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.

One difference observed (Python27):

os.environ raises an exception if the environmental variable does not exist. os.getenv does not raise an exception, but returns None

How to Set and Get Environment Variables in Python, os.getenv() method in Python returns the value of the environment variable key if it import os. # Get the value of 'HOME'. # environment variable. key = 'HOME' Difference between Method Overloading and Method Overriding in Python  One answer I found very useful when learning about getting environment variables in Python code is knowing the difference between os.getenv and os.environ.get. Either one can be used in your applications but there are slight differences that can make one better than the other in various situations.

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.

Python, Is there any difference at all between these two? When should I use one over the other? Is one of these deprecated? They seem to have the  So we can conclude os.getenv is just a simple wrapper around os.environ.get. One difference observed (Python27): os.environ raises an exception if the environmental variable does not exist. os.getenv does not raise an exception, but returns None

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.

Difference between os.getenv and os.environ.get?, All functions in this module raise OSError in the case of invalid or Calling putenv() directly does not change os.environ , so it's better to modify os.environ . Note function, you can delete items in this mapping to unset environment variables. Fondamentalement, os.environ se trouve à l'importation, et os.getenv est une enveloppe à os.environ.get, au moins en CPython. EDIT: pour répondre à un commentaire, dans CPython, os.getenv est fondamentalement un raccourci à os.environ.get; depuis os.environ est chargé à l'importation de os, et seulement alors, la même chose vaut pour os

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.)

15.1. os — Miscellaneous operating system interfaces, Python Code : import os print("Access all environment variables:") print("​Access a particular environment variable:") print(os.environ['HOME'])  os.getlogin()can throw errors when run in certain situations. Using the LOGNAME, USER, USERNAME, etc. environment variables (after checking that they exist) is the safer option. If you're really worried about people changing the environment variables, then you can pull the username from the current process ID using pwd.getpwuid(os.getuid()).

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

Python: Access environment variables and value of the environment , This page provides Python code examples for os.getenv. Reinitialising the module contents # and just reverting os.environ to its previous state is an The only allowed format for environment variables defined in the requirement file is msg=import_out, rc=import_rc, cmd=import_cmd, stdout=import_out, diff=diff) else:  os.environ is documented as being a "mapping" object. The "get" method is a standard method for all mapping objects; it's not unique to os.environ. Thus, there is no need to specially call out "get" or any of the other "mapping" methods and operations available with os.environ or any other example of a mapping object.

os.getenv Python Example, os.name; os.environ; os.chdir(); os.getcwd(); os.getenv(); os.putenv(); os.mkdir() I find myself doing this a lot when I create a log file that is in a dated folder  os.getenv() method in Python returns the value of the environment variable key if it exists otherwise returns the default value. Syntax: os.getenv(key, default = None) Parameters: key: string denoting the name of environment variable default (optional) : string denoting the default value in case key does not exists.

Chapter 16, Returns a string that contains the value of the desired environment variable in the environment in which the ABL session is running. Syntax. OS-GETENV (  print os.getenv('MY_TEST_ENV') which always returns None . If I create a test-script to test this behavior, even with classes in different files, I always get the desired behavior, e.g., os.getenv('MY_TEST_ENV') returns the correct value 4711 .

OS-GETENV function - Documentation, answer I found very useful when learning about getting environment variables in Python code is knowing the difference between os.getenv and os.environ.get. Parameter: It is a non-callable object. Hence, no parameter is required . Return Type: This returns a dictionary representing the user’s environmental variables Code #1: Use of os.environ to get access of environment variables

Comments
  • The OP asks about os.environ.get() which returns None (unless specified differently) and never raises an exception if the env. var. doesn't exists. Your confusing things with using os.environ['TERM'] which is not what the question is about.
  • The OP's question asks about os.environ.get() vs os.getenv() but the body also includes os.environ vs. os.environ.get() so this answer correct in at least some ways - incomplete, but correct.
  • This incorrect and misleading answer should have received negative down votes. The next answer is the right one.
  • Indeed, it is, according to the official doc: docs.python.org/3/library/os.html
  • From the linked related thread: "the main reason to use os.getenv() [...] is when you want to have a default value returned when an environment variable name isn't found in os.environ's keys rather than have a KeyError or whatever thrown, and you want to save a few characters."
  • Which version of Python have you tested with. On 3.7.2, os.getenv is just a wrapper for os.environ.get, so I am getting very minimal overhead.
  • That was 3.7.1 on macOS Mojave. Timings were pretty consistent.
  • @PreslavRachev minimal or not it is an extra function call, so there is some overhead. That being said, you probably don't need to retrieve env variables in the middle of your inner loop.
  • Totally irrelevant. Micro-optimization of a single function call... Any application should read the environment only on bootstrap anyways, making this even more irrelevant.
  • BTW, usec is a microsecond in timeit. The difference found in this micro-benchmarking was 0.18 microseconds...