python - How to access environment variable values

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Top 5 Answer for python - How to access environment variable values

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Environment variables are accessed through os.environ

import os print(os.environ['HOME']) 

Or you can see a list of all the environment variables using:


As sometimes you might need to see a complete list!

# using get will return `None` if a key is not present rather than raise a `KeyError` print(os.environ.get('KEY_THAT_MIGHT_EXIST'))  # os.getenv is equivalent, and can also give a default value instead of `None` print(os.getenv('KEY_THAT_MIGHT_EXIST', default_value)) 

The Python default installation location on Windows is C:\Python. If you want to find out while running python you can do:

import sys print(sys.prefix) 
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To check if the key exists (returns True or False)

'HOME' in os.environ 

You can also use get() when printing the key; useful if you want to use a default.

print(os.environ.get('HOME', '/home/username/')) 

where /home/username/ is the default

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The original question (first part) was "how to check environment variables in Python."

Here's how to check if $FOO is set:

try:      os.environ["FOO"] except KeyError:     print "Please set the environment variable FOO"    sys.exit(1) 
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Actually it can be done this way:

import os  for item, value in os.environ.items():     print('{}: {}'.format(item, value)) 

Or simply:

for i, j in os.environ.items():     print(i, j) 

For viewing the value in the parameter:




To set the value:

os.environ['HOME'] = '/new/value' 
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You can access the environment variables using

import os print os.environ 

Try to see the content of the PYTHONPATH or PYTHONHOME environment variables. Maybe this will be helpful for your second question.

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