The Python Standard Library

Python ships with a large standard library.

It includes modules for working with files, dates, JSON, databases, networking, testing, logging, and much more. You do not install these modules from PyPI before importing them.

Use the standard library reference for the Python version you run. Module availability can vary by platform and distribution. For example, tkinter depends on Tcl/Tk being available.

Built-ins, the standard library, and third-party packages

These three groups are related, but they are not the same:

• Built-in functions and types such as print(), len(), str, and list are available without an import.
• Standard library modules ship with Python and normally need an import.
• Third-party packages are installed separately, usually from the Python Package Index.

For example, requests is a popular third-party HTTP package. It is not part of the standard library. Python’s standard library includes urllib.request for opening URLs.

Useful standard library modules

Here are some modules worth knowing:

• math for math utilities
• re for regular expressions
• json to work with JSON
• datetime to work with dates
• pathlib to work with filesystem paths
• sqlite3 to use SQLite
• os and sys for operating system and interpreter functionality
• collections for specialized container data types
• itertools and functools for iteration and function tools
• subprocess to start and communicate with other programs
• logging for application logs
• unittest for automated tests
• venv to create virtual environments
• random for simulations and other non-security uses
• secrets for security-sensitive random values
• statistics for statistics utilities
• urllib.request to open URLs

The random documentation explicitly recommends secrets for cryptographic and security uses.

How to import a module

You import a standard library module in the same way you import code from another module:

import math

result = math.sqrt(4)
print(result)  # 2.0

You can also import a specific name:

from math import sqrt

result = sqrt(4)
print(result)  # 2.0

Importing the module is often clearer because math.sqrt() immediately tells the reader where sqrt() came from.

Here is a small HTTP example using only the standard library:

from urllib.request import urlopen

with urlopen("https://www.python.org/", timeout=10) as response:
    html = response.read()

print(len(html))

For a real application, also handle network errors and decide how much response data you are willing to read.

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