Is there a label goto in Python

Question

Is there a goto or any equivalent in Python to be able to jump to a specific line of code

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Python 2  amp  3  pip3 install goto-statement      Tested on Python 2 6 through 3 6 and PyPy    Link  goto-statement    foo py  from goto import with goto   with goto def bar         label  bar begin               goto  bar begin

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In lieu of a python goto equivalent I use the break statement in the following fashion for quick tests of my code  This assumes you have structured code base  The test variable is initialized at the start of your function and I just move the  If test  break  block to the end of the nested if-then block or loop I want to test  modifying the return variable at the end of the code to reflect the block or loop variable I m testing   def x    test   True   If y         some code      If test              break   return something

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It is technically feasible to add a  goto  like statement to python with some work  We will use the  dis  and  new  modules  both very useful for scanning and modifying python byte code   The main idea behind the implementation is to first mark a block of code as using  goto  and  label  statements  A special   goto  decorator will be used for the purpose of marking  goto  functions  Afterwards we scan that code for these two statements and apply the necessary modifications to the underlying byte code  This all happens at source code compile time   import dis  new  def goto fn               A function decorator to add the goto command for a function           Specify labels like so          label  foo          Goto labels like so          goto  foo          Note  you can write a goto statement before the correspnding label statement             labels          gotos          globalName   None     index   0     end   len fn func code co code      i   0        scan through the byte codes to find the labels and gotos     while i  lt  end          op   ord fn func code co code i           i    1         name   dis opname op           if op  gt  dis HAVE ARGUMENT              b1   ord fn func code co code i               b2   ord fn func code co code i 1               num   b2   256   b1              if name     LOAD GLOBAL                   globalName   fn func code co names num                  index   i - 1                 i    2                 continue              if name     LOAD ATTR                   if globalName     label                       labels fn func code co names num     index                 elif globalName     goto                       gotos fn func code co names num     index              name   None             i    2        no-op the labels     ilist   list fn func code co code      for label index in labels items            ilist index index 7     chr dis opmap  NOP     7        change gotos to jumps     for label index in gotos items            if label not in labels              raise Exception  Missing label   s  label           target   labels label    7     skip NOPs         ilist index    chr dis opmap  JUMP ABSOLUTE            ilist index   1    chr target  amp  255          ilist index   2    chr target  gt  gt  8         create new function from existing function     c   fn func code     newcode   new code c co argcount                         c co nlocals                         c co stacksize                         c co flags                            join ilist                          c co consts                         c co names                         c co varnames                         c co filename                         c co name                         c co firstlineno                         c co lnotab      newfn   new function newcode fn func globals      return newfn   if   name         main           goto     def test1            print  Hello            goto  the end         print  world           label  the end         print  the end       test1     Hope this answers the question

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I have my own way of doing gotos  I use separate python scripts   If I want to loop   file1 py   print  test test   execfile  file2 py   a   a   1   file2 py  print a  if a    10     execfile  file3 py   else     execfile  file1 py     file3 py  print a     equals 10      NOTE  This technique only works on Python 2 x versions

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To answer the  ascobol s question using  bobince s suggestion from the comments   for i in range 5000       for j in range 3000           if should terminate the loop             break     else           continue   no break encountered     break   The indent for the else block is correct  The code uses obscure else after a loop Python syntax  See Why does python use  else  after for and while loops

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Python 2  amp  3  pip3 install goto-statement      Tested on Python 2 6 through 3 6 and PyPy    Link  goto-statement    foo py  from goto import with goto   with goto def bar         label  bar begin               goto  bar begin

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Python offers you the ability to do some of the things you could do with a goto using first class functions   For example   void somefunc int a        if  a    1          goto label1      if  a    2          goto label2       label1                  label2                  Could be done in python like this   def func1             def func2             funcmap    1   func1  2   func2   def somefunc a       funcmap a      Ugly   But it works    Granted  that isn t the best way to substitute for goto   But without knowing exactly what you re trying to do with the goto  it s hard to give specific advice    ascobol   Your best bet is to either enclose it in a function or use an exception   For the function   def loopfunc        while 1          while 1              if condition                  return   For the exception   try      while 1          while 1              raise BreakoutException  Not a real exception  invent your own except BreakoutException      pass   Using exceptions to do stuff like this may feel a bit awkward if you come from another programming language   But I would argue that if you dislike using exceptions  Python isn t the language for you    -

