-mode applications   For the  Q  option  we want an immediate exit   That s more exceptional

User · Answer

In this case  as pointed out by others as well  functional decomposition is the way to go  Code in Python 3   def user confirms        while True          answer   input  Is this OK   y n     strip   lower           if answer in  yn               return answer     y   def main        while True            do stuff         if user confirms                break

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There is no way to do this from a language level  Some languages have   a goto others have a break that takes an argument  python does not       The best options are          Set a flag which is checked by the outer loop  or set the outer   loops condition    Put the loop in a function and use return to break out of all the loops at once    Reformulate your logic       Credit goes to Vivek Nagarajan  Programmer since 1987    Using Function   def doMywork data       for i in data         for e in i           return    Using flag  is break   False for i in data     if is break        break   outer loop break    for e in i        is break   True       break   inner loop break

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PEP 3136 proposes labeled break continue   Guido rejected it because  code so complicated to require this feature is very rare    The PEP does mention some workarounds  though  such as the exception technique   while Guido feels refactoring to use return will be simpler in most cases

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And why not to keep looping if two conditions are true  I think this is a more pythonic way   dejaVu   True  while dejaVu      while True          ok   raw input  Is this ok   y n            if ok     y  or ok     Y  or ok     n  or ok     N               dejaVu   False             break   Isn t it   All the best

User · Answer

Here s an implementation that seems to work   break    False for i in range 10       if break           break     for j in range 10           if j    3              break    True             break         else              print i  j    The only draw back is that you have to define break  before the loops

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Solutions in 2 Ways  With an example  Are these two matrices equal same   matrix1 and matrix2 are same size  n  2 dimentional matrices   First Solution  without a function   same matrices   True inner loop broken once   False n   len matrix1   for i in range n       for j in range n            if matrix1 i  j     matrix2 i  j               same matrices   False             inner loop broken once   True             break      if inner loop broken once          break     Second Solution  with a function  This is the final solution for my case   def are two matrices the same  matrix1  matrix2       n   len matrix1      for i in range n           for j in range n               if matrix1 i  j     matrix2 i  j                   return False     return True   Have a nice day

User · Answer

Try using an infinite generator   from itertools import repeat inputs    get input  Is this ok   y n    for   in repeat None   response    i lower     y  for i in inputs if i lower   in   y    n     while True       snip  print out current state     if next response           break      do more processing with menus and stuff

User · Answer

Factor your loop logic into an iterator that yields the loop variables and returns when done -- here is a simple one that lays out images in rows columns until we re out of images or out of places to put them   def it rows  cols  images       i   0     for r in xrange rows           for c in xrange cols               if i  gt   len images                   return             yield r  c  images i              i    1   for r  c  image in it rows 4  cols 4  images   a jpg    b jpg    c jpg             do something with r  c  image       This has the advantage of splitting up the complicated loop logic and the processing

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First  ordinary logic is helpful     If  for some reason  the terminating conditions can t be worked out  exceptions are a fall-back plan     class GetOutOfLoop  Exception        pass  try      done  False     while not done          isok  False         while not  done or isok               ok   get input  Is this ok   y n                if ok in   y    Y   or ok in   n    N                      done  True   probably better                 raise GetOutOfLoop           other stuff except GetOutOfLoop      pass   For this specific example  an exception may not be necessary     On other other hand  we often have  Y    N  and  Q  options in character-mode applications   For the  Q  option  we want an immediate exit   That s more exceptional

User · Answer

PEP 3136 proposes labeled break continue   Guido rejected it because  code so complicated to require this feature is very rare    The PEP does mention some workarounds  though  such as the exception technique   while Guido feels refactoring to use return will be simpler in most cases

User · Answer

I d like to remind you that functions in Python can be created right in the middle of the code and can access the surrounding variables transparently for reading and with nonlocal or global declaration for writing   So you can use a function as a  breakable control structure   defining a place you want to return to   def is prime number        foo   bar   number      def return here            nonlocal foo  bar         init bar   bar         while foo  gt  0              bar   init bar             while bar  gt   foo                  if foo bar    number                      return                 bar -  1             foo -  1      return here        if foo    1          print number   is prime       else          print number       bar       foo       gt  gt  gt  is prime 67  67 is prime  gt  gt  gt  is prime 117  117   13   9  gt  gt  gt  is prime 16  16   4   4

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Similar like the one before  but more compact   Booleans are just numbers   breaker   False  our mighty loop exiter  while True      while True          ok   get input  Is this ok   y n            breaker    ok lower       y           break      if breaker    the interesting part          break      lt ---

User · Answer

First  you may also consider making the process of getting and validating the input a function  within that function  you can just return the value if its correct  and keep spinning in the while loop if not   This essentially obviates the problem you solved  and can usually be applied in the more general case  breaking out of multiple loops    If you absolutely must keep this structure in your code  and really don t want to deal with bookkeeping booleans     You may also use goto in the following way  using an April Fools module from here     import the stuff from goto import goto  label  while True       snip  print out current state     while True          ok   get input  Is this ok   y n            if ok     y  or ok     Y   goto  breakall         if ok     n  or ok     N   break      do more processing with menus and stuff label  breakall   I know  I know   thou shalt not use goto  and all that  but it works well in strange cases like this

[python] How to break out of multiple loops?

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