Python Continuing to next iteration in outer loop

Question

I wanted to know if there are any built-in ways to continue to next iteration in outer loop in python   For example   consider the code   for ii in range 200       for jj in range 200  400              block0            if something              continue        block1      I want this continue statement to exit the jj loop and goto next item in the ii loop   I can implement this logic in some other way  by setting a flag variable   but is there an easy way to do this  or is this like asking for too much

User · Answer

We want to find something and then stop the inner iteration  I use a flag system   for l in f      flag   True     for e in r          if flag  False continue         if somecondition              do something               flag False

User · Answer

for ii in range 200       for jj in range 200  400              block0            if something              break     else             block1      Break will break the inner loop  and block1 won t be executed  it will run only if the inner loop is exited normally

User · Answer

I just did something like this  My solution for this was to replace the interior for loop with a list comprehension    for ii in range 200       done   any  op ii  jj  for jj in range 200  400           block0        if done          continue        block1      where op is some boolean operator acting on a combination of ii and jj  In my case  if any of the operations returned true  I was done   This is really not that different from breaking the code out into a function  but I thought that using the  any  operator to do a logical OR on a list of booleans and doing the logic all in one line was interesting  It also avoids the function call

User · Answer

I think one of the easiest ways to achieve this is to replace  continue  with  break  statement i e   for ii in range 200    for jj in range 200  400          block0        if something          break     block1             For example  here is the easy code to see how exactly it goes on   for i in range 10       print  doing outer loop       print  i   i      for p in range 10           print  doing inner loop           print  p   p          if p  3              print  breaking from inner loop               break     print  doing some code in outer loop

User · Answer

Another way to deal with this kind of problem is to use Exception     for ii in range 200       try          for jj in range 200  400                  block0                if something                  raise Exception       except Exception          continue        block1      For example   for n in range 1 4       for m in range 1 4           print n  -  m   result       1-1     1-2     1-3     2-1     2-2     2-3     3-1     3-2     3-3   Assuming we want to jump to the outer n loop from m loop if m  3   for n in range 1 4       try          for m in range 1 4               if m    3                  raise Exception                           print n  -  m     except Exception          continue   result       1-1     1-2     2-1     2-2     3-1     3-2   Reference link http   www programming-idioms org idiom 42 continue-outer-loop 1264 python

User · Answer

I think you could do something like this   for ii in range 200       restart   False     for jj in range 200  400              block0            if something              restart   True             break     if restart          continue        block1

User · Answer

In other languages you can label the loop and break from the labelled loop   Python Enhancement Proposal  PEP  3136 suggested adding these to Python but Guido rejected it      However  I m rejecting it on the basis that code so complicated to   require this feature is very rare  In most cases there are existing   work-arounds that produce clean code  for example using  return     While I m sure there are some  rare  real cases where clarity of the   code would suffer from a refactoring that makes it possible to use   return  this is offset by two issues          The complexity added to the language  permanently  This affects not   only all Python implementations  but also every source analysis tool    plus of course all documentation for the language    My expectation that the feature will be abused more than it will be   used right  leading to a net decrease in code clarity  measured across   all Python code written henceforth   Lazy programmers are everywhere    and before you know it you have an incredible mess on your hands of   unintelligible code       So if that s what you were hoping for you re out of luck  but look at one of the other answers as there are good options there

User · Answer

for i in          for j in              for k in                  if something                    continue loop i   In a general case  when you have multiple levels of looping and break does not work for you  because you want to continue one of the upper loops  not the one right above the current one   you can do one of the following  Refactor the loops you want to escape from into a function  def inner        for j in              for k in                  if something                  return   for i in          inner     The disadvantage is that you may need to pass to that new function some variables  which were previously in scope  You can either just pass them as parameters  make them instance variables on an object  create a new object just for this function  if it makes sense   or global variables  singletons  whatever  ehm  ehm    Or you can define inner as a nested function and let it just capture what it needs  may be slower    for i in          def inner            for j in                  for k in                      if something                      return     inner     Use exceptions  Philosophically  this is what exceptions are for  breaking the program flow through the structured programming building blocks  if  for  while  when necessary   The advantage is that you don t have to break the single piece of code into multiple parts  This is good if it is some kind of computation that you are designing while writing it in Python  Introducing abstractions at this early point may slow you down   Bad thing with this approach is that interpreter compiler authors usually assume that exceptions are exceptional and optimize for them accordingly   class ContinueI Exception       pass   continue i   ContinueI    for i in          try          for j in                  for k in                      if something                      raise continue i     except ContinueI          continue   Create a special exception class for this  so that you don t risk accidentally silencing some other exception   Something else entirely  I am sure there are still other solutions

[python] Python: Continuing to next iteration in outer loop

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