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I was looking for some thing similar to  for a in xrange 1 10   A LOOP     for b in xrange 1 5           for c in xrange 1 5               for d in xrange 1 5                     do some stuff                 if condition e                        goto B LOOP    So my approach was to use a boolean to help breaking out from the nested for loops   for a in xrange 1 10       get out   False     for b in xrange 1 5           if get out   break         for c in xrange 1 5               if get out   break             for d in xrange 1 5                     do some stuff                 if condition e                        get out   True                     break

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Though there isn t any code equivalent to goto label in Python  you could still get such functionality of goto label using loops     Lets take a code sample shown below where goto label can be used in a arbitrary language other than python   String str1    BACK   label1      print  Hello  this program contains goto code n       print  Now type BACK if you want the program to go back to the above line of code  Or press the ENTER key if you want the program to continue with further lines of code       str1   input    if str1     BACK                GoTo label1       print  Program will continue nBla bla bla    nBla bla bla    nBla bla bla        Now the same functionality of the above code sample can be achieved in python by using a while loop as shown below     str1    BACK   while str1     BACK           print  Hello  this is a python program containing python equivalent code for goto code n           print  Now type BACK if you want the program to go back to the above line of code  Or press the ENTER key if you want the program to continue with further lines of code           str1   input   print  Program will continue nBla bla bla    nBla bla bla    nBla bla bla

User · Answer

I have my own way of doing gotos  I use separate python scripts   If I want to loop   file1 py   print  test test   execfile  file2 py   a   a   1   file2 py  print a  if a    10     execfile  file3 py   else     execfile  file1 py     file3 py  print a     equals 10      NOTE  This technique only works on Python 2 x versions

User · Answer

no there is an alternative way to implement goto statement  class id       def data1 self           name            age               n 1         while n gt 0              print  1  for enter data               print  2  update list               print  3  show data               print  choose what you want to do                 ch int input  enter your choice                if ch  1                      n int input  how many elemet you want to enter                     for i in range n                       name append input  NAME                         age append int input  age                   elif ch  2                  name append input  NAME                     age append int input  age                  elif ch  3                  try                      if name  None                          print  empty list                       else                          print  name  t age                           for i in range n                               print name i     t   age i                           break                 except                      print  list is empty               print  do want to continue y or n               ch1 input               if ch1   y                   n n 1             else                  print  name  t age                   for i in range n                       print name i     t   age i                   n -1 p1 id   p1 data1

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Labels for break and continue were proposed in PEP 3136 back in 2007  but it was rejected   The Motivation section of the proposal illustrates several common  if inelegant  methods for imitating labeled break in Python

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No  Python does not support labels and goto  if that is what you re after  It s a  highly  structured programming language

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you can use User-defined Exceptions to emulate goto  example   class goto1 Exception       pass    class goto2 Exception       pass    class goto3 Exception       pass      def loop        print  start      num   input       try          if num lt  0              raise goto1         elif num lt  2              raise goto2         elif num lt  4              raise goto3         elif num lt  6              raise goto1         else              print  end              return 0     except goto1 as e          print  goto1          loop       except goto2 as e          print  goto2          loop       except goto3 as e          print  goto3          loop

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A working version has been made  http   entrian com goto    Note  It was offered as an April Fool s joke   working though     Example 1  Breaking out from a deeply nested loop  from goto import goto  label  for i in range 1  10       for j in range 1  20           for k in range 1  30               print i  j  k             if k    3                  goto  end label  end print  Finished n    Needless to say  Yes its funny  but DONT use it

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I recently wrote a function decorator that enables goto in Python  just like that   from goto import with goto   with goto def range start  stop       i   start     result           label  begin     if i    stop          goto  end      result append i      i    1     goto  begin      label  end     return result   I m not sure why one would like to do something like that though  That said  I m not too serious about it  But I d like to point out that this kind of meta programming is actual possible in Python  at least in CPython and PyPy  and not only by misusing the debugger API as that other guy did  You have to mess with the bytecode though

User · Answer

No  Python does not support labels and goto  if that is what you re after  It s a  highly  structured programming language

User · Answer

For a forward Goto  you could just add   while True    if some condition      break        extra code   break   force code to exit  Needed at end of while loop      continues here   This only helps for simple scenarios though  i e  nesting these would get you into a mess

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For a forward Goto  you could just add   while True    if some condition      break        extra code   break   force code to exit  Needed at end of while loop      continues here   This only helps for simple scenarios though  i e  nesting these would get you into a mess

User · Answer

I was looking for some thing similar to  for a in xrange 1 10   A LOOP     for b in xrange 1 5           for c in xrange 1 5               for d in xrange 1 5                     do some stuff                 if condition e                        goto B LOOP    So my approach was to use a boolean to help breaking out from the nested for loops   for a in xrange 1 10       get out   False     for b in xrange 1 5           if get out   break         for c in xrange 1 5               if get out   break             for d in xrange 1 5                     do some stuff                 if condition e                        get out   True                     break

