如何查找Python内置map()函数的源代码？PyCharm跳转仅显示pass

Hey there! I totally get why this feels frustrating—you try to dive into how Python's built-in map() works in PyCharm, but all you get is a placeholder with pass instead of actual logic. Let's break this down step by step.

Why PyCharm Shows a Stub Instead of Real Code #

Most of Python's core built-in functions (like map(), filter(), and zip()) are implemented in C for performance, not pure Python. The "definition" you see in PyCharm comes from a type stub file (usually builtins.pyi), which is just a lightweight placeholder. These stubs exist only to give your IDE type hinting and autocompletion—they don't contain the actual execution logic.

Here's what that stub might look like for map():

def map(func: Callable[[Any], Any], *iterables: Iterable[Any]) -> Iterator[Any]:
    pass

Or sometimes it uses ellipses (...) instead of pass, but either way, it's not the real implementation.

How to Find the Actual C Source Code for map() #

Since map() is part of CPython (the standard Python implementation), you can find its source in the official CPython codebase:

• Locate the right file: The map() function is implemented as an iterator object in Objects/iterobject.c. Look for the PyMap_Type struct and related functions like map_new (handles initialization) and map_iternext (handles producing the next value in the iteration).
• Match your Python version: Make sure you're looking at the source code for the exact Python version you're using—implementation details can change between versions.
• Local access: If you prefer to browse locally, download the source code archive for your Python version, then navigate to the Objects/ directory and open iterobject.c.

Bonus: A Pure Python Equivalent to Understand the Logic #

If you just want to grasp how map() works under the hood without digging into C code, here's a simplified pure Python implementation that mirrors the core logic:

def my_map(func, *iterables):
    # Convert all input iterables to iterators
    iterators = tuple(iter(it) for it in iterables)
    while True:
        try:
            # Get the next value from each iterator
            args = tuple(next(it) for it in iterators)
            # Apply the function and yield the result
            yield func(*args)
        except StopIteration:
            # Exit when any iterator is exhausted
            return

This behaves just like the built-in map()—it applies the function to corresponding elements from each iterable until one of them runs out.

内容的提问来源于stack exchange，提问作者Bonderson