How can I check for Python version in a program that uses new language features

Question

If I have a Python script that requires at least a particular version of Python  what is the correct way to fail gracefully when an earlier version of Python is used to launch the script   How do I get control early enough to issue an error message and exit   For example  I have a program that uses the ternery operator  new in 2 5  and  with  blocks  new in 2 6    I wrote a simple little interpreter-version checker routine which is the first thing the script would call     except it doesn t get that far  Instead  the script fails during python compilation  before my routines are even called  Thus the user of the script sees some very obscure synax error tracebacks - which pretty much require an expert to deduce that it is simply the case of running the wrong version of Python   I know how to check the version of Python  The issue is that some syntax is illegal in older versions of Python  Consider this program   import sys if sys version info  lt   2  4       raise  must use python 2 5 or greater  else        syntax error in 2 4  ok in 2 5     x   1 if True else 2     print x   When run under 2 4  I want this result      bin python2 4 tern py  must use python 2 5 or greater   and not this result       bin python2 4 tern py    File  tern py   line 5     x   1 if True else 2              SyntaxError  invalid syntax    Channeling for a coworker

User · Answer

How about this   import sys  def testPyVer reqver     if float sys version  3    gt   reqver      return 1   else      return 0   blah blah blah  more code  if testPyVer 3 0     1     do stuff else     print python requirement  exit statement

User · Answer

You can test using eval   try    eval  1 if True else 2   except SyntaxError      doesn t have ternary   Also  with is available in Python 2 5  just add from   future   import with statement   EDIT  to get control early enough  you could split it into different  py files and check compatibility in the main file before importing  e g  in   init   py in a package        init   py    Check compatibility try    eval  1 if True else 2   except SyntaxError    raise ImportError  requires ternary support      import from another module from impl import

User · Answer

I think the best way is to test for functionality rather than versions  In some cases  this is trivial  not so in others   eg   try         Do stuff except     Features weren t found        Do stuff for older versions    As long as you re specific in enough in using the try except blocks  you can cover most of your bases

User · Answer

Try    import platform platform python version     Should give you a string like  2 3 1   If this is not exactly waht you want there is a rich set of data available through the  platform  build-in  What you want should be in there somewhere

User · Answer

Try    import platform platform python version     Should give you a string like  2 3 1   If this is not exactly waht you want there is a rich set of data available through the  platform  build-in  What you want should be in there somewhere

User · Answer

You can test using eval   try    eval  1 if True else 2   except SyntaxError      doesn t have ternary   Also  with is available in Python 2 5  just add from   future   import with statement   EDIT  to get control early enough  you could split it into different  py files and check compatibility in the main file before importing  e g  in   init   py in a package        init   py    Check compatibility try    eval  1 if True else 2   except SyntaxError    raise ImportError  requires ternary support      import from another module from impl import

User · Answer

Sets became part of the core language in Python 2 4  in order to stay backwards compatible  I did this back then  which will work for you as well   if sys version info  lt   2  4       from sets import Set as set

User · Answer

import sys       prints whether python is version 3 or not python version   sys version info major if python version    3      print  is python 3   else      print  not python 3

User · Answer

You can check with sys hexversion or sys version info   sys hexversion isn t very human-friendly because it s a hexadecimal number  sys version info is a tuple  so it s more human-friendly   Check for Python 3 6 or newer with sys hexversion   import sys  time if sys hexversion  lt  0x30600F0      print  You need Python 3 6 or greater        for   in range 1  5   time sleep 1      exit     Check for Python 3 6 or newer with sys version info   import sys  time if sys version info 0   lt  3 and sys version info 1   lt  6      print  You need Python 3 6 or greater        for   in range 1  5   time sleep 1      exit     sys version info is more human-friendly  but takes more characters  I would reccomend sys hexversion  even though it is less human-friendly   I hope this helped you

User · Answer

Probably the best way to do do this version comparison is to use the sys hexversion  This is important because comparing version tuples will not give you the desired result in all python versions   import sys if sys hexversion  lt  0x02060000      print  yep   else      print  oops

