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Environment Variables in Python – Read, Print, Set

Environment variables is the set of key-value pairs for the current user environment. They are generally set by the operating system and the current user-specific configurations. For example, in a Unix environment, the environment variables are set using the user profile i.e. .bash_profile, .bashrc, or .profile files.


Environment Variables in Python

You can think of environment variables as a dictionary, where the key is the environment variable name and the value is the environment variable value.


How to Read Environment Variables in Python

We can use Python os module “environ” property to get the dictionary of all the environment variables. When the os module is loaded by Python interpreter, the environ value is set. Any further changes in the environment variables through external programs will not get reflected in the already running Python program.


Printing all the Environment Variables in Python

The os.environ variable is a dictionary-like object. If we print it, all the environment variables name and values will get printed.

import os

# printing environment variables
print(os.environ)

Output:

environ({'PATH': '/Users/pankaj/Documents/PyCharmProjects/PythonTutorialPro/venv/bin:/Library/Java/JavaVirtualMachines/jdk-12.jdk/Contents/Home/bin:/Library/PostgreSQL/10/bin:/Users/pankaj/Downloads/mongodb/bin:/Library/Frameworks/Python.framework/Versions/3.7/bin:/Users/pankaj/Downloads/apache-maven-3.5.3/bin:/Library/Frameworks/Python.framework/Versions/3.7/bin:/usr/local/bin:/usr/bin:/bin:/usr/sbin:/sbin', 'PS1': '(venv) ', 'MAVEN_OPTS': '-Xmx2048m -XX:MaxPermSize=128m', 'VERSIONER_PYTHON_VERSION': '2.7', 'LOGNAME': 'pankaj', 'XPC_SERVICE_NAME': 'com.jetbrains.pycharm.40096', 'PWD': '/Users/pankaj/Documents/PycharmProjects/AskPython/hello-world', 'PYCHARM_HOSTED': '1', 'PYTHONPATH': '/Users/pankaj/Documents/PycharmProjects/AskPython', 'SHELL': '/bin/zsh', 'PAGER': 'less', 'LSCOLORS': 'Gxfxcxdxbxegedabagacad', 'PYTHONIOENCODING': 'UTF-8', 'OLDPWD': '/Applications/PyCharm CE.app/Contents/bin', 'VERSIONER_PYTHON_PREFER_32_BIT': 'no', 'USER': 'pankaj', 'ZSH': '/Users/pankaj/.oh-my-zsh', 'TMPDIR': '/var/folders/1t/sx2jbcl534z88byy78_36ykr0000gn/T/', 'SSH_AUTH_SOCK': '/private/tmp/com.apple.launchd.jkodHSyv2v/Listeners', 'VIRTUAL_ENV': '/Users/pankaj/Documents/PyCharmProjects/PythonTutorialPro/venv', 'XPC_FLAGS': '0x0', 'PYTHONUNBUFFERED': '1', 'M2_HOME': '/Users/pankaj/Downloads/apache-maven-3.5.3', '__CF_USER_TEXT_ENCODING': '0x1F5:0x0:0x0', 'Apple_PubSub_Socket_Render': '/private/tmp/com.apple.launchd.wL2naXrbuW/Render', 'LESS': '-R', 'LC_CTYPE': 'UTF-8', 'HOME': '/Users/pankaj', '__PYVENV_LAUNCHER__': '/Users/pankaj/Documents/PycharmProjects/AskPython/venv/bin/python'})
Environment Variable In Python
Environment Variable in Python

If you want to print the environment variables in a better readable way, you can print them in a for loop.

import os

for k, v in os.environ.items():
    print(f'{k}={v}')

Output:

