Python sys.executable is empty

Question

I am testing out doing some shenanigans with os.execve and virtual environments. I am running into the problem where sys.executable is empty if I replace the current python process with another python subprocess.

The example below shows what's going on (run this inside a python shell):

import os, sys
print(sys.executable) # works this time
os.execve("/usr/bin/python", [], {}) # drops me into a new python shell
import sys # yes, again
print(sys.executable) # is empty

The full output of me running the commands above in a python shell:

 lptp [ tmp ]: python
Python 2.7.10 (default, Oct 14 2015, 16:09:02) 
[GCC 5.2.1 20151010] on linux2
Type "help", "copyright", "credits" or "license" for more information.
>>> import os, sys
>>> print(sys.executable) # works this time
/usr/bin/python
>>> os.execve("/usr/bin/python", [], {}) # drops me into a new python shell
Python 2.7.10 (default, Oct 14 2015, 16:09:02) 
[GCC 5.2.1 20151010] on linux2
Type "help", "copyright", "credits" or "license" for more information.
>>> import sys # yes, again
>>> print(sys.executable) # is empty

>>>

sys.executable being empty is causing me problems, most notably that platform.libc_ver() fails because sys.executable is empty:

>>> import platform
>>> platform.libc_ver()
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/usr/lib/python2.7/platform.py", line 163, in libc_ver
    f = open(executable,'rb')
IOError: [Errno 21] Is a directory: '/tmp'

Note that the example above was run after calling os.execve(...)

Answer 1

Python relies on argv[0] and several environment variables to determine sys.executable. When you pass an empty argv and environment, Python doesn't know how to determine its path. At the very least, you should provide argv[0]:

os.execve('/usr/bin/python', ['/usr/bin/python'], {})