User · Answer

As noted above  syntax errors occur at compile time  not at run time   While Python is an  interpreted language   Python code is not actually directly interpreted  it s compiled to byte code  which is then interpreted   There is a compile step that happens when a module is imported  if there is no already-compiled version available in the form of a  pyc or  pyd file  and that s when you re getting your error  not  quite exactly  when your code is running     You can put off the compile step and make it happen at run time for a single line of code  if you want to  by using eval  as noted above  but I personally prefer to avoid doing that  because it causes Python to perform potentially unnecessary run-time compilation  for one thing  and for another  it creates what to me feels like code clutter    If you want  you can generate code that generates code that generates code - and have an absolutely fabulous time modifying and debugging that in 6 months from now    So what I would recommend instead is something more like this   import sys if sys hexversion  lt  0x02060000      from my module 2 5 import thisFunc  thatFunc  theOtherFunc else      from my module import thisFunc  thatFunc  theOtherFunc      which I would do even if I only had one function that used newer syntax and it was very short    In fact I would take every reasonable measure to minimize the number and size of such functions   I might even write a function like ifTrueAElseB cond  a  b  with that single line of syntax in it    Another thing that might be worth pointing out  that I m a little amazed no one has pointed out yet  is that while earlier versions of Python did not support code like  value    yes  if MyVarIsTrue else  no      it did support code like  value   MyVarIsTrue and  yes  or  no    That was the old way of writing ternary expressions   I don t have Python 3 installed yet  but as far as I know  that  old  way still works to this day  so you can decide for yourself whether or not it s worth it to conditionally use the new syntax  if you need to support the use of older versions of Python

User · Answer

I m expanding on akhan s excellent answer  which prints a helpful message before the Python script is even compiled   If you want to ensure that the script is being run with Python 3 6 or newer  add these two lines to the top of your Python script      bin sh     python3 -c  import sys  sys exit sys version info  lt   3  6     amp  amp  exec python3 -u --   0    1        echo  This script requires Python 3 6 or newer    exit 1          Note   The second line starts with four single-quotes and ends with three single-quotes   This may look strange  but it is not a typo    The advantage of this solution is that code like print f Hello   name     won t cause a SyntaxError if a Python version older than 3 6 is used   You ll see this helpful message instead   This script requires Python 3 6 or newer    Of course  this solution only works on Unix-like shells  and only when the script is invoked directly  such as    script py   and with the proper eXecute permission bits set

User · Answer

I think the best way is to test for functionality rather than versions  In some cases  this is trivial  not so in others   eg   try         Do stuff except     Features weren t found        Do stuff for older versions    As long as you re specific in enough in using the try except blocks  you can cover most of your bases

User · Answer

The problem is quite simple  You checked if the version was less than 2 4  not less than or equal to  So if the Python version is 2 4  it s not less than 2 4  What you should have had was       if sys version info    lt      2  4       not      if sys version info  lt   2  4

User · Answer

As noted above  syntax errors occur at compile time  not at run time   While Python is an  interpreted language   Python code is not actually directly interpreted  it s compiled to byte code  which is then interpreted   There is a compile step that happens when a module is imported  if there is no already-compiled version available in the form of a  pyc or  pyd file  and that s when you re getting your error  not  quite exactly  when your code is running     You can put off the compile step and make it happen at run time for a single line of code  if you want to  by using eval  as noted above  but I personally prefer to avoid doing that  because it causes Python to perform potentially unnecessary run-time compilation  for one thing  and for another  it creates what to me feels like code clutter    If you want  you can generate code that generates code that generates code - and have an absolutely fabulous time modifying and debugging that in 6 months from now    So what I would recommend instead is something more like this   import sys if sys hexversion  lt  0x02060000      from my module 2 5 import thisFunc  thatFunc  theOtherFunc else      from my module import thisFunc  thatFunc  theOtherFunc      which I would do even if I only had one function that used newer syntax and it was very short    In fact I would take every reasonable measure to minimize the number and size of such functions   I might even write a function like ifTrueAElseB cond  a  b  with that single line of syntax in it    Another thing that might be worth pointing out  that I m a little amazed no one has pointed out yet  is that while earlier versions of Python did not support code like  value    yes  if MyVarIsTrue else  no      it did support code like  value   MyVarIsTrue and  yes  or  no    That was the old way of writing ternary expressions   I don t have Python 3 installed yet  but as far as I know  that  old  way still works to this day  so you can decide for yourself whether or not it s worth it to conditionally use the new syntax  if you need to support the use of older versions of Python

User · Answer

Have a wrapper around your program that does the following   import sys  req version    2 5  cur version   sys version info  if cur version  gt   req version     import myApp    myApp run   else     print  Your Python interpreter is too old  Please consider upgrading     You can also consider using sys version    if you plan to encounter people who are using pre-2 0 Python interpreters  but then you have some regular expressions to do   And there might be more elegant ways to do this