PATH=/Users/pankaj/Documents/PyCharmProjects/PythonTutorialPro/venv/bin:/Library/Java/JavaVirtualMachines/jdk-12.jdk/Contents/Home/bin:/Library/PostgreSQL/10/bin:/Users/pankaj/Downloads/mongodb/bin:/Library/Frameworks/Python.framework/Versions/3.7/bin:/Users/pankaj/Downloads/apache-maven-3.5.3/bin:/Library/Frameworks/Python.framework/Versions/3.7/bin:/usr/local/bin:/usr/bin:/bin:/usr/sbin:/sbin
PS1=(venv) 
MAVEN_OPTS=-Xmx2048m -XX:MaxPermSize=128m
VERSIONER_PYTHON_VERSION=2.7
LOGNAME=pankaj
XPC_SERVICE_NAME=com.jetbrains.pycharm.40096
PWD=/Users/pankaj/Documents/PycharmProjects/AskPython/hello-world
PYCHARM_HOSTED=1
PYTHONPATH=/Users/pankaj/Documents/PycharmProjects/AskPython
SHELL=/bin/zsh
PAGER=less
LSCOLORS=Gxfxcxdxbxegedabagacad
PYTHONIOENCODING=UTF-8
OLDPWD=/Applications/PyCharm CE.app/Contents/bin
VERSIONER_PYTHON_PREFER_32_BIT=no
USER=pankaj
ZSH=/Users/pankaj/.oh-my-zsh
TMPDIR=/var/folders/1t/sx2jbcl534z88byy78_36ykr0000gn/T/
SSH_AUTH_SOCK=/private/tmp/com.apple.launchd.jkodHSyv2v/Listeners
VIRTUAL_ENV=/Users/pankaj/Documents/PyCharmProjects/PythonTutorialPro/venv
XPC_FLAGS=0x0
PYTHONUNBUFFERED=1
M2_HOME=/Users/pankaj/Downloads/apache-maven-3.5.3
__CF_USER_TEXT_ENCODING=0x1F5:0x0:0x0
Apple_PubSub_Socket_Render=/private/tmp/com.apple.launchd.wL2naXrbuW/Render
LESS=-R
LC_CTYPE=UTF-8

Getting Specific Environment Variable Value

Since os.environ is a dictionary object, we can get the specific environment variable value using the key.

import os

home_dir =os.environ['HOME']
username = os.environ['USER']
print(f'{username} home directory is {home_dir}')

Output: pankaj home directory is /Users/pankaj

However, this way to get the environment variable will raise KeyError if the environment variable is not present.

>>> import os
>>> env_var = input('Please enter the environment variable name:\n')
Please enter the environment variable name:
data
>>> print(os.environ[env_var])
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/Library/Frameworks/Python.framework/Versions/3.7/lib/python3.7/os.py", line 678, in __getitem__
    raise KeyError(key) from None
KeyError: 'data'
>>>

A better way to get the environment variable is to use the dictionary get() function. We can also specify the default value if the environment variable is not present.

>>> import os
>>> env_var = input('Please enter the environment variable name:\n')
Please enter the environment variable name:
data
>>> print(os.environ.get(env_var))
None
>>> print(os.environ.get(env_var, 'CSV'))
CSV

How to Check if an Environment Variable Exists?

We can use the “in” operator to check if an environment variable exists or not.

import os

env_var = input('Please enter the environment variable name:\n')

if env_var in os.environ:
    print(f'{env_var} value is {os.environ[env_var]}')
else:
    print(f'{env_var} does not exist')

Output:

# Run 1
Please enter the environment variable name:
datatype
datatype does not exist

# Run 2
Please enter the environment variable name:
USER
USER value is pankaj

How to Set Environment Variable in Python

We can set the environment variable value using the syntax: os.environ[env_var] = env_var_value

import os

env_var = input('Please enter environment variable name:\n')

env_var_value = input('Please enter environment variable value:\n')

os.environ[env_var] = env_var_value

print(f'{env_var}={os.environ[env_var]} environment variable has been set.')

Output:

Please enter environment variable name:
datatype
Please enter environment variable value:
CSV
datatype=CSV environment variable has been set.

If the environment variable already exists, it will be overwritten by the new value. The environment variable will be set only for the current session of the Python interpreter. If you want to change to be permanent, then you will have to edit the user profile file in the Python program.


Conclusion

It’s very easy to work with environment variables in Python. We can read, add, and update environment variables for the current execution.


References: