Python exit commands - why so many and when should each be used

Question

It seems that python supports many different commands to stop script execution The choices I ve found are   quit    exit    sys exit    os  exit     Have I missed any  What s the difference between them  When would you use each

User · Answer

sys exit is the canonical way to exit    Internally sys exit just raises SystemExit  However  calling sys exitis more idiomatic than raising SystemExit directly   os exit is a low-level system call that exits directly without calling any cleanup handlers   quit and exit exist only to provide an easy way out of the Python prompt  This is for new users or users who accidentally entered the Python prompt  and don t want to know the right syntax  They are likely to try typing exit or quit  While this will not exit the interpreter  it at least issues a message that tells them a way out    gt  gt  gt  exit Use exit   or Ctrl-D  i e  EOF  to exit  gt  gt  gt  exit       This is essentially just a hack that utilizes the fact that the interpreter prints the   repr   of any expression that you enter at the prompt

User · Answer

Let me give some information on them    quit   simply raises the SystemExit exception     Furthermore  if you print it  it will give a message    gt  gt  gt  print  quit  Use quit   or Ctrl-Z plus Return to exit  gt  gt  gt    This functionality was included to help people who do not know Python   After all  one of the most likely things a newbie will try to exit Python is typing in quit   Nevertheless  quit should not be used in production code   This is because it only works if the site module is loaded   Instead  this function should only be used in the interpreter  exit   is an alias for quit  or vice-versa    They exist together simply to make Python more user-friendly     Furthermore  it too gives a message when printed    gt  gt  gt  print  exit  Use exit   or Ctrl-Z plus Return to exit  gt  gt  gt    However  like quit  exit is considered bad to use in production code and should be reserved for use in the interpreter   This is because it too relies on the site module  sys exit   also raises the SystemExit exception   This means that it is the same as quit and exit in that respect     Unlike those two however  sys exit is considered good to use in production code   This is because the sys module will always be there  os  exit   exits the program without calling cleanup handlers  flushing stdio buffers  etc   Thus  it is not a standard way to exit and should only be used in special cases   The most common of these is in the child process es  created by os fork   Note that  of the four methods given  only this one is unique in what it does    Summed up  all four methods exit the program   However  the first two are considered bad to use in production code and the last is a non-standard  dirty way that is only used in special scenarios   So  if you want to exit a program normally  go with the third method  sys exit     Or  even better in my opinion  you can just do directly what sys exit does behind the scenes and run   raise SystemExit   This way  you do not need to import sys first     However  this choice is simply one on style and is purely up to you

User · Answer

Different Means of Exiting  os  exit      Exit the process without calling the cleanup handlers      exit 0     a clean exit without any errors   problems      exit 1     There was some issue   error   problem and that is why the program is exiting      sys exit      When the system and python shuts down  it means less memory is being used after the program is run      quit      Closes the python file      Summary  Basically they all do the same thing  however  it also depends on what you are doing it for   I don t think you left anything out and I would recommend getting used to quit   or exit     You would use sys exit   and os  exit   mainly if you are using big files or are using python to control terminal   Otherwise mainly use exit   or quit

User · Answer

The functions  quit    exit    and sys exit   function in the same way  they raise the SystemExit exception   So there is no real difference  except that sys exit   is always available but exit   and quit   are only available if the site module is imported   The os  exit   function is special  it exits immediately without calling any cleanup functions  it doesn t flush buffers  for example    This is designed for highly specialized use cases    basically  only in the child after an os fork   call   Conclusion   Use exit   or quit   in the REPL  Use sys exit   in scripts  or raise SystemExit   if you prefer  Use os  exit   for child processes to exit after a call to os fork      All of these can be called without arguments  or you can specify the exit status  e g   exit 1  or raise SystemExit 1  to exit with status 1  Note that portable programs are limited to exit status codes in the range 0-255  if you raise SystemExit 256  on many systems this will get truncated and your process will actually exit with status 0   Footnotes    Actually  quit   and exit   are callable instance objects  but I think it s okay to call them functions

[python] Python exit commands - why so many and when should each be used?

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