User · Answer

You can test using eval   try    eval  1 if True else 2   except SyntaxError      doesn t have ternary   Also  with is available in Python 2 5  just add from   future   import with statement   EDIT  to get control early enough  you could split it into different  py files and check compatibility in the main file before importing  e g  in   init   py in a package        init   py    Check compatibility try    eval  1 if True else 2   except SyntaxError    raise ImportError  requires ternary support      import from another module from impl import

User · Answer

import sys sys version   will be getting answer like this       2 7 6  default  Oct 26 2016  20 30 19   n GCC 4 8 4     here 2 7 6 is version

User · Answer

You can test using eval   try    eval  1 if True else 2   except SyntaxError      doesn t have ternary   Also  with is available in Python 2 5  just add from   future   import with statement   EDIT  to get control early enough  you could split it into different  py files and check compatibility in the main file before importing  e g  in   init   py in a package        init   py    Check compatibility try    eval  1 if True else 2   except SyntaxError    raise ImportError  requires ternary support      import from another module from impl import

User · Answer

Have a wrapper around your program that does the following   import sys  req version    2 5  cur version   sys version info  if cur version  gt   req version     import myApp    myApp run   else     print  Your Python interpreter is too old  Please consider upgrading     You can also consider using sys version    if you plan to encounter people who are using pre-2 0 Python interpreters  but then you have some regular expressions to do   And there might be more elegant ways to do this

User · Answer

Answer from Nykakin at AskUbuntu    You can also check Python version from code itself using platform module from standard library   There are two functions    platform python version    returns string   platform python version tuple    returns tuple       The Python code     Create a file for example  version py    Easy method to check version   import platform  print platform python version    print platform python version tuple      You can also use the eval method   try    eval  1 if True else 2   except SyntaxError    raise ImportError  requires ternary support       Run the Python file in a command line     python version py  2 7 11   2    7    11     The output of Python with CGI via a WAMP Server on Windows 10       Helpful resources   https   askubuntu com questions 505081 what-version-of-python-do-i-have

User · Answer

The problem is quite simple  You checked if the version was less than 2 4  not less than or equal to  So if the Python version is 2 4  it s not less than 2 4  What you should have had was       if sys version info    lt      2  4       not      if sys version info  lt   2  4

User · Answer

You can check with sys hexversion or sys version info   sys hexversion isn t very human-friendly because it s a hexadecimal number  sys version info is a tuple  so it s more human-friendly   Check for Python 3 6 or newer with sys hexversion   import sys  time if sys hexversion  lt  0x30600F0      print  You need Python 3 6 or greater        for   in range 1  5   time sleep 1      exit     Check for Python 3 6 or newer with sys version info   import sys  time if sys version info 0   lt  3 and sys version info 1   lt  6      print  You need Python 3 6 or greater        for   in range 1  5   time sleep 1      exit     sys version info is more human-friendly  but takes more characters  I would reccomend sys hexversion  even though it is less human-friendly   I hope this helped you

User · Answer

Sets became part of the core language in Python 2 4  in order to stay backwards compatible  I did this back then  which will work for you as well   if sys version info  lt   2  4       from sets import Set as set

User · Answer

How about this   import sys  def testPyVer reqver     if float sys version  3    gt   reqver      return 1   else      return 0   blah blah blah  more code  if testPyVer 3 0     1     do stuff else     print python requirement  exit statement

User · Answer

Probably the best way to do do this version comparison is to use the sys hexversion  This is important because comparing version tuples will not give you the desired result in all python versions   import sys if sys hexversion  lt  0x02060000      print  yep   else      print  oops

User · Answer

I think the best way is to test for functionality rather than versions  In some cases  this is trivial  not so in others   eg   try         Do stuff except     Features weren t found        Do stuff for older versions    As long as you re specific in enough in using the try except blocks  you can cover most of your bases

User · Answer

Answer from Nykakin at AskUbuntu    You can also check Python version from code itself using platform module from standard library   There are two functions    platform python version    returns string   platform python version tuple    returns tuple       The Python code     Create a file for example  version py    Easy method to check version   import platform  print platform python version    print platform python version tuple      You can also use the eval method   try    eval  1 if True else 2   except SyntaxError    raise ImportError  requires ternary support       Run the Python file in a command line     python version py  2 7 11   2    7    11     The output of Python with CGI via a WAMP Server on Windows 10       Helpful resources   https   askubuntu com questions 505081 what-version-of-python-do-i-have

