CODEWITHSUNDEEP
pythonenvironment-variablespython-os
André Staltz
André Staltz

Reputation: 13974

Difference between os.getenv and os.environ.get

Is there any difference at all between both approaches?

>>> os.getenv('TERM')
'xterm'
>>> os.environ.get('TERM')
'xterm'

>>> os.getenv('FOOBAR', "not found") == "not found"
True
>>> os.environ.get('FOOBAR', "not found") == "not found"
True

They seem to have the exact same functionality.

Upvotes: 409

Views: 323449

Answers (5)

fredrik
fredrik

Reputation: 10281

In addition to the answers above:

$ python3 -m timeit -s 'import os' 'os.environ.get("TERM_PROGRAM")'
200000 loops, best of 5: 1.65 usec per loop

$ python3 -m timeit -s 'import os' 'os.getenv("TERM_PROGRAM")'
200000 loops, best of 5: 1.83 usec per loop

EDIT: meaning, no difference

Upvotes: 14

giwyni
giwyni

Reputation: 3346

One difference (observed in Python 2.7 and 3.8) between getenv() and environ[]:

  • os.getenv() does not raise an exception, but returns None
  • os.environ.get() similarly returns None
  • os.environ[] raises an exception if the environmental variable does not exist

Upvotes: 202

user2357112
user2357112

Reputation: 280182

While there is no functional difference between os.environ.get and os.getenv, there is a massive difference between os.putenv and setting entries on os.environ. os.putenv is broken, so you should default to os.environ.get simply to avoid the way os.getenv encourages you to use os.putenv for symmetry.

os.putenv changes the actual OS-level environment variables, but in a way that doesn't show up through os.getenv, os.environ, or any other stdlib way of inspecting environment variables:

>>> import os
>>> os.environ['asdf'] = 'fdsa'
>>> os.environ['asdf']
'fdsa'
>>> os.putenv('aaaa', 'bbbb')
>>> os.getenv('aaaa')
>>> os.environ.get('aaaa')

You'd probably have to make a ctypes call to the C-level getenv to see the real environment variables after calling os.putenv. (Launching a shell subprocess and asking it for its environment variables might work too, if you're very careful about escaping and --norc/--noprofile/anything else you need to do to avoid startup configuration, but it seems a lot harder to get right.)

Upvotes: 75

Zulu
Zulu

Reputation: 9265

In Python 2.7 with iPython:

>>> import os
>>> os.getenv??
Signature: os.getenv(key, default=None)
Source:
def getenv(key, default=None):
    """Get an environment variable, return None if it doesn't exist.
    The optional second argument can specify an alternate default."""
    return environ.get(key, default)
File:      ~/venv/lib/python2.7/os.py
Type:      function

So we can conclude os.getenv is just a simple wrapper around os.environ.get.

Upvotes: 56

W. Conrad Walden
W. Conrad Walden

Reputation: 2562

See this related thread. Basically, os.environ is found on import, and os.getenv is a wrapper to os.environ.get, at least in CPython.

EDIT: To respond to a comment, in CPython, os.getenv is basically a shortcut to os.environ.get ; since os.environ is loaded at import of os, and only then, the same holds for os.getenv.

Upvotes: 236

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