In this article we will explore some lesser known, but interesting and useful corners of Python standard library.

Python dictionaries and lists are bread and butter for many applications, but might be too simple for more advanced data organisation. To provide more powerful containers for storing data in memory Python ships a collection module with things like:

• Deque - list-like data structure for efficient insertion and removal of items from either end.
• Counter - subclass of dictionary to count stuff.
• ChainMap - meta-dictionary that provides unified key-value mapping across multiple dictionaries without copying the data.
• Advanced structures for data mappings:
  • OrderedDict - dictionary that maintains order of key-value pairs (e.g. when HTTP header value matters for dealing with certain security mechanisms).
  • namedtuple - a factory function that creates a subclass of tuple with named fields. Could be convenient for more OOP approach than just using dict.
  • defaultdict - dictionary with some or all or the values pre-filled. Could be handy when you want to provide values for fields that may be missing in web pages being scraped.
• UserDict, UserList and UserString - wrappers for dict, list and str for further subclassing.

API reference: https://docs.python.org/3/library/collections.html

Python has with keyword to create context manager that will auto-cleanup things within lexical scope. For example, you don’t have to worry about closing a file yourself if you open it like this:

with open("results.txt", "w") as out_f:
    out_f.write("...\n")
    ...

contextlib module provide helpers to work with context managers in your code. For example, you can use @contextmanager annotation to turn your own function into one that could be used via with syntax.

API reference: https://docs.python.org/3/library/contextlib.html

Due to technical reality of how floating point number are represented, floating point computations can have some weird results:

>>> 0.1 + 0.1 + 0.1 - 0.3
5.551115123125783e-17
>>> 1.2 + 2.2
3.4000000000000004

This is mathematically incorrect and a deal breaker for some applications, such as those dealing with money. To address this problem, Python ships decimal module that allows us represent decimal numbers as Python objects with operator overloading. Computations are adjusted so that we get the correct result (within a configurable level of precision):

>>> from decimal import *
>>> one_point_two = Decimal('1.2')
>>> one_point_two
Decimal('1.2')
>>> two_point_two = Decimal('2.2')
>>> two_point_two
Decimal('2.2')
>>> one_point_two + two_point_two
Decimal('3.4')

API reference: https://docs.python.org/3/library/decimal.html

Likewise, we can run into problem when dealing with fractions - one third is not exactly equal to 0.333… Python ships with fractions module to represent them as Python objects with operator overloading:

>>> import fractions
>>> one_third = fractions.Fraction(numerator=1, denominator=3)
>>> 2 * one_third
Fraction(2, 3)

API reference: https://docs.python.org/3/library/fractions.html

Python interpreter is implemented as stack machine internally. When you run some Python code it is compiled to Python-specific bytecode that Python VM executes. For debugging or performance optimisation purposes it might be desirable to disassemble Python bytecode into instruction. The standard Python installation ships with dis module that takes Python code units (e.g. a function) and disassembles the code into a kind of pseudo-assembler:

>>> import dis
>>> def add(a, b):
...     return a+b
... 
>>> dis.dis(add)
  1           0 RESUME                   0

  2           2 LOAD_FAST                0 (a)
              4 LOAD_FAST                1 (b)
              6 BINARY_OP                0 (+)
             10 RETURN_VALUE

API reference: https://docs.python.org/3/library/dis.html

Python statistics module provides a small toolkit of statistical algorithms for relatively simple applications where it is an overkill to use Pandas or Numpy: standard deviation, several kinds of average of numeric data, linear regression, correlation, normal distribution and others. For people eager to join the AI/ML revolution it provides Naive Bayes classifier - an algorithm that can be considered a minimum viable example of machine learning.

API reference: https://docs.python.org/3/library/statistics.html

You may sometimes want to open web browser from your Python code. Since Python is portable and multiplatform language this may be bit of hassle due to differences between platforms and setups. To make this easier Python ships a webbrowser module with simple API to make a browser show a page. For example, we can call open_new() function with URL:

>>> import webbrowser
>>> webbrowser.open_new('https://trickster.dev')
True

If you want to open a local file (e.g. HTML report with results of some automation) you need to pass a file URL to one of the functions:

>>> import os
>>> file_url = 'file://' + os.path.realpath('test.html')
>>> webbrowser.open(file_url)
True

API reference: https://docs.python.org/3/library/webbrowser.html

Distributing Python programs in source code form can be problematic if there’s some non-technical users at the receiving end. Even if they have Python installed there can be lacking dependencies, version conflicts and other runtime issues. To make this less terrible Python ships zipapp module with CLI tool and Python API to package Python code into single file packages. This provides an interesting midpoint between using virtual environments and solutions like PyInstaller to compile the app into platform-specific form - code remains portable, but Python interpreter has to be there to run it.

API reference: https://docs.python.org/3/library/zipapp.html