The equivalent of a GOTO in python

Question

I am self teaching myself python 2 7  I  have some experience in using BATCH  which has a GOTO statement   How do I do that in python  For example  suppose I want to jump from line 5 to line 18   I realize there have been previous questions regarding this topic  but I have not found them sufficiently informative or  are too high level in python for my current understanding

User · Answer

Forgive me - I couldn t resist  -   def goto linenum       global line     line   linenum  line   1 while True      if line    1          response   raw input  yes or no             if response     yes               goto 2          elif response     no               goto 3          else              goto 100      elif line    2          print  Thank you for the yes           goto 20      elif line    3          print  Thank you for the no           goto 20      elif line    20          break     elif line    100          print  You re annoying me - answer the question           goto 1

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Disclaimer  I have been exposed to a significant amount of F77  The modern equivalent of goto  arguable  only my opinion  etc  is explicit exception handling   Edited to highlight the code reuse better   Pretend pseudocode in a fake python-like language with goto   def myfunc1 x      if x    0          goto LABEL1     return 1 x  def myfunc2 z      if z    0          goto LABEL1     return 1 z  myfunc1 0   myfunc2 0    LABEL1 print  Cannot divide by zero     Compared to python   def myfunc1 x       return 1 x  def myfunc2 y       return 1 y   try      myfunc1 0      myfunc2 0  except ZeroDivisionError      print  Cannot divide by zero    Explicit named exceptions are a significantly better way to deal with non-linear conditional branching

User · Answer

answer   None while True      answer   raw input  Do you like pie        if answer in   yes    no    break     print  That is not a yes or a no    Would give you what you want with no goto statement

User · Answer

Gotos are universally reviled in computer science and programming as they lead to very unstructured code   Python  like almost every programming language today  supports structured programming which controls flow using if then else  loop and subroutines   The key to thinking in a structured way is to understand how and why you are branching on code   For example  lets pretend Python had a goto and corresponding label statement shudder  Look at the following code  In it if a number is greater than or equal to 0 we print if it   number   input   if number  lt  0  goto negative if number   2    0     print  even  else     print  odd  goto end label  negative print  negative  label  end print  all done    If we want to know when a piece of code is executed  we need to carefully traceback in the program  and examine how a label was arrived at - which is something that can t really be done   For example  we can rewrite the above as   number   input   goto check  label  negative print  negative  goto end  label  check if number  lt  0  goto negative if number   2    0     print  even  else     print  odd  goto end  label  end print  all done    Here  there are two possible ways to arrive at the  end   and we can t know which one was chosen  As programs get large this kind of problem gets worse and results in spaghetti code  In comparison  below is how you would write this program in Python   number   input   if number  gt   0     if number   2    0         print  even     else         print  odd  else     print  negative  print  all done    I can look at a particular line of code  and know under what conditions it is met by tracing back the tree of if then else blocks it is in  For example  I know that the line print  odd  will be run when a   number  gt   0     True  and   number   2    0     False

User · Answer

I entirely agree that goto is poor poor coding  but no one has actually answered the question  There is in fact a goto module for Python  though it was released as an April fool joke and is not recommended to be used  it does work

User · Answer

There s no goto instruction in the Python programming language  You ll have to write your code in a structured way    But really  why do you want to use a goto  that s been considered harmful for decades  and any program you can think of can be written without using goto   Of course  there are some cases where an unconditional jump might be useful  but it s never mandatory  there will always exist a semantically equivalent  structured solution that doesn t need goto

[python] The equivalent of a GOTO in python

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