User · Answer

For standalone python scripts  the following module docstring trick to enforce a python version  here v2 7 x  works  tested on  nix       bin sh     python -V 2 gt  amp 1   grep -q 2 7  amp  amp  exec python -u --   0    1        echo  python 2 7 x missing   exit 1        import sys         This should handle missing python executable as well but has a dependency on grep  See here for background

User · Answer

I m expanding on akhan s excellent answer  which prints a helpful message before the Python script is even compiled   If you want to ensure that the script is being run with Python 3 6 or newer  add these two lines to the top of your Python script      bin sh     python3 -c  import sys  sys exit sys version info  lt   3  6     amp  amp  exec python3 -u --   0    1        echo  This script requires Python 3 6 or newer    exit 1          Note   The second line starts with four single-quotes and ends with three single-quotes   This may look strange  but it is not a typo    The advantage of this solution is that code like print f Hello   name     won t cause a SyntaxError if a Python version older than 3 6 is used   You ll see this helpful message instead   This script requires Python 3 6 or newer    Of course  this solution only works on Unix-like shells  and only when the script is invoked directly  such as    script py   and with the proper eXecute permission bits set

User · Answer

Have a wrapper around your program that does the following   import sys  req version    2 5  cur version   sys version info  if cur version  gt   req version     import myApp    myApp run   else     print  Your Python interpreter is too old  Please consider upgrading     You can also consider using sys version    if you plan to encounter people who are using pre-2 0 Python interpreters  but then you have some regular expressions to do   And there might be more elegant ways to do this

User · Answer

Try    import platform platform python version     Should give you a string like  2 3 1   If this is not exactly waht you want there is a rich set of data available through the  platform  build-in  What you want should be in there somewhere

User · Answer

Put the following at the very top of your file   import sys  if float sys version split   0   3    lt  2 7      print  Python 2 7 or higher required to run this code      sys version split   0      detected  exiting       exit 1    Then continue on with the normal Python code   import     import     other code

User · Answer

Although the question is  How do I get control early enough to issue an error message and exit   The question that I answer is  How do I get control early enough to issue an error message before starting the app   I can answer it a lot differently then the other posts  Seems answers so far are trying to solve your question from within Python   I say  do version checking before launching Python  I see your path is Linux or unix  However I can only offer you a Windows script  I image adapting it to linux scripting syntax wouldn t be too hard   Here is the DOS script with version 2 7    ECHO OFF REM see http   ss64 com nt for f html FOR  F  tokens 1 2    G IN    python exe -V 2 gt  amp 1    DO ECHO   H   find  2 7   gt  Nul IF NOT ErrorLevel 1 GOTO Python27 ECHO must use python2 7 or greater GOTO EOF  Python27 python exe tern py GOTO EOF  EOF   This does not run any part of your application and therefore will not raise a Python Exception  It does not create any temp file or add any OS environment variables  And it doesn t end your app to an exception due to different version syntax rules  That s three less possible security points of access   The FOR  F line is the key   FOR  F  tokens 1 2    G IN    python exe -V 2 gt  amp 1    DO ECHO   H   find  2 7   gt  Nul   For multiple python version check check out url  http   www fpschultze de modules smartfaq faq php faqid 17  And my hack version    MS script  Python version check prelaunch of Python module  http   pastebin com aAuJ91FQ

User · Answer

Although the question is  How do I get control early enough to issue an error message and exit   The question that I answer is  How do I get control early enough to issue an error message before starting the app   I can answer it a lot differently then the other posts  Seems answers so far are trying to solve your question from within Python   I say  do version checking before launching Python  I see your path is Linux or unix  However I can only offer you a Windows script  I image adapting it to linux scripting syntax wouldn t be too hard   Here is the DOS script with version 2 7    ECHO OFF REM see http   ss64 com nt for f html FOR  F  tokens 1 2    G IN    python exe -V 2 gt  amp 1    DO ECHO   H   find  2 7   gt  Nul IF NOT ErrorLevel 1 GOTO Python27 ECHO must use python2 7 or greater GOTO EOF  Python27 python exe tern py GOTO EOF  EOF   This does not run any part of your application and therefore will not raise a Python Exception  It does not create any temp file or add any OS environment variables  And it doesn t end your app to an exception due to different version syntax rules  That s three less possible security points of access   The FOR  F line is the key   FOR  F  tokens 1 2    G IN    python exe -V 2 gt  amp 1    DO ECHO   H   find  2 7   gt  Nul   For multiple python version check check out url  http   www fpschultze de modules smartfaq faq php faqid 17  And my hack version    MS script  Python version check prelaunch of Python module  http   pastebin com aAuJ91FQ

