[Python] Using `setattr` to decorate functions from another module

I'm having trouble applying a decorator to an imported function. Suppose I have the following foo.py module:

# contents of foo.py
def bar():
return "hello"


I now want to import bar from it and apply the lru_cache decorator, so in my main file I do this:

from functools import lru_cache
import foo

def main():
# caching foo.bar works fine
for _ in range(2):
if hasattr(foo.bar, "cache_info"):
print("bar is already cached")
else:
print("caching bar")
setattr(foo, "bar", lru_cache(foo.bar))

if __name__ == "__main__":
main()


which produces, as expected, the following output:

caching bar
bar is already cached


However, I don't want to import the whole foo module, so now I only import bar and rely on sys.modules to find out where bar comes from. Then main.py becomes:

from functools import lru_cache
import sys
from foo import bar

def main():
for _ in range(2):
if hasattr(bar, "cache_info"):
print("bar is already cached")
else:
print("caching bar")
setattr(sys.modules[__name__], "bar", lru_cache(bar))


if __name__ == "__main__":
main()


Again, this produces the wanted output:

caching bar
bar is already cached


But now I want my decorating process to be reusable in several modules, so I write it as a function in file deco.py:

from functools import lru_cache
import sys

def mydecorator(somefunction):
for _ in range(2):
if hasattr(somefunction, "cache_info"):
print(f"{somefunction.__name__} is already cached")
else:
print(f"caching {somefunction.__name__}")
setattr(sys.modules[somefunction.__module__], "bar", lru_cache(somefunction))


And so main.py becomes:

import sys
from foo import bar
from deco import mydecorator

def main():
mydecorator(bar)

if __name__ == "__main__":
main()


This time the decoration fails; the output becomes:

caching bar
caching bar # <- wrong; should be cached already


How do I correct my code?

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