Python os path join on Windows

Question

I am trying to learn python and am making a program that will output a script   I want to use os path join  but am pretty confused   According to the docs if I say   os path join  c     sourcedir     I get  C sourcedir    According to the docs  this is normal  right   But when I use the copytree command  Python will output it the desired way  for example   import shutil src   os path join  c     src   dst   os path join  c     dst   shutil copytree src  dst    Here is the error code I get    WindowsError   Error 3  The system cannot find the path specified   C src        If I wrap the os path join with os path normpath I get the same error   If this os path join can t be used this way  then I am confused as to its purpose   According to the pages suggested by Stack Overflow  slashes should not be used in join mdash that is correct  I assume

User · Answer

I d say this is a  windows python bug   Why bug    I think this statement should be True  os path join  os path dirname os path abspath   file     split os path sep    os path dirname os path abspath   file       But it is False on windows machines

User · Answer

For a system-agnostic solution that works on both Windows and Linux  no matter what the input path  one could use os path join os sep  rootdir   os sep  targetdir    On WIndows    gt  gt  gt  os path join os sep   C     os sep   Windows    C   Windows    On Linux    gt  gt  gt  os path join os sep   usr    os sep   lib     usr lib

User · Answer

You have a few possible approaches to treat path on Windows  from the most hardcoded ones  as using raw string literals or escaping backslashes  to the least ones  Here follows a few examples that will work as expected  Use what better fits your needs   In 1   from os path import join  isdir  In 2   from os import sep  In 3   isdir join  c           Users    Out 3   True  In 4   isdir join  c          Users    Out 4   True  In 5   isdir join  c    sep   Users    Out 5   True

User · Answer

To be pedantic  it s probably not good to hardcode either   or   as the path separator   Maybe this would be best   mypath   os path join  c  s    os sep   sourcedir     or   mypath   os path join  c     os sep   sourcedir

User · Answer

Windows has a concept of current directory for each drive   Because of that   c sourcedir  means  sourcedir  inside the current C  directory  and you ll need to specify an absolute directory   Any of these should work and give the same result  but I don t have a Windows VM fired up at the moment to double check    c  sourcedir  os path join       c     sourcedir   os path join  c      sourcedir

User · Answer

The proposed solutions are interesting and offer a good reference  however they are only partially satisfying  It is ok to manually add the separator when you have a single specific case or you know the format of the input string  but there can be cases where you want to do it programmatically on generic inputs   With a bit of experimenting  I believe the criteria is that the path delimiter is not added if the first segment is a drive letter  meaning a single letter followed by a colon  no matter if it corresponds to a real unit   For example   import os testval     c    c      d    j    jr    data     for t in testval      print   test value    t    join to  folder   os path join t  folder       test value   c    join to  folder  c folder test value   c     join to  folder  c  folder test value   d    join to  folder  d folder test value   j    join to  folder  j folder test value   jr    join to  folder  jr  folder test value   data    join to  folder  data  folder    A convenient way to test for the criteria and apply a path correction can be to use os path splitdrive comparing the first returned element to the test value  like t os path sep if os path splitdrive t  0   t else t   Test   for t in testval      corrected   t os path sep if os path splitdrive t  0   t else t     print   original   s tcorrected   s   t corrected    join corrected- gt   os path join corrected  folder       original  c     corrected  c    join corrected- gt  c  folder original  c     corrected  c    join corrected- gt  c  folder original  d     corrected  d    join corrected- gt  d  folder original  j     corrected  j    join corrected- gt  j  folder original  jr    corrected  jr   join corrected- gt  jr  folder original  data  corrected  data   join corrected- gt  data  folder    it can be probably be improved to be more robust for trailing spaces  and I have tested it only on windows  but I hope it gives an idea  See also Os path   can you explain this behavior  for interesting details on systems other then windows

User · Answer

Consent with  georg-  I would say then why we need lame os path join- better to use str join or unicode join e g   sys path append   0   join os path dirname   file    split os path sep  0 -1   format os path sep

User · Answer

answering to your comment    the others        c     c     did not work  C    created two backslashes  C   didn t work at all    On windows using  os path join  c     sourcedir   will automatically add two backslashes    in front of sourcedir   To resolve the path  as python works on windows also with forward slashes -       simply add  replace           with os path join as below -  os path join  c       sourcedir   replace            e g  os path join  c       temp   replace            output    C  temp

User · Answer

To be even more pedantic  the most python doc consistent answer would be   mypath   os path join  c    os sep   sourcedir     Since you also need os sep for the posix root path   mypath   os path join os sep   usr    lib

User · Answer

The reason os path join  C     src   is not working as you expect is because of something in the documentation that you linked to      Note that on Windows  since there is a   current directory for each drive    os path join  c     foo   represents a   path relative to the current directory   on drive C   c foo   not c  foo    As ghostdog said  you probably want mypath os path join  c       sourcedir

User · Answer

to join a windows path  try  mypath os path join  c       sourcedir     basically  you will need to escape the slash

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