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gh-156491: Avoid KeyErrors in os._Environ.get() and __contains__() #156492

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gh-156491: Avoid KeyErrors in os._Environ.get() and __contains__() #156492

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39193be
Avoid KeyErrors in os._Environ.get() and __contains__()
alexmalyshev Aug 27, 2026
d13030b
Switch to using a sentinel()
alexmalyshev Aug 27, 2026
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12 changes: 12 additions & 0 deletions Lib/os.py
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Original file line number Diff line number Diff line change
Expand Up @@ -720,6 +720,11 @@ def get_exec_path(env=None):
# Change environ to automatically call putenv() and unsetenv()
from _collections_abc import MutableMapping, Mapping

# Sentinel used for seeing if a value is found within the internal _Environ
# dictionary.
_MISSING = sentinel("MISSING")


class _Environ(MutableMapping):
def __init__(self, data, encodekey, decodekey, encodevalue, decodevalue):
self.encodekey = encodekey
Expand All @@ -728,6 +733,9 @@ def __init__(self, data, encodekey, decodekey, encodevalue, decodevalue):
self.decodevalue = decodevalue
self._data = data

def __contains__(self, key):
return self.encodekey(key) in self._data

def __getitem__(self, key):
try:
value = self._data[self.encodekey(key)]
Expand Down Expand Up @@ -770,6 +778,10 @@ def __repr__(self):
def copy(self):
return dict(self)

def get(self, key, default = None):
val = self._data.get(self.encodekey(key), _MISSING)
return default if val is _MISSING else self.decodevalue(val)

def setdefault(self, key, value):
if key not in self:
self[key] = value
Expand Down
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