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How to Access Built-in Function Documentation in Python

Python is known for its "batteries included" philosophy, offering a vast standard library and numerous built-in functions like print(), len(), and sorted(). However, remembering every parameter and behavior for these functions is impossible.

This guide explains how to access Python's built-in documentation directly from your code or interactive shell using the help() function and the __doc__ attribute.

Using the Interactive help() Function​

The most direct way to read documentation is the built-in help() function. It invokes the interactive help system, which formats the text, arguments, and descriptions for readability.

Correct Usage​

You must pass the function object itself to help(), not the result of calling the function.

# ✅ Correct: Pass the function name without parentheses
help(print)

Output (Truncated):

Help on built-in function print in module builtins:

print(...)
    print(value, ..., sep=' ', end='\n', file=sys.stdout, flush=False)
    
    Prints the values to a stream, or to sys.stdout by default.
    Optional keyword arguments:
    file:  a file-like object (stream); defaults to the current sys.stdout.
    sep:   string inserted between values, default a space.
    ...

Common Mistake: Calling the Function​

If you add parentheses (), Python executes the function first and then asks for help on the return value.

# ⛔️ Incorrect: This executes print(), which returns None, 
# so you get help on the 'NoneType' object instead of the print function.
help(print())

Output:

Help on NoneType object:

class NoneType(object)
 |  Methods defined here:
 |  
 |  __bool__(self, /)
 |      True if self else False
 ...
tip

To exit the help viewer in a terminal or command prompt, press the q key.

Accessing Raw Docstrings via __doc__​

Every Python object has a __doc__ dunder (double underscore) attribute. This attribute contains the raw documentation string (docstring). This is useful if you want to print the documentation programmatically without entering the interactive help mode.

# ✅ Correct: Accessing the __doc__ attribute
doc_string = len.__doc__
print(doc_string)

Output:

Return the number of items in a container.
note

The __doc__ attribute contains the raw text exactly as it was written in the source code. help() cleans this up and adds metadata (like the module name).

Understanding Function Signatures​

When you access documentation, the most critical part is the Signature, i.e. the line defining the parameters.

Example signature from help(sorted): sorted(iterable, /, *, key=None, reverse=False)

  • iterable: A required argument (e.g., a list).
  • /: Arguments before this must be positional only.
  • *: Arguments after this must be keyword arguments (named).
  • reverse=False: An optional argument with a default value.
# Based on the documentation for 'sorted' found via help(sorted)

data = [3, 1, 2]

# ✅ Correct: Using keyword arguments as described in docs
sorted_data = sorted(data, reverse=True)
print(sorted_data)

Output:

[3, 2, 1]

Conclusion​

To effectively use Python's built-in functions:

  1. Use help(function_name) in the interactive shell for a readable, detailed manual.
  2. Use print(function_name.__doc__) for a quick, programmatic check of what a function does.
  3. Do not call the function inside help(); pass the object directly.

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