Is module file attribute absolute or relative

Question

I m having trouble understanding   file    From what I understand    file   returns the absolute path from which the module was loaded    I m having problem producing this  I have a abc py with one statement print   file    running from  d projects  python abc py returns abc py  running from  d  returns projects abc py  Any reasons why

User · Answer

Late simple example   from os import path  getcwd  chdir  def print my path        print  cwd          format getcwd         print    file       format   file         print  abspath      format path abspath   file       print my path    chdir        print my path     Under Python-2    the second call incorrectly determines the path abspath   file    based on the current directory   cwd      C  codes py   file   cwd mayhem py abspath  C  codes py cwd mayhem py cwd      C  codes   file   cwd mayhem py abspath  C  codes cwd mayhem py   As noted by  techtonik  in Python 3 4   this will work fine since   file   returns an absolute path

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From the documentation        file   is the pathname of the file from which the module was loaded  if it was loaded from a file  The   file   attribute is not present for C modules that are statically linked into the interpreter  for extension modules loaded dynamically from a shared library  it is the pathname of the shared library file    From the mailing list thread linked by  kindall in a comment to the question      I haven t tried to repro this particular example  but the reason is   that we don t want to have to call getpwd   on every import nor do we   want to have some kind of in-process variable to cache the current   directory   getpwd   is relatively slow and can sometimes fail   outright  and trying to cache it has a certain risk of being wrong        What we do instead  is code in site py that walks over the elements of   sys path and turns them into absolute paths  However this code runs   before    is inserted in the front of sys path  so that the initial   value of sys path is       For the rest of this  consider sys path not to include      So  if you are outside the part of sys path that contains the module  you ll get an absolute path  If you are inside the part of sys path that contains the module  you ll get a relative path   If you load a module in the current directory  and the current directory isn t in sys path  you ll get an absolute path   If you load a module in the current directory  and the current directory is in sys path  you ll get a relative path

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With the help of the of Guido mail provided by  kindall  we can understand the standard import process as trying to find the module in each member of sys path  and file as the result of this lookup  more details in PyMOTW Modules and Imports    So if the module is located in an absolute path in sys path the result is absolute  but if it is located in a relative path in sys path the result is relative   Now the site py startup file takes care of delivering only absolute path in sys path  except the initial     so if you don t change it by other means than setting the PYTHONPATH  whose path are also made absolute  before prefixing sys path   you will get always an absolute path  but when the module is accessed through the current directory   Now if you trick sys path in a funny way you can get anything   As example if you have a sample module foo py in  tmp  with the code   import sys print sys path  print    file      If you go in  tmp you get    gt  gt  gt  import foo        tmp     usr lib python3 3          foo py   When in  in  home user  if you add  tmp your PYTHONPATH you get    gt  gt  gt  import foo        tmp     usr lib python3 3         tmp foo py   Even if you add       tmp  it will be normalized and the result is the same   But if instead of using PYTHONPATH you use directly some funny path you get a result as funny as the cause    gt  gt  gt  import sys  gt  gt  gt  sys path append        tmp    gt  gt  gt  import foo        usr lib python3 3                 tmp         tmp foo py   Guido explains in the above cited thread  why python do not try to transform all entries in absolute paths      we don t want to have to call getpwd   on every import        getpwd   is relatively slow and can sometimes fail outright    So your path is used as it is

User · Answer

file   is absolute since Python 3 4  except when executing a script directly using a relative path      Module   file   attributes  and related values  should now always contain absolute paths by default  with the sole exception of   main     file   when a script has been executed directly using a relative path   Contributed by Brett Cannon in bpo-18416     Not sure if it resolves symlinks though   Example of passing a relative path     python script py

[python] Is module file attribute absolute or relative?

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