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I wanted the same answer and I didnt want to use goto  So I used the following example  from learnpythonthehardway   def sample        print  This room is full of gold how much do you want       choice   raw input   gt         how much   int choice      if  0  in choice or  1  in choice          check how much      else          print  Enter a number with 0 or 1          sample    def check n       if n  lt  150          print  You are not greedy  you win          exit 0      else          print  You are nuts           exit 0

User · Answer

No  Python does not support labels and goto  if that is what you re after  It s a  highly  structured programming language

User · Answer

I wanted the same answer and I didnt want to use goto  So I used the following example  from learnpythonthehardway   def sample        print  This room is full of gold how much do you want       choice   raw input   gt         how much   int choice      if  0  in choice or  1  in choice          check how much      else          print  Enter a number with 0 or 1          sample    def check n       if n  lt  150          print  You are not greedy  you win          exit 0      else          print  You are nuts           exit 0

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I think while loop is alternate for the  quot goto Statement quot   Because after 3 6 goto loop is not working anymore  I also write an example of the while loop  str1    quot stop quot  while str1     quot back quot       var1   int input  quot  Enter Ist Number   quot        var2   int input  quot  Enter 2nd Number   quot        var3   print  quot  quot  quot   What is your next operation                       For Addition   Press And Enter    A                        For Muliplt    Press And Enter    M                        For Division   Press And Enter    D                        For Subtaction Press And Enter    S   quot  quot  quot        var4   str input  quot For operation press any number    quot        if var1    45  and  var2    3           print  quot 555 quot       elif var1    56  and  var2    9           print  quot 77 quot       elif var1    56  and  var2    6           print  quot 4 quot       else          if var4     quot A quot  or  quot a quot                print var1   var2          if var4     quot M quot  or  quot m quot                print var1   var2          if var4     quot D quot  or  quot d quot                print var1   var2          if var4     quot S quot  or  quot s quot                print var1 - var2       print  quot if you want to continue then type   stop  quot        str1   input   print  quot Strt again quot

User · Answer

you can use User-defined Exceptions to emulate goto  example   class goto1 Exception       pass    class goto2 Exception       pass    class goto3 Exception       pass      def loop        print  start      num   input       try          if num lt  0              raise goto1         elif num lt  2              raise goto2         elif num lt  4              raise goto3         elif num lt  6              raise goto1         else              print  end              return 0     except goto1 as e          print  goto1          loop       except goto2 as e          print  goto2          loop       except goto3 as e          print  goto3          loop

User · Answer

I found this in the official python Design and History FAQ      Why is there no goto       You can use exceptions to provide a    structured goto    that even works   across function calls  Many feel that exceptions can conveniently   emulate all reasonable uses of the    go    or    goto    constructs of C    Fortran  and other languages  For example    class label Exception   pass    declare a label  try              if condition  raise label      goto label         except label     where to goto     pass           This doesn   t allow you to jump into the middle of a loop  but that   s   usually considered an abuse of goto anyway  Use sparingly    It s very nice that this is even mentioned in the official FAQ  and that a nice solution sample is provided  I really like python because its community is treating even goto like this

User · Answer

I recently wrote a function decorator that enables goto in Python  just like that   from goto import with goto   with goto def range start  stop       i   start     result           label  begin     if i    stop          goto  end      result append i      i    1     goto  begin      label  end     return result   I m not sure why one would like to do something like that though  That said  I m not too serious about it  But I d like to point out that this kind of meta programming is actual possible in Python  at least in CPython and PyPy  and not only by misusing the debugger API as that other guy did  You have to mess with the bytecode though

