How to read Windows environment variable value?

Question

I tried this:

os.environ['MyVar'] 

But it did not work! Is there any way suitable for all operating systems?

Answer 1

Try using the following:

os.getenv('MyVar') 

From the documentation:

os.getenv(varname[, value])

Return the value of the environment variable varname if it exists, or value if it doesn’t. value defaults to None.

Availability: most flavors of Unix, Windows

So after testing it:

>>> import os >>> os.environ['MyVar'] = 'Hello World!'       # set the environment variable 'MyVar' to contain 'Hello World!' >>> print os.getenv('MyVar') Hello World! >>> print os.getenv('not_existing_variable') None >>> print os.getenv('not_existing_variable', 'that variable does not exist') that variable does not exist >>> print os.environ['MyVar'] Hello World! >>> print os.environ['not_existing_variable'] Traceback (most recent call last):   File "<stdin>", line 1, in ?   File "/usr/lib/python2.4/UserDict.py", line 17, in __getitem__     def __getitem__(self, key): return self.data[key] KeyError: 'not_existing_variable     

Your method would work too if the environmental variable exists. The difference with using os.getenv is that it returns None (or the given value), while os.environ['MyValue'] gives a KeyError exception when the variable does not exist.