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 I do  os environ  quot DEBUSSY quot     1  it complains saying that 1 has to be a string  I also want to know how to read the environment variables in Python  in the latter part of the script  once I set it

User · Answer

When you play with environment variables (add/modify/remove variables), a good practice is to restore the previous state at function completion.

You may need something like the modified_environ context manager describe in this question to restore the environment variables.

Classic usage:

with modified_environ(DEBUSSY="1"):
    call_my_function()

User · Answer

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

User · Answer

Use setdefault function to set a new variable if the variable does not exist in the environment  make sure you set the environment variable as a string  not int  Otherwise will throw  TypeError  import os  if not os environ get  quot DEBUSSY quot        os environ setdefault  quot DEBUSSY quot   quot 1 quot   else       os environ  quot DEBUSSY quot      quot 1 quot   print os environ  quot DEBUSSY quot

User · Answer

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  lt   gt  strauss   os environ  STRAUSS   debussy   int os environ get  DEBUSSY    -1     print   s  u   s  u      Strauss   strauss   Debussy   debussy

User · Answer

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

User · Answer

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

User · Answer

You should assign string value to environment variable    os environ  DEBUSSY      1   If you want to read or print the environment variable just use    print os environ  DEBUSSY      This changes will be effective only for the current process where it was assigned  it will no change the value permanently  The child processes will automatically inherit the environment of the parent process

User · Answer

to Set Variable   item Assignment method using key   import os     os environ  DEBUSSY      1    Environ Variable must be string not Int   to get or to check whether its existed or not   since os environ is an instance you can try object way   Method 1   os environ get  DEBUSSY     this is error free method if not will return None by default   will get  1  as return value  Method 2   os environ  DEBUSSY     will throw an key error if not found    Method 3    DEBUSSY  in os environ    will return Boolean True False   Method 4   os environ has key  DEBUSSY    last 2 methods are Boolean Return so can use for conditional statements

User · Answer

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

User · Answer

os environ behaves like a python dictionary  so all the common dictionary operations can be performed  In addition to the get and set operations mentioned in the other answers  we can also simply check if a key exists  The keys and values should be stored as strings   Python 3  For python 3  dictionaries use the in keyword instead of has key    gt  gt  gt  import os  gt  gt  gt   HOME  in os environ    Check an existing env  variable True       Python 2   gt  gt  gt  import os  gt  gt  gt  os environ has key  HOME      Check an existing env  variable True  gt  gt  gt  os environ has key  FOO       Check for a non existing variable False  gt  gt  gt  os environ  FOO      1        Set a new env  variable  String value   gt  gt  gt  os environ has key  FOO   True  gt  gt  gt  os environ get  FOO           Retrieve the value  1    There is one important thing to note about using os environ   Although child processes inherit the environment from the parent process  I had run into an issue recently and figured out  if you have other scripts updating the environment while your python script is running  calling os environ again will not reflect the latest values   Excerpt from the docs      This mapping is captured the first time the os module is imported    typically during Python startup as part of processing site py  Changes   to the environment made after this time are not reflected in   os environ  except for changes made by modifying os environ directly    os environ data which stores all the environment variables  is a dict object  which contains all the environment values    gt  gt  gt  type os environ data     changed to  data since v3 2  refer comment below   lt type  dict  gt

User · Answer

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

User · Answer

What about os environ  DEBUSSY      1   Environment variables are always strings

[python] How to set environment variables in Python?

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