How to terminate a Python script

Question

I am aware of the die   command in PHP which exits a script early   How can I do this in Python

User · Answer

A simple way to terminate a Python script early is to use the built-in quit() function. There is no need to import any library, and it is efficient and simple.

Example:

#do stuff
if this == that:
  quit()

User · Answer

Another way is   raise SystemExit

User · Answer

While you should generally prefer sys exit because it is more  friendly  to other code  all it actually does is raise an exception   If you are sure that you need to exit a process immediately  and you might be inside of some exception handler which would catch SystemExit  there is another function - os  exit - which terminates immediately at the C level and does not perform any of the normal tear-down of the interpreter  for example  hooks registered with the  atexit  module are not executed

User · Answer

While you should generally prefer sys exit because it is more  friendly  to other code  all it actually does is raise an exception   If you are sure that you need to exit a process immediately  and you might be inside of some exception handler which would catch SystemExit  there is another function - os  exit - which terminates immediately at the C level and does not perform any of the normal tear-down of the interpreter  for example  hooks registered with the  atexit  module are not executed

User · Answer

My two cents   Python 3 8 1  Windows 10  64-bit   sys exit   does not work directly for me   I have several nexted loops   First I declare a boolean variable  which I call immediateExit   So  in the beginning of the program code I write   immediateExit   False   Then  starting from the most inner  nested  loop exception  I write               immediateExit   True             sys exit  CSV file corrupted 0      Then I go into the immediate continuation of the outer loop  and before anything else being executed by the code  I write       if immediateExit          sys exit  CSV file corrupted 1      Depending on the complexity  sometimes the above statement needs to be repeated also in except sections  etc       if immediateExit          sys exit  CSV file corrupted 1 5      The custom message is for my personal debugging  as well  as the numbers are for the same purpose - to see where the script really exits     CSV file corrupted 1 5     In my particular case I am processing a CSV file  which I do not want the software to touch  if the software detects it is corrupted  Therefore for me it is very important to exit the whole Python script immediately after detecting the possible corruption   And following the gradual sys exit-ing from all the loops I manage to do it   Full code   some changes were needed because it is proprietory code for internal tasks    immediateExit   False start date    1994 01 01  end date    1994 01 04  resumedDate   end date   end date in working days   False while not end date in working days      try          end day position   working days index end date           end date in working days   True     except ValueError    try statement from end date in workdays check         print current date and time            end date   input   gt  gt     is not in the list of working days  Change the date  YYYY MM DD     format end date           print  New end date     end date    n           continue       csv filename    test csv      csv headers    date rate brand n    not real headers  this is just for example     try          with open csv filename   r   as file              print      nOld file    found  Resuming the file by re-processing the last date lines  nThey shall be deleted and re-processed  n    n  format csv filename               last line   file readlines   -1              start date   last line split      0    assigning the start date to be the last like date              resumedDate   start date              if last line    csv headers                  pass             elif start date not in working days                  print      n n   file might be corrupted  Erase or edit the file to continue  n     format csv filename                   immediateExit   True                 sys exit  CSV file corrupted 0                else                  start date   last line split      0    assigning the start date to be the last like date                  print   nLast date    start date                  file seek 0    setting the cursor at the beginnning of the file                 lines   file readlines     reading the file contents into a list                 count   0   nr  of lines with last date                 for line in lines   cycling through the lines of the file                     if line split      0     start date    cycle for counting the lines with last date in it                          count   count   1         if immediateExit              sys exit  CSV file corrupted 1            for iter in range count     removing the lines with last date             lines pop           print   n   lines removed from date     in    file  format count  start date  csv filename              if immediateExit              sys exit  CSV file corrupted 1 2            with open csv filename   w   as file              print   nFile   csv filename   open for writing               file writelines lines               print   nRemoving   count   lines from   csv filename           fileExists   True      except          if immediateExit              sys exit  CSV file corrupted 1 5            with open csv filename   w   as file              file write csv headers              fileExists   False     if immediateExit          sys exit  CSV file corrupted 2

