如何在 Python 中访问环境变量？

Question

如何在 Python 中获取环境变量的值？

Answer 1

Environment variables are accessed through os.environ :

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

To see a list of all environment variables:

print(os.environ)

---

If a key is not present, attempting to access it will raise a KeyError . To avoid this:

# Returns `None` if key doesn't exist
print(os.environ.get('KEY_THAT_MIGHT_EXIST'))

# Returns `default_value` if key doesn't exist
print(os.environ.get('KEY_THAT_MIGHT_EXIST', default_value))

# Returns `default_value` if key doesn't exist
print(os.getenv('KEY_THAT_MIGHT_EXIST', default_value))

Answer 2

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

Answer 3

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)

Answer 4

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'

Answer 5

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.

Answer 6

As for the environment variables:

import os
print os.environ["HOME"]

Answer 7

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.

Answer 8

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'

Answer 9

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).

Answer 10

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']

Answer 11

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 .

Answer 12

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"])

PS- if you worry about exposing private environment variables, then sanitize env_dict after the assignment.

Answer 13

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')

Answer 14

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.

Answer 15

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))"

Answer 16

.env File

Here is my .env file (I changed multiple characters in each key to prevent people hacking my accounts).

SECRET_KEY=6g18169690e33af0cb10f3eb6b3cb36cb448b7d31f751cde
AWS_SECRET_ACCESS_KEY=18df6c6e95ab3832c5d09486779dcb1466ebbb12b141a0c4
DATABASE_URL='postgres://drjpczkqhnuvkc:f0ba6afd133c53913a4df103187b2a34c14234e7ae4b644952534c4dba74352d@ec2-54-146-4-66.compute-1.amazonaws.com:5432/ddnl5mnb76cne4'
AWS_ACCESS_KEY_ID=AKIBUGFPPLQFTFVDVIFE
DISABLE_COLLECTSTATIC=1
EMAIL_HOST_PASSWORD=COMING SOON
MAILCHIMP_API_KEY=a9782cc1adcd8160907ab76064411efe-us17
MAILCHIMP_EMAIL_LIST_ID=5a6a2c63b7
STRIPE_PUB_KEY=pk_test_51HEF86ARPAz7urwyGw9xwLkgbgfCYT48LttlwjEkb88I7Ljb5soBtuKXBaPiKfuu0Cx2BzIowR3jJFkC8ybFBAEf00DFY46tB8
STRIPE_SECRET_KEY=sk_test_19HEF55BCEAz7urwytx7tO3QCxV4R8DEFXbqj6esg7OKuybiSTI8iJD8mmJUQpg4RKENxuS04DKOCzYHpDkAjUttO00LOmsT5Eg

settings

I was told my data was corrupted. I was struggling to work out what was going on. I had a suspicion the values from .env were not being passed into my settings file.

print(os.environ.get('AWS_SECRET_ACCESS_KEY'))
print(os.environ.get('AWS_ACCESS_KEY_ID'))
print(os.environ.get('AWS_SECRET_ACCESS_KEY'))
print(os.environ.get('DATABASE_URL'))
print(os.environ.get('SECRET_KEY'))
print(os.environ.get('DISABLE_COLLECTSTATIC'))
print(os.environ.get('EMAIL_HOST_PASSWORD'))
print(os.environ.get('MAILCHIMP_API_KEY'))
print(os.environ.get('MAILCHIMP_EMAIL_LIST_ID'))
print(os.environ.get('STRIPE_PUB_KEY'))
print(os.environ.get('STRIPE_SECRET_KEY'))

The only value being printed correctly was the SECRET_KEY. I reviewed the .env file and for the life of me could not see any reason why the SECRET_KEY was working and nothing else.

I got everything working eventually by putting this above the print statements.

from dotenv import load_dotenv   #for python-dotenv method
load_dotenv()                    #for python-dotenv method

And doing

pip install -U python-dotenv

I am still not sure why SECRET_KEY was working when all the others were broken.