User · Answer

I just found this question after a quick search whilst trying to solve the problem myself and I ve come up with a hybrid based on a few of the suggestions above   I like DevPlayer s idea of using a wrapper script  but the downside is that you end up maintaining multiple wrappers for different OSes  so I decided to write the wrapper in python  but use the same basic  grab the version by running the exe  logic and came up with this    I think it should work for 2 5 and onwards  I ve tested it on 2 66  2 7 0 and 3 1 2 on Linux and 2 6 1 on OS X so far   import sys  subprocess args    sys executable  --version    output  error   subprocess Popen args  stdout   subprocess PIPE  stderr   subprocess PIPE  communicate   print  The version is    s     error decode sys stdout encoding  strip  qwertyuiopasdfghjklzxcvbnmQWERTYUIOPASDFGHJKLMNBVCXZ     n       Yes  I know the final decode strip line is horrible  but I just wanted to quickly grab the version number  I m going to refine that   This works well enough for me for now  but if anyone can improve it  or tell me why it s a terrible idea  that d be cool too

User · Answer

Sets became part of the core language in Python 2 4  in order to stay backwards compatible  I did this back then  which will work for you as well   if sys version info  lt   2  4       from sets import Set as set

User · Answer

I just found this question after a quick search whilst trying to solve the problem myself and I ve come up with a hybrid based on a few of the suggestions above   I like DevPlayer s idea of using a wrapper script  but the downside is that you end up maintaining multiple wrappers for different OSes  so I decided to write the wrapper in python  but use the same basic  grab the version by running the exe  logic and came up with this    I think it should work for 2 5 and onwards  I ve tested it on 2 66  2 7 0 and 3 1 2 on Linux and 2 6 1 on OS X so far   import sys  subprocess args    sys executable  --version    output  error   subprocess Popen args  stdout   subprocess PIPE  stderr   subprocess PIPE  communicate   print  The version is    s     error decode sys stdout encoding  strip  qwertyuiopasdfghjklzxcvbnmQWERTYUIOPASDFGHJKLMNBVCXZ     n       Yes  I know the final decode strip line is horrible  but I just wanted to quickly grab the version number  I m going to refine that   This works well enough for me for now  but if anyone can improve it  or tell me why it s a terrible idea  that d be cool too

User · Answer

import sys sys version   will be getting answer like this       2 7 6  default  Oct 26 2016  20 30 19   n GCC 4 8 4     here 2 7 6 is version

User · Answer

Put the following at the very top of your file   import sys  if float sys version split   0   3    lt  2 7      print  Python 2 7 or higher required to run this code      sys version split   0      detected  exiting       exit 1    Then continue on with the normal Python code   import     import     other code

User · Answer

For standalone python scripts  the following module docstring trick to enforce a python version  here v2 7 x  works  tested on  nix       bin sh     python -V 2 gt  amp 1   grep -q 2 7  amp  amp  exec python -u --   0    1        echo  python 2 7 x missing   exit 1        import sys         This should handle missing python executable as well but has a dependency on grep  See here for background

User · Answer

I think the best way is to test for functionality rather than versions  In some cases  this is trivial  not so in others   eg   try         Do stuff except     Features weren t found        Do stuff for older versions    As long as you re specific in enough in using the try except blocks  you can cover most of your bases

User · Answer

Sets became part of the core language in Python 2 4  in order to stay backwards compatible  I did this back then  which will work for you as well   if sys version info  lt   2  4       from sets import Set as set

User · Answer

Try    import platform platform python version     Should give you a string like  2 3 1   If this is not exactly waht you want there is a rich set of data available through the  platform  build-in  What you want should be in there somewhere

User · Answer

import sys       prints whether python is version 3 or not python version   sys version info major if python version    3      print  is python 3   else      print  not python 3

User · Answer

Have a wrapper around your program that does the following   import sys  req version    2 5  cur version   sys version info  if cur version  gt   req version     import myApp    myApp run   else     print  Your Python interpreter is too old  Please consider upgrading     You can also consider using sys version    if you plan to encounter people who are using pre-2 0 Python interpreters  but then you have some regular expressions to do   And there might be more elegant ways to do this

[python] How can I check for Python version in a program that uses new language features?

Examples related to python

Examples related to version