User · Answer

In Python 3 5  I tried to incorporate similar code without use of modules  e g  sys  Biopy  other than what s built-in to stop the script and print an error message to my users  Here s my example      My example  if  ATG  in my DNA           lt Do something  amp  proceed    gt  else       print  Start codon is missing  Check your DNA sequence        exit      as most folks said above   Later on  I found it is more succinct to just throw an error      My example revised  if  ATG  in my DNA           lt Do something  amp  proceed    gt  else       raise ValueError  Start codon is missing  Check your DNA sequence

User · Answer

Another way is   raise SystemExit

User · Answer

You can also use simply exit     Keep in mind that sys exit    exit    quit    and os  exit 0  kill the Python interpreter  Therefore  if it appears in a script called from another script by execfile    it stops execution of both scripts    See  Stop execution of a script called with execfile  to avoid this

User · Answer

I m a total novice but surely this is cleaner and more controlled  def main        try          Answer   1 0         print  Answer     except          print  Program terminated          return     print  You wont see this   if   name         main          main             Program terminated   than  import sys def main        try          Answer   1 0         print  Answer     except          print  Program terminated          sys exit       print  You wont see this   if   name         main          main                  Program terminated Traceback  most recent call last     File  Z  Directory testdieprogram py   line 12  in          main     File  Z  Directory testdieprogram py   line 8  in main         sys exit   SystemExit      Edit  The point being that the program ends smoothly and peacefully  rather than  I VE STOPPED

User · Answer

A simple way to terminate a Python script early is to use the built-in quit() function. There is no need to import any library, and it is efficient and simple.

Example:

#do stuff
if this == that:
  quit()

User · Answer

from sys import exit exit     As a parameter you can pass an exit code  which will be returned to OS  Default is 0

User · Answer

Another way is   raise SystemExit

User · Answer

import sys sys exit    details from the sys module documentation   sys exit  arg      Exit from Python  This is implemented by raising the SystemExit exception  so cleanup actions specified by finally clauses of try statements are honored  and it is possible to intercept the exit attempt at an outer level    The optional argument arg can be an integer giving the exit status  defaulting to zero   or another type of object  If it is an integer  zero is considered    successful termination    and any nonzero value is considered    abnormal termination    by shells and the like  Most systems require it to be in the range 0-127  and produce undefined results otherwise  Some systems have a convention for assigning specific meanings to specific exit codes  but these are generally underdeveloped  Unix programs generally use 2 for command line syntax errors and 1 for all other kind of errors  If another type of object is passed  None is equivalent to passing zero  and any other object is printed to stderr and results in an exit code of 1  In particular  sys exit  quot some error message quot   is a quick way to exit a program when an error occurs    Since exit   ultimately    only    raises an exception  it will only exit the process when called from the main thread  and the exception is not intercepted    Note that this is the  nice  way to exit    glyphtwistedmatrix below points out that if you want a  hard exit   you can use os  exit  errorcode    though it s likely os-specific to some extent  it might not take an errorcode under windows  for example   and it definitely is less friendly since it doesn t let the interpreter do any cleanup before the process dies   On the other hand  it does kill the entire process  including all running threads  while sys exit    as it says in the docs  only exits if called from the main thread  with no other threads running