User · Answer

It is technically feasible to add a  goto  like statement to python with some work  We will use the  dis  and  new  modules  both very useful for scanning and modifying python byte code   The main idea behind the implementation is to first mark a block of code as using  goto  and  label  statements  A special   goto  decorator will be used for the purpose of marking  goto  functions  Afterwards we scan that code for these two statements and apply the necessary modifications to the underlying byte code  This all happens at source code compile time   import dis  new  def goto fn               A function decorator to add the goto command for a function           Specify labels like so          label  foo          Goto labels like so          goto  foo          Note  you can write a goto statement before the correspnding label statement             labels          gotos          globalName   None     index   0     end   len fn func code co code      i   0        scan through the byte codes to find the labels and gotos     while i  lt  end          op   ord fn func code co code i           i    1         name   dis opname op           if op  gt  dis HAVE ARGUMENT              b1   ord fn func code co code i               b2   ord fn func code co code i 1               num   b2   256   b1              if name     LOAD GLOBAL                   globalName   fn func code co names num                  index   i - 1                 i    2                 continue              if name     LOAD ATTR                   if globalName     label                       labels fn func code co names num     index                 elif globalName     goto                       gotos fn func code co names num     index              name   None             i    2        no-op the labels     ilist   list fn func code co code      for label index in labels items            ilist index index 7     chr dis opmap  NOP     7        change gotos to jumps     for label index in gotos items            if label not in labels              raise Exception  Missing label   s  label           target   labels label    7     skip NOPs         ilist index    chr dis opmap  JUMP ABSOLUTE            ilist index   1    chr target  amp  255          ilist index   2    chr target  gt  gt  8         create new function from existing function     c   fn func code     newcode   new code c co argcount                         c co nlocals                         c co stacksize                         c co flags                            join ilist                          c co consts                         c co names                         c co varnames                         c co filename                         c co name                         c co firstlineno                         c co lnotab      newfn   new function newcode fn func globals      return newfn   if   name         main           goto     def test1            print  Hello            goto  the end         print  world           label  the end         print  the end       test1     Hope this answers the question

User · Answer

To answer the  ascobol s question using  bobince s suggestion from the comments   for i in range 5000       for j in range 3000           if should terminate the loop             break     else           continue   no break encountered     break   The indent for the else block is correct  The code uses obscure else after a loop Python syntax  See Why does python use  else  after for and while loops

User · Answer

Python offers you the ability to do some of the things you could do with a goto using first class functions   For example   void somefunc int a        if  a    1          goto label1      if  a    2          goto label2       label1                  label2                  Could be done in python like this   def func1             def func2             funcmap    1   func1  2   func2   def somefunc a       funcmap a      Ugly   But it works    Granted  that isn t the best way to substitute for goto   But without knowing exactly what you re trying to do with the goto  it s hard to give specific advice    ascobol   Your best bet is to either enclose it in a function or use an exception   For the function   def loopfunc        while 1          while 1              if condition                  return   For the exception   try      while 1          while 1              raise BreakoutException  Not a real exception  invent your own except BreakoutException      pass   Using exceptions to do stuff like this may feel a bit awkward if you come from another programming language   But I would argue that if you dislike using exceptions  Python isn t the language for you    -

User · Answer

Labels for break and continue were proposed in PEP 3136 back in 2007  but it was rejected   The Motivation section of the proposal illustrates several common  if inelegant  methods for imitating labeled break in Python

User · Answer

There is now  goto  I think this might be useful for what you are looking for

User · Answer

In lieu of a python goto equivalent I use the break statement in the following fashion for quick tests of my code  This assumes you have structured code base  The test variable is initialized at the start of your function and I just move the  If test  break  block to the end of the nested if-then block or loop I want to test  modifying the return variable at the end of the code to reflect the block or loop variable I m testing   def x    test   True   If y         some code      If test              break   return something

User · Answer

no there is an alternative way to implement goto statement  class id       def data1 self           name            age               n 1         while n gt 0              print  1  for enter data               print  2  update list               print  3  show data               print  choose what you want to do                 ch int input  enter your choice                if ch  1                      n int input  how many elemet you want to enter                     for i in range n                       name append input  NAME                         age append int input  age                   elif ch  2                  name append input  NAME                     age append int input  age                  elif ch  3                  try                      if name  None                          print  empty list                       else                          print  name  t age                           for i in range n                               print name i     t   age i                           break                 except                      print  list is empty               print  do want to continue y or n               ch1 input               if ch1   y                   n n 1             else                  print  name  t age                   for i in range n                       print name i     t   age i                   n -1 p1 id   p1 data1

User · Answer

No  Python does not support labels and goto  if that is what you re after  It s a  highly  structured programming language

User · Answer

To answer the  ascobol s question using  bobince s suggestion from the comments   for i in range 5000       for j in range 3000           if should terminate the loop             break     else           continue   no break encountered     break   The indent for the else block is correct  The code uses obscure else after a loop Python syntax  See Why does python use  else  after for and while loops

User · Answer

Python offers you the ability to do some of the things you could do with a goto using first class functions   For example   void somefunc int a        if  a    1          goto label1      if  a    2          goto label2       label1                  label2                  Could be done in python like this   def func1             def func2             funcmap    1   func1  2   func2   def somefunc a       funcmap a      Ugly   But it works    Granted  that isn t the best way to substitute for goto   But without knowing exactly what you re trying to do with the goto  it s hard to give specific advice    ascobol   Your best bet is to either enclose it in a function or use an exception   For the function   def loopfunc        while 1          while 1              if condition                  return   For the exception   try      while 1          while 1              raise BreakoutException  Not a real exception  invent your own except BreakoutException      pass   Using exceptions to do stuff like this may feel a bit awkward if you come from another programming language   But I would argue that if you dislike using exceptions  Python isn t the language for you    -

