Python read all environment variables

Reading and writing environment variables in Python? [duplicate]

My python script which calls many python functions and shell scripts. I want to set a environment variable in Python (main calling function) and all the daughter processes including the shell scripts to see the environmental variable set. I need to set some environmental variables like this:

1 is a number, not a string. Additionally, how can I read the value stored in an environment variable? (Like DEBUSSY / FSDB in another python child script.)

What’s with the «DEBUSSY» thing? It was in the duplicate thread too. Google just brings up info on some French guy.

@David What. Okay, so my «French» comment was pointless, yes, but I’m still wondering what this DEBUSSY thing is.

Sorry guys, if i sounded lazy. The reason i got very less time to modify the scripts and so i am resorting to the forums. I like reading books. Just that lack of time is prompting me to find quick solutions on forums

DEBUSSY is a tool which helps us to view waveforms while designing hardware systems. I used the real world example. I design Hardware systems but we use lot of scripting languages to automate the tool flow

4 Answers 4

import os os.environ['DEBUSSY'] = '1' os.environ['FSDB'] = '1' # Open child processes via os.system(), popen() or fork() and execv() someVariable = int(os.environ['DEBUSSY']) 

See the Python docs on os.environ . Also, for spawning child processes, see Python’s subprocess docs.

When I try this approach in mac os, the environment variables aren’t available from the shell. only python can read the environment variables set this way.

@openCivilisation That is correct, it should be impossible for a script to modify the calling shell’s environment for security reasons (imposed by the shell, not python)

@BND I guess it is written somewhere in the docs of the shell (e.g. Bash). I only know that limitation as a «core principle» like «you cannot edit file modes on files you don’t own»

First things first 🙂 reading books is an excellent approach to problem solving; it’s the difference between band-aid fixes and long-term investments in solving problems. Never miss an opportunity to learn. 😀

You might choose to interpret the 1 as a number, but environment variables don’t care. They just pass around strings:

 The argument envp is an array of character pointers to null- terminated strings. These strings shall constitute the environment for the new process image. The envp array is terminated by a null pointer. 

You access environment variables in python using the os.environ dictionary-like object:

>>> import os >>> os.environ["HOME"] '/home/sarnold' >>> os.environ["PATH"] '/home/sarnold/bin:/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin:/usr/games' >>> os.environ["PATH"] = os.environ["PATH"] + ":/silly/" >>> os.environ["PATH"] '/home/sarnold/bin:/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin:/usr/games:/silly/' 

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Python Read Environment Variable

Python environment variables are utilized to change the system configuration, and the output of many python applications depends on the values of the environment variables. Even environment variables help you to write smoother workflows. They are accessed via the os module in Python.

Python environment variables make code more secure by masking sensitive data needed to assign environment variables, such as API tokens.

What is Environment Variable in Python

Python environment variables exist outside your code and as part of your current user’s or system’s configuration. Environment variables characterize key-value pairs of data where the key is the environment variable name, and the value is the environment variable value that can be accessed through your code.

Python Environment Variables help you write more streamlined and secure code because the important data can be saved inside the environment variable and the script file shared without worrying about exposing sensitive information.

Python read environment Variables can be read and set with the help of functions provided by OS modules which help to interact with the operating system.

Reading Environment Variable in Python

Reading Python environment variables requires the import of the os module. Os module provides an environ property to get or read the dictionary of all the python environment variables.

Suppose you want to read all the python environment variables, which can be possible with os.environ .

The above code illustrates that we’re importing the os module with the help of the import statement and then printing the environment variables with the use of the print() function and os.environ method to get the Python read environment Variable.

The below image shows a dictionary of python variable environments as key-value pairs.

The above output of os.environ as a dictionary could be more precise. Let’s make it better visually by looping through the dictionary and printing the keys and values.

We are getting the python environment variable dictionary in the above code and looping through it to print the key-value pairs.

More Examples for Understanding

In the above, We looked at dictionary examples of all Python environment variables, but you can also read the value of a specific environment variable value.

In the above, we get the PATH environment variable’s value, store it inside the path variable, and print it to display the value.

FAQs

1. What is the PATH Variable Used For?

PATH is an environment variable in Windows that tells the interpreter where to find the module files imported into the program.

2. How do I Add an Environment Variable?

You can add environmental variables using the os.environ method using the os.environ[«key»] = «value» syntax.

3. Is os.environ the Only Method to Change the Environment Variable?

No, You can also change the environment variables manually by changing your system python variables configuration.

Conclusion

• The value pairs of the environment variables can be set or read by utilizing the os.environ of the os module.
• Environment variables provide the capability to run your code securely.
• Environment variables allow you to streamline your code without repeating and changing it. Likewise, they prevent you from sharing secure items such as API Keys.

