How do I access environment variables in Python?
PythonEnvironment VariablesPython Problem Overview
How do I get the value of an environment variable in Python?
Python Solutions
Solution 1 - Python
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:
os.environ
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)
Solution 2 - Python
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
Solution 3 - Python
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)
Solution 4 - Python
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:
print(os.environ['HOME'])
Or:
print(os.environ.get('HOME'))
To set the value:
os.environ['HOME'] = '/new/value'
Solution 5 - Python
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.
Solution 6 - Python
As for the environment variables:
import os
print os.environ["HOME"]
Solution 7 - Python
import os
for a in os.environ:
print('Var: ', a, 'Value: ', os.getenv(a))
print("all done")
That will print all of the environment variables along with their values.
Solution 8 - Python
Import the os
module:
import os
To get an environment variable:
os.environ.get('Env_var')
To set an environment variable:
# Set environment variables
os.environ['Env_var'] = 'Some Value'
Solution 9 - Python
If you are planning to use the code in a production web application code, using any web framework like Django and Flask, use projects like envparse. Using it, you can read the value as your defined type.
from envparse import env
# will read WHITE_LIST=hello,world,hi to white_list = ["hello", "world", "hi"]
white_list = env.list("WHITE_LIST", default=[])
# Perfect for reading boolean
DEBUG = env.bool("DEBUG", default=False)
NOTE: kennethreitz's autoenv is a recommended tool for making project-specific environment variables. For those who are using autoenv
, please note to keep the .env
file private (inaccessible to public).
Solution 10 - Python
There are also a number of great libraries. Envs, for example, will allow you to parse objects out of your environment variables, which is rad. For example:
from envs import env
env('SECRET_KEY') # 'your_secret_key_here'
env('SERVER_NAMES',var_type='list') #['your', 'list', 'here']
Solution 11 - Python
You can also try this:
First, install python-decouple
pip install python-decouple
Import it in your file
from decouple import config
Then get the environment variable
SECRET_KEY=config('SECRET_KEY')
Read more about the Python library here.
Solution 12 - Python
Edited - October 2021
Following @Peter's comment, here's how you can test it:
main.py
#!/usr/bin/env python
from os import environ
# Initialize variables
num_of_vars = 50
for i in range(1, num_of_vars):
environ[f"_BENCHMARK_{i}"] = f"BENCHMARK VALUE {i}"
def stopwatch(repeat=1, autorun=True):
"""
Source: https://stackoverflow.com/a/68660080/5285732
stopwatch decorator to calculate the total time of a function
"""
import timeit
import functools
def outer_func(func):
@functools.wraps(func)
def time_func(*args, **kwargs):
t1 = timeit.default_timer()
for _ in range(repeat):
r = func(*args, **kwargs)
t2 = timeit.default_timer()
print(f"Function={func.__name__}, Time={t2 - t1}")
return r
if autorun:
try:
time_func()
except TypeError:
raise Exception(f"{time_func.__name__}: autorun only works with no parameters, you may want to use @stopwatch(autorun=False)") from None
return time_func
if callable(repeat):
func = repeat
repeat = 1
return outer_func(func)
return outer_func
@stopwatch(repeat=10000)
def using_environ():
for item in environ:
pass
@stopwatch
def using_dict(repeat=10000):
env_vars_dict = dict(environ)
for item in env_vars_dict:
pass
python "main.py"
# Output
Function=using_environ, Time=0.216224731
Function=using_dict, Time=0.00014206099999999888
If this is true ... It's 1500x faster to use a dict()
instead of accessing environ
directly.
A performance-driven approach - calling environ
is expensive, so it's better to call it once and save it to a dictionary. Full example:
from os import environ
# Slower
print(environ["USER"], environ["NAME"])
# Faster
env_dict = dict(environ)
print(env_dict["USER"], env_dict["NAME"])
P.S- if you worry about exposing private environment variables, then sanitize env_dict
after the assignment.
Solution 13 - Python
For Django, see Django-environ.
$ pip install django-environ
import environ
env = environ.Env(
# set casting, default value
DEBUG=(bool, False)
)
# reading .env file
environ.Env.read_env()
# False if not in os.environ
DEBUG = env('DEBUG')
# Raises Django's ImproperlyConfigured exception if SECRET_KEY not in os.environ
SECRET_KEY = env('SECRET_KEY')
Solution 14 - Python
You should first import os using
import os
and then actually print the environment variable value
print(os.environ['yourvariable'])
of course, replace yourvariable as the variable you want to access.
Solution 15 - Python
The tricky part of using nested for-loops in one-liners is that you have to use list comprehension. So in order to print all your environment variables, without having to import a foreign library, you can use:
python -c "import os;L=[f'{k}={v}' for k,v in os.environ.items()]; print('\n'.join(L))"