pywin32.pth: don't blindly append to PATH in case site is repeatedly reload()ed

[ksmyth]

pywin32.pth appends to the PATH environment variable. When the site module is reload()ed, it re-evaluates .pth files. When an environment variable gets too long (~32k), CreateProcess fails.

This PR modifies pywin32.pth to append to PATH only if the entry is not already present.

POC:

import os
import subprocess
import site


for i in range(1000):
    old_path = os.environ['PATH']
    reload(site)
    if len(old_path) >= len(os.environ['PATH']):
        break
print i

subprocess.check_call('cmd /c set')

Output:

c:\Python27\python test.py
Error processing line 11 of c:\Python27\lib\site-packages\pywin32.pth:

  Traceback (most recent call last):
    File "c:\Python27\lib\site.py", line 152, in addpackage
      exec line
    File "<string>", line 1, in <module>
    File "c:\Python27\lib\os.py", line 422, in __setitem__
      putenv(key, item)
  ValueError: the environment variable is longer than 32767 bytes

Remainder of file ignored
660
Traceback (most recent call last):
  File "test.py", line 13, in <module>
    subprocess.check_call('cmd /c set')
  File "c:\Python27\lib\subprocess.py", line 181, in check_call
    retcode = call(*popenargs, **kwargs)
  File "c:\Python27\lib\subprocess.py", line 168, in call
    return Popen(*popenargs, **kwargs).wait()
  File "c:\Python27\lib\subprocess.py", line 390, in __init__
    errread, errwrite)
  File "c:\Python27\lib\subprocess.py", line 640, in _execute_child
    startupinfo)
WindowsError: [Error 8] Not enough memory resources are available to process this command

[thopiekar]

Love it. Never observed this, but your output definitely proofs that it might happen.
I'm sure that @mhammond will merge this as soon has he finds the time to review it 😉👍

[mhammond]

Thanks!