Reading environment variables in python

The os module contains an interface to operating system-specific functions. this module can be used to access environment variables. 

We can go with os.environ to get the value of environment variable.

import os
print os.environ['HOME']

but there is a catch, this method will raise KeyError variable does not exist 

>>> print os.environ['HOME_NOT_EXIST']
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/usr/lib/python2.7/UserDict.py", line 23, in __getitem__
    raise KeyError(key)
KeyError: 'HOME_NOT_EXIST'




So it is better to go with os.getenv. this return None if key/environment variable does not exist. and if we require we can return default values too.




print os.getenv('KEY')    #returns None if KEY doesn't exist

print os.getenv('KEY', 0) #will return 0 if KEY doesn't exist