如何在 Python 中获取环境变量的值?
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))
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
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)
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'
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.
As for the environment variables:
import os
print os.environ["HOME"]
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.
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'
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).
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']
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 .
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.
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')
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.
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))"
.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.
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