How to set environment variables in Python?

Question

I need to set some environment variables in the Python script and I want all the other scripts that are called from Python to see the environment variables\' set.

If

Answer 1

I have been trying to add environment variables. My goal was to store some user information to system variables such that I can use those variables for future solutions, as an alternative to config files. However, the method described in the code below did not help me at all.

import os
os.environ["variable_1"] = "value_1"
os.environ["variable_2"] = "value_2"
# To Verify above code
os.environ.get("variable_1")
os.environ.get("variable_2")

This simple code block works well, however, these variables exist inside the respective processes such that you will not find them in the environment variables tab of windows system settings. Pretty much above code did not serve my purpose. This problem is discussed here: variable save problem

os.environ.putenv(key, value)

Another unsuccessful attempt. So, finally, I managed to save variable successfully inside the window environment register by mimicking the windows shell commands wrapped inside the system class of os package. The following code describes this successful attempt.

os.system("SETX {0} {1} /M".format(key, value))

I hope this will be helpful for some of you.

Answer 2

You may need to consider some further aspects for code robustness;

when you're storing an integer-valued variable as an environment variable, try

os.environ['DEBUSSY'] = str(myintvariable)

then for retrieval, consider that to avoid errors, you should try

os.environ.get('DEBUSSY', 'Not Set')

possibly substitute '-1' for 'Not Set'

so, to put that all together

myintvariable = 1
os.environ['DEBUSSY'] = str(myintvariable)
strauss = int(os.environ.get('STRAUSS', '-1'))
# NB KeyError <=> strauss = os.environ['STRAUSS']
debussy = int(os.environ.get('DEBUSSY', '-1'))

print "%s %u, %s %u" % ('Strauss', strauss, 'Debussy', debussy)

Answer 3

You can use the os.environ dictionary to access your environment variables.

Now, a problem I had is that if I tried to use os.system to run a batch file that sets your environment variables (using the SET command in a **.bat* file) it would not really set them for your python environment (but for the child process that is created with the os.system function). To actually get the variables set in the python environment, I use this script:

import re
import system
import os

def setEnvBat(batFilePath, verbose = False):
    SetEnvPattern = re.compile("set (\w+)(?:=)(.*)$", re.MULTILINE)
    SetEnvFile = open(batFilePath, "r")
    SetEnvText = SetEnvFile.read()
    SetEnvMatchList = re.findall(SetEnvPattern, SetEnvText)

    for SetEnvMatch in SetEnvMatchList:
        VarName=SetEnvMatch[0]
        VarValue=SetEnvMatch[1]
        if verbose:
            print "%s=%s"%(VarName,VarValue)
        os.environ[VarName]=VarValue

Answer 4

It should be noted that if you try to set the environment variable to a bash evaluation it won't store what you expect. Example:

from os import environ

environ["JAVA_HOME"] = "$(/usr/libexec/java_home)"

This won't evaluate it like it does in a shell, so instead of getting /Library/Java/JavaVirtualMachines/jdk1.8.0_144.jdk/Contents/Home as a path you will get the literal expression $(/usr/libexec/java_home).

Make sure to evaluate it before setting the environment variable, like so:

from os import environ
from subprocess import Popen, PIPE

bash_variable = "$(/usr/libexec/java_home)"
capture = Popen(f"echo {bash_variable}", stdout=PIPE, shell=True)
std_out, std_err = capture.communicate()
return_code = capture.returncode

if return_code == 0:
    evaluated_env = std_out.decode().strip()
    environ["JAVA_HOME"] = evaluated_env
else:
    print(f"Error: Unable to find environment variable {bash_variable}")

Answer 5

if i do os.environ["DEBUSSY"] = 1, it complains saying that 1 has to be string.

Then do

os.environ["DEBUSSY"] = "1"

I also want to know how to read the environment variables in python(in the later part of the script) once i set it.

Just use os.environ["DEBUSSY"], as in

some_value = os.environ["DEBUSSY"]

Answer 6

Environment variables must be strings, so use

os.environ["DEBUSSY"] = "1"

to set the variable DEBUSSY to the string 1.

To access this variable later, simply use:

print(os.environ["DEBUSSY"])

Child processes automatically inherit the environment variables of the parent process -- no special action on your part is required.