Refactoring is one of PyCharm's most powerful features and its capabilities go beyond a single file. One of the simplest ways to see this feature at work is renaming a variable or a function:

def add_one(n):
    return n + 1


def foo(func, n):
    return func(n)


foo(add_one, 2)

In the preceding example, we want to change the function name foo to apply (because it makes more sense). This is of course a simple example, but helps prove a point.

This brings up another window that gives us a few options:

Here, [1] is very useful if we have put docstrings into the functions that describe variables. [2] will search for text documents such as .rst and .md. This already shows you how far PyCharm can...