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How to get and set environment variables in Python

Environment variables are used to change the system configuration. The output of the many Python applications depends on the values of the particular environment variables. When those environment variables change, the python script requires changing to get the appropriate output, which is not desirable. This problem can be solved by reading and setting the value of the environment variable in the Python script based on the requirement. It eliminates the task of changing the environment variable manually and makes the code more secure by hiding the sensitive data required to assign the environment variable, such as API token. The ways to set and get the environment variable in Python have shown in this tutorial.

Read Environment Variables in Python:

The os module will require to import to read the environment variables. The os.environ object is used in Python to access the environment variable. The coder can set and get the value of any environment variable by using this object. Different ways to read, check and assign the value of the environment variable have shown in the next part of this tutorial.

Example-1: Read all and specific environment variable

Create a python file with the following script to read and print all variables and the specific environment variable. The ‘for’ loop has used in the script to read and print all existing environment variable names and values. Next, the value of the ‘HOME’ variable has been printed.

# Import os module
import os

# Iterate loop to read and print all environment variables
print ( «The keys and values of all environment variables:» )
for key in os . environ :
print ( key , ‘=>’ , os . environ [ key ] )

# Print the value of the particular environment variable
print ( «The value of HOME is: » , os . environ [ ‘HOME’ ] )

Output:

The following output will appear after executing the above script. The list of all environment variables has been printed, and the value of the HOME variable has been printed at the end of the output.

Example-2: Check the specific environment variable is set or not

Create a python file with the following script to check the particular environment variable is set or not. Here, the os module has been used to read the values of the particular environment variable, and the sys module has been used to terminate from the script. The infinite ‘while’ loop has continuously checked the value of the specific environment variable continuously until the user provides a variable name that is not set. If the user provides an environment variable name as input, then the value of that variable will be printed. If the user provides an

# Import os module
import os
# Import sys module
import sys

while True :
# Take the name of the environment variable
key_value = input ( «Enter the key of the environment variable:» )

# Check the taken variable is set or not
try :
if os . environ [ key_value ] :
print ( «The value of» , key_value , » is » , os . environ [ key_value ] )
# Raise error if the variable is not set
except KeyError :
print ( key_value , ‘environment variable is not set.’ )
# Terminate from the script
sys . exit ( 1 )

Output:

After executing the above script, the following output will appear if the variable name taken is set for the first input value and not set for the second input value. According to the output, the value of the HOME variable is set, and the value of this variable has been printed. Next, the API_KEY has taken as the variable that is not set. So, the script has terminated after displaying the message.

Example-3: Check the particular environment variable is on or off

Create a python file with the following script to check a particular environment variable is on or off. The get() function has been used in the script to check the current value of the ‘DEBUG’ is True or False. The script will print the message based on the value of the variable.

# Import os module
import os

# Checking the value of the environment variable
if os . environ . get ( ‘DEBUG’ ) == ‘True’ :
print ( ‘Debug mode is on’ )
else :
print ( ‘Debug mode is off’ )

Output:

The following output will appear after executing the above script if the value of the DEBUG variable is False. The variable’s value can be changed by using the setdefault() function shown in the next example.

Example-3: Assign the value to the environment variable

The setdefault() function is used to set the value of any environment variable. Create a python file with the following script to enable the environment variable, ‘DEBUG’, that is disabled by default. The value of this variable has been enabled at the beginning of the script by setting the value to True using the setdefault() function. Next, the value of this variable has checked by using the get() function. The message, ‘Debug mode is on’ will be printed if the variable is set properly; otherwise, the message, ‘Debug mode is off’ will be printed.

# Import os module
import os

# Set the value DEBUG variable
os . environ . setdefault ( ‘DEBUG’ , ‘True’ )

# Checking the value of the environment variable
if os . environ . get ( ‘DEBUG’ ) == ‘True’ :
print ( ‘Debug mode is on’ )
else :
print ( ‘Debug mode is off’ )

Output:

The following output will appear after executing the above script. The ‘DEBUG’ variable has been enabled by using setting its value to True. So, the message, ‘Debug mode is on’ has printed as the output.

Conclusion:

The values of the environment variables can be set or get by using environ[] array of the os module or by using the setdefault() and the get() functions. The name of the environment variable is used as the index of the environ[] array to set or get the value of that variable. The get() function is used to get the value of a particular variable, and setdefault() function is used to set the value of the particular variable.

About the author

Fahmida Yesmin

I am a trainer of web programming courses. I like to write article or tutorial on various IT topics. I have a YouTube channel where many types of tutorials based on Ubuntu, Windows, Word, Excel, WordPress, Magento, Laravel etc. are published: Tutorials4u Help.

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