User · Answer

import sys sys exit    details from the sys module documentation   sys exit  arg      Exit from Python  This is implemented by raising the SystemExit exception  so cleanup actions specified by finally clauses of try statements are honored  and it is possible to intercept the exit attempt at an outer level    The optional argument arg can be an integer giving the exit status  defaulting to zero   or another type of object  If it is an integer  zero is considered    successful termination    and any nonzero value is considered    abnormal termination    by shells and the like  Most systems require it to be in the range 0-127  and produce undefined results otherwise  Some systems have a convention for assigning specific meanings to specific exit codes  but these are generally underdeveloped  Unix programs generally use 2 for command line syntax errors and 1 for all other kind of errors  If another type of object is passed  None is equivalent to passing zero  and any other object is printed to stderr and results in an exit code of 1  In particular  sys exit  quot some error message quot   is a quick way to exit a program when an error occurs    Since exit   ultimately    only    raises an exception  it will only exit the process when called from the main thread  and the exception is not intercepted    Note that this is the  nice  way to exit    glyphtwistedmatrix below points out that if you want a  hard exit   you can use os  exit  errorcode    though it s likely os-specific to some extent  it might not take an errorcode under windows  for example   and it definitely is less friendly since it doesn t let the interpreter do any cleanup before the process dies   On the other hand  it does kill the entire process  including all running threads  while sys exit    as it says in the docs  only exits if called from the main thread  with no other threads running

User · Answer

I ve just found out that when writing a multithreadded app  raise SystemExit and sys exit   both kills only the running thread  On the other hand  os  exit   exits the whole process  This was discussed in  Why does sys exit   not exit when called inside a thread in Python     The example below has 2 threads  Kenny and Cartman  Cartman is supposed to live forever  but Kenny is called recursively and should die after 3 seconds   recursive calling is not the best way  but I had other reasons   If we also want Cartman to die when Kenny dies  Kenny should go away with os  exit  otherwise  only Kenny will die and Cartman will live forever   import threading import time import sys import os  def kenny num 0       if num  gt  3            print  Kenny dies now                raise SystemExit  Kenny will die  but Cartman will live forever           sys exit 1   Same as above          print  Kenny dies and also kills Cartman            os  exit 1      while True          print  Kenny lives   0   format num           time sleep 1          num    1         kenny num   def cartman        i   0     while True          print  Cartman lives   0   format i           i    1         time sleep 1   if   name         main         daemon kenny   threading Thread name  kenny   target kenny      daemon cartman   threading Thread name  cartman   target cartman      daemon kenny setDaemon True      daemon cartman setDaemon True       daemon kenny start       daemon cartman start       daemon kenny join       daemon cartman join

User · Answer

While you should generally prefer sys exit because it is more  friendly  to other code  all it actually does is raise an exception   If you are sure that you need to exit a process immediately  and you might be inside of some exception handler which would catch SystemExit  there is another function - os  exit - which terminates immediately at the C level and does not perform any of the normal tear-down of the interpreter  for example  hooks registered with the  atexit  module are not executed

User · Answer

In Python 3 5  I tried to incorporate similar code without use of modules  e g  sys  Biopy  other than what s built-in to stop the script and print an error message to my users  Here s my example      My example  if  ATG  in my DNA           lt Do something  amp  proceed    gt  else       print  Start codon is missing  Check your DNA sequence        exit      as most folks said above   Later on  I found it is more succinct to just throw an error      My example revised  if  ATG  in my DNA           lt Do something  amp  proceed    gt  else       raise ValueError  Start codon is missing  Check your DNA sequence

User · Answer

Another way is   raise SystemExit

User · Answer

from sys import exit exit     As a parameter you can pass an exit code  which will be returned to OS  Default is 0

User · Answer

I m a total novice but surely this is cleaner and more controlled  def main        try          Answer   1 0         print  Answer     except          print  Program terminated          return     print  You wont see this   if   name         main          main             Program terminated   than  import sys def main        try          Answer   1 0         print  Answer     except          print  Program terminated          sys exit       print  You wont see this   if   name         main          main                  Program terminated Traceback  most recent call last     File  Z  Directory testdieprogram py   line 12  in          main     File  Z  Directory testdieprogram py   line 8  in main         sys exit   SystemExit      Edit  The point being that the program ends smoothly and peacefully  rather than  I VE STOPPED

User · Answer

from sys import exit exit     As a parameter you can pass an exit code  which will be returned to OS  Default is 0

