How come I didn’t know about the python -m pydoc command before today!

It lets you inspect the docstrings of any modules, classes, functions, or methods in Python.

I’m running the commands from a Python 3.10 virtual environment but it’ll work on any Python version. Let’s print out the docstrings of the functools.lru_cache function. Run:

python -m pydoc functools.lru_cache

This will print the following on the console:

Help on function lru_cache in functools:

functools.lru_cache = lru_cache(maxsize=128, typed=False)
    Least-recently-used cache decorator.

    If *maxsize* is set to None, the LRU features are disabled and
    the cache can grow without bound.

    If *typed* is True, arguments of different types will be cached
    separately. For example, f(3.0) and f(3) will be treated as
    distinct calls with distinct results.

    Arguments to the cached function must be hashable.

    View the cache statistics named tuple (hits, misses, maxsize,
    currsize) with f.cache_info().  Clear the cache and statistics
    with f.cache_clear(). Access the underlying function with
    f.__wrapped__.

Works for third party tools as well:

python -m pydoc typing_extensions.ParamSpec

Also, works for any custom Python structure that is accessible from the current Python path. Let’s define a function with docstrings and put that in a module called src.py:

# src.py
def greetings(name: str) -> None:
    """Prints Hello <name>! on the console.

    Parameters
    ----------
    name : str
        Name of the person you want to greet
    """

    print("Hello {name}!")

You can inspect the entire src.py module or the greetings function specifically as follows:

To inspect the module, run:

python -m pydoc src

To inspect the greetings function only, run:

python -m pydoc src.greetings

It’ll return:

Help on function greetings in src:

src.greetings = greetings(name: str) -> None
    Prints Hello <name>! on the console.

    Parameters
    ----------
    name : str
        Name of the person you want to greet

Instead of inspecting the docstrings one by one, you can also pull up all of them in the current Python path and serve them as HTML pages. To do so, run:

python -m pydoc -b

This will render the docstrings as HTML web pages and automatically open the index page with your default browser. From there you can use the built-in search to find and read your ones you need.

Recent posts

  • ETag and HTTP caching
  • Crossing the CORS crossroad
  • Dysfunctional options pattern in Go
  • Einstellung effect
  • Strategy pattern in Go
  • Anemic stack traces in Go
  • Retry function in Go
  • Type assertion vs type switches in Go
  • Patching pydantic settings in pytest
  • Omitting dev dependencies in Go binaries