User · Answer

To answer the  ascobol s question using  bobince s suggestion from the comments   for i in range 5000       for j in range 3000           if should terminate the loop             break     else           continue   no break encountered     break   The indent for the else block is correct  The code uses obscure else after a loop Python syntax  See Why does python use  else  after for and while loops

User · Answer

There is now  goto  I think this might be useful for what you are looking for

User · Answer

Python offers you the ability to do some of the things you could do with a goto using first class functions   For example   void somefunc int a        if  a    1          goto label1      if  a    2          goto label2       label1                  label2                  Could be done in python like this   def func1             def func2             funcmap    1   func1  2   func2   def somefunc a       funcmap a      Ugly   But it works    Granted  that isn t the best way to substitute for goto   But without knowing exactly what you re trying to do with the goto  it s hard to give specific advice    ascobol   Your best bet is to either enclose it in a function or use an exception   For the function   def loopfunc        while 1          while 1              if condition                  return   For the exception   try      while 1          while 1              raise BreakoutException  Not a real exception  invent your own except BreakoutException      pass   Using exceptions to do stuff like this may feel a bit awkward if you come from another programming language   But I would argue that if you dislike using exceptions  Python isn t the language for you    -

User · Answer

I found this in the official python Design and History FAQ      Why is there no goto       You can use exceptions to provide a    structured goto    that even works   across function calls  Many feel that exceptions can conveniently   emulate all reasonable uses of the    go    or    goto    constructs of C    Fortran  and other languages  For example    class label Exception   pass    declare a label  try              if condition  raise label      goto label         except label     where to goto     pass           This doesn   t allow you to jump into the middle of a loop  but that   s   usually considered an abuse of goto anyway  Use sparingly    It s very nice that this is even mentioned in the official FAQ  and that a nice solution sample is provided  I really like python because its community is treating even goto like this

User · Answer

I think while loop is alternate for the  quot goto Statement quot   Because after 3 6 goto loop is not working anymore  I also write an example of the while loop  str1    quot stop quot  while str1     quot back quot       var1   int input  quot  Enter Ist Number   quot        var2   int input  quot  Enter 2nd Number   quot        var3   print  quot  quot  quot   What is your next operation                       For Addition   Press And Enter    A                        For Muliplt    Press And Enter    M                        For Division   Press And Enter    D                        For Subtaction Press And Enter    S   quot  quot  quot        var4   str input  quot For operation press any number    quot        if var1    45  and  var2    3           print  quot 555 quot       elif var1    56  and  var2    9           print  quot 77 quot       elif var1    56  and  var2    6           print  quot 4 quot       else          if var4     quot A quot  or  quot a quot                print var1   var2          if var4     quot M quot  or  quot m quot                print var1   var2          if var4     quot D quot  or  quot d quot                print var1   var2          if var4     quot S quot  or  quot s quot                print var1 - var2       print  quot if you want to continue then type   stop  quot        str1   input   print  quot Strt again quot

User · Answer

A working version has been made  http   entrian com goto    Note  It was offered as an April Fool s joke   working though     Example 1  Breaking out from a deeply nested loop  from goto import goto  label  for i in range 1  10       for j in range 1  20           for k in range 1  30               print i  j  k             if k    3                  goto  end label  end print  Finished n    Needless to say  Yes its funny  but DONT use it

User · Answer

Though there isn t any code equivalent to goto label in Python  you could still get such functionality of goto label using loops     Lets take a code sample shown below where goto label can be used in a arbitrary language other than python   String str1    BACK   label1      print  Hello  this program contains goto code n       print  Now type BACK if you want the program to go back to the above line of code  Or press the ENTER key if you want the program to continue with further lines of code       str1   input    if str1     BACK                GoTo label1       print  Program will continue nBla bla bla    nBla bla bla    nBla bla bla        Now the same functionality of the above code sample can be achieved in python by using a while loop as shown below     str1    BACK   while str1     BACK           print  Hello  this is a python program containing python equivalent code for goto code n           print  Now type BACK if you want the program to go back to the above line of code  Or press the ENTER key if you want the program to continue with further lines of code           str1   input   print  Program will continue nBla bla bla    nBla bla bla    nBla bla bla

[python] Is there a label/goto in Python?

Python 2 & 3

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