User · Answer

My two cents   Python 3 8 1  Windows 10  64-bit   sys exit   does not work directly for me   I have several nexted loops   First I declare a boolean variable  which I call immediateExit   So  in the beginning of the program code I write   immediateExit   False   Then  starting from the most inner  nested  loop exception  I write               immediateExit   True             sys exit  CSV file corrupted 0      Then I go into the immediate continuation of the outer loop  and before anything else being executed by the code  I write       if immediateExit          sys exit  CSV file corrupted 1      Depending on the complexity  sometimes the above statement needs to be repeated also in except sections  etc       if immediateExit          sys exit  CSV file corrupted 1 5      The custom message is for my personal debugging  as well  as the numbers are for the same purpose - to see where the script really exits     CSV file corrupted 1 5     In my particular case I am processing a CSV file  which I do not want the software to touch  if the software detects it is corrupted  Therefore for me it is very important to exit the whole Python script immediately after detecting the possible corruption   And following the gradual sys exit-ing from all the loops I manage to do it   Full code   some changes were needed because it is proprietory code for internal tasks    immediateExit   False start date    1994 01 01  end date    1994 01 04  resumedDate   end date   end date in working days   False while not end date in working days      try          end day position   working days index end date           end date in working days   True     except ValueError    try statement from end date in workdays check         print current date and time            end date   input   gt  gt     is not in the list of working days  Change the date  YYYY MM DD     format end date           print  New end date     end date    n           continue       csv filename    test csv      csv headers    date rate brand n    not real headers  this is just for example     try          with open csv filename   r   as file              print      nOld file    found  Resuming the file by re-processing the last date lines  nThey shall be deleted and re-processed  n    n  format csv filename               last line   file readlines   -1              start date   last line split      0    assigning the start date to be the last like date              resumedDate   start date              if last line    csv headers                  pass             elif start date not in working days                  print      n n   file might be corrupted  Erase or edit the file to continue  n     format csv filename                   immediateExit   True                 sys exit  CSV file corrupted 0                else                  start date   last line split      0    assigning the start date to be the last like date                  print   nLast date    start date                  file seek 0    setting the cursor at the beginnning of the file                 lines   file readlines     reading the file contents into a list                 count   0   nr  of lines with last date                 for line in lines   cycling through the lines of the file                     if line split      0     start date    cycle for counting the lines with last date in it                          count   count   1         if immediateExit              sys exit  CSV file corrupted 1            for iter in range count     removing the lines with last date             lines pop           print   n   lines removed from date     in    file  format count  start date  csv filename              if immediateExit              sys exit  CSV file corrupted 1 2            with open csv filename   w   as file              print   nFile   csv filename   open for writing               file writelines lines               print   nRemoving   count   lines from   csv filename           fileExists   True      except          if immediateExit              sys exit  CSV file corrupted 1 5            with open csv filename   w   as file              file write csv headers              fileExists   False     if immediateExit          sys exit  CSV file corrupted 2

User · Answer

I ve just found out that when writing a multithreadded app  raise SystemExit and sys exit   both kills only the running thread  On the other hand  os  exit   exits the whole process  This was discussed in  Why does sys exit   not exit when called inside a thread in Python     The example below has 2 threads  Kenny and Cartman  Cartman is supposed to live forever  but Kenny is called recursively and should die after 3 seconds   recursive calling is not the best way  but I had other reasons   If we also want Cartman to die when Kenny dies  Kenny should go away with os  exit  otherwise  only Kenny will die and Cartman will live forever   import threading import time import sys import os  def kenny num 0       if num  gt  3            print  Kenny dies now                raise SystemExit  Kenny will die  but Cartman will live forever           sys exit 1   Same as above          print  Kenny dies and also kills Cartman            os  exit 1      while True          print  Kenny lives   0   format num           time sleep 1          num    1         kenny num   def cartman        i   0     while True          print  Cartman lives   0   format i           i    1         time sleep 1   if   name         main         daemon kenny   threading Thread name  kenny   target kenny      daemon cartman   threading Thread name  cartman   target cartman      daemon kenny setDaemon True      daemon cartman setDaemon True       daemon kenny start       daemon cartman start       daemon kenny join       daemon cartman join

