Why python uppercases all environment variables in windows

Question

Is there any reason why os.environ contains all environment variables uppercase on Windows?, I don\'t understand why (only on windows) it doesn\'t load them on using the sam

Answer 1

Because Windows environment variables are case insensitive, but a Python dictionary is case sensitive. By uppercasing all entries, you ensure that you'll always be able to match entries.

Quoting from the Python os.py source code:

elif name in ('os2', 'nt'):  # Where Env Var Names Must Be UPPERCASE
    # But we store them as upper case

# ... 

else:  # Where Env Var Names Can Be Mixed Case

Note that the os.environ object translates all access to uppercase, including searches:

def __setitem__(self, key, item):
    putenv(key, item)
    self.data[key.upper()] = item
def __getitem__(self, key):
    return self.data[key.upper()]

# ...

def has_key(self, key):
    return key.upper() in self.data
def __contains__(self, key):
    return key.upper() in self.data
def get(self, key, failobj=None):
    return self.data.get(key.upper(), failobj)

This means that if a program fails to find os.environ['windir'], then the value is not set.

If you have to have access to the original values, grab them from the nt module:

import nt
nt.environ

That's the raw initial dictionary as passed in by the OS, unaltered:

>>> import nt
>>> sorted(nt.environ.keys())
['ALLUSERSPROFILE', 'APPDATA', 'COMPUTERNAME', 'ComSpec', 'CommonProgramFiles', 'CommonProgramFiles(x86)', 'CommonProgramW6432', 'FP_NO_HOST_CHECK', 'HOMEDRIVE', 'HOMEPATH', 'LOCALAPPDATA', 'LOGONSERVER', 'NUMBER_OF_PROCESSORS', 'OS', 'PATHEXT', 'PROCESSOR_ARCHITECTURE', 'PROCESSOR_IDENTIFIER', 'PROCESSOR_LEVEL', 'PROCESSOR_REVISION', 'PROMPT', 'PSModulePath', 'PUBLIC', 'Path', 'ProgramData', 'ProgramFiles', 'ProgramFiles(x86)', 'ProgramW6432', 'SESSIONNAME', 'SSH_AUTH_SOCK', 'SystemDrive', 'SystemRoot', 'TEMP', 'TMP', 'USERDNSDOMAIN', 'USERDOMAIN', 'USERNAME', 'USERPROFILE', 'windir', 'windows_tracing_flags', 'windows_tracing_logfile']