source cshrc file in python

Question

I have to source a cshrc file from python and store the environment variables set by the cshrc file only in a dictionary. I am using this:

output = subprocess.check_output(
    f'''source {file}; python -c "import os, json; 
print(json.dumps(dict(os.environ)))"''',
    shell=True, executable='/bin/csh')
env = json.loads(output)

However, this also prints these variables:

{'VENDOR': 'unknown', 'SHLVL': '1', 'PWD': <>, 'HOSTTYPE': 'x86_64-linux', 'HOST': <>, 
'LOGNAME': <>, 'USER': <>, 'OSTYPE': 'linux', 'GROUP': 'users', 'MACHTYPE': 'x86_64', 
variables_from_file}

How do I ensure only those variables are returned that are there from the file? I cannot filter out the above variables cause what if they are actually there in the file. I tried cleaning up environment before calling the subprocess but that also didn't work.

Any help would be appreciated?