User · Answer

from sys import exit exit     As a parameter you can pass an exit code  which will be returned to OS  Default is 0

User · Answer

import sys sys exit    details from the sys module documentation   sys exit  arg      Exit from Python  This is implemented by raising the SystemExit exception  so cleanup actions specified by finally clauses of try statements are honored  and it is possible to intercept the exit attempt at an outer level    The optional argument arg can be an integer giving the exit status  defaulting to zero   or another type of object  If it is an integer  zero is considered    successful termination    and any nonzero value is considered    abnormal termination    by shells and the like  Most systems require it to be in the range 0-127  and produce undefined results otherwise  Some systems have a convention for assigning specific meanings to specific exit codes  but these are generally underdeveloped  Unix programs generally use 2 for command line syntax errors and 1 for all other kind of errors  If another type of object is passed  None is equivalent to passing zero  and any other object is printed to stderr and results in an exit code of 1  In particular  sys exit  quot some error message quot   is a quick way to exit a program when an error occurs    Since exit   ultimately    only    raises an exception  it will only exit the process when called from the main thread  and the exception is not intercepted    Note that this is the  nice  way to exit    glyphtwistedmatrix below points out that if you want a  hard exit   you can use os  exit  errorcode    though it s likely os-specific to some extent  it might not take an errorcode under windows  for example   and it definitely is less friendly since it doesn t let the interpreter do any cleanup before the process dies   On the other hand  it does kill the entire process  including all running threads  while sys exit    as it says in the docs  only exits if called from the main thread  with no other threads running

User · Answer

You can also use simply exit     Keep in mind that sys exit    exit    quit    and os  exit 0  kill the Python interpreter  Therefore  if it appears in a script called from another script by execfile    it stops execution of both scripts    See  Stop execution of a script called with execfile  to avoid this

User · Answer

import sys sys exit    details from the sys module documentation   sys exit  arg      Exit from Python  This is implemented by raising the SystemExit exception  so cleanup actions specified by finally clauses of try statements are honored  and it is possible to intercept the exit attempt at an outer level    The optional argument arg can be an integer giving the exit status  defaulting to zero   or another type of object  If it is an integer  zero is considered    successful termination    and any nonzero value is considered    abnormal termination    by shells and the like  Most systems require it to be in the range 0-127  and produce undefined results otherwise  Some systems have a convention for assigning specific meanings to specific exit codes  but these are generally underdeveloped  Unix programs generally use 2 for command line syntax errors and 1 for all other kind of errors  If another type of object is passed  None is equivalent to passing zero  and any other object is printed to stderr and results in an exit code of 1  In particular  sys exit  quot some error message quot   is a quick way to exit a program when an error occurs    Since exit   ultimately    only    raises an exception  it will only exit the process when called from the main thread  and the exception is not intercepted    Note that this is the  nice  way to exit    glyphtwistedmatrix below points out that if you want a  hard exit   you can use os  exit  errorcode    though it s likely os-specific to some extent  it might not take an errorcode under windows  for example   and it definitely is less friendly since it doesn t let the interpreter do any cleanup before the process dies   On the other hand  it does kill the entire process  including all running threads  while sys exit    as it says in the docs  only exits if called from the main thread  with no other threads running

User · Answer

While you should generally prefer sys exit because it is more  friendly  to other code  all it actually does is raise an exception   If you are sure that you need to exit a process immediately  and you might be inside of some exception handler which would catch SystemExit  there is another function - os  exit - which terminates immediately at the C level and does not perform any of the normal tear-down of the interpreter  for example  hooks registered with the  atexit  module are not executed

[python] How to terminate a Python script

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