How to get line number of function (with/without a decorator) in a python module?

There is no easy solution in the general case.

A decorator is a function that given a function returns a function, normally by "wrapping" it in a closure that performs the operation for which the decorator has been designed.

The file and line number information are not however in the function object itself and you cannot "fix" them by copying this information from the wrapped function to the wrapper. That data is instead contained in the code object of the function (available with .func_code), and it is shared among all closures you are going to create.

>>> def bar(x):
...     def foo():
...         return x
...     return foo
... 
>>> f1 = bar(1)
>>> f2 = bar(2)
>>> f1()
1
>>> f2()
2
>>> f1.func_code is f2.func_code
True
>>> 

The wrapt module solves this problem by allowing you to write decorators which preserve the necessary metadata to find the source of a function as well as perform other introspection. It's like an improved functools.wraps.