Libraries

Libraries allow us to apply Python to real tasks. These are a few popular ones, but there are many.

Utilities

• collections

  Specialized containers: counting items, grouping with defaults, named tuples, fast queues.

  Counter: + - & | counts[item] elements most_common subtract total update

  defaultdict: default_factory get

  namedtuple: _asdict _field_defaults _fields _make _replace defaults=

  deque: append appendleft clear copy count extend extendleft index insert maxlen= pop popleft remove reverse rotate

  OrderedDict: == move_to_end popitem

  ChainMap: maps new_child parents

  User* wrapper: UserDict UserList UserString

• datetime

  Calculating and formatting dates and times.

  date: creating a specific date strftime

  timedelta: difference between two dates strptime

• math

  Rounding, roots, constants, and logarithms.

  floor: ceil trunc

  sqrt: isqrt pow

  pi: inf nan

  log2: exp log10

  isclose

• random

  Random numbers, random picks, shuffled order.

  randint

  choice: sample shuffle

• re

  Regular expressions: searching, extracting, and replacing text by pattern.

  search: compile

  findall: groups named groups

  sub

  split

• time

  Reading the system clock, pausing execution, and measuring elapsed time.

  time

  sleep

  perf_counter

  localtime: strftime

Data analysis

• csv

  Reading and writing spreadsheets.

  writer

  reader: DictReader

• matplotlib

  Charts and plots: line, bar, and scatter, built directly from plain Python data.

  line plots: labels and title multiple lines and a legend

  bar charts

  scatter plots

  subplots

  saving a figure

• NumPy

  Fast numeric arrays, with math applied to a whole array at once instead of item by item.

  ndarray: arange

  array operations: boolean mask mean

• pandas

  Tabular data: rows and columns, like a spreadsheet, built on top of NumPy.

  DataFrame

  working with a DataFrame: mean sort_values

APIs

• json

  Reading and writing JSON data: nested dicts and lists, saved to a file or a string.

  dump

  load: nested data

  loads

• requests

  Fetching data over the internet, like asking a website or API for information.

  how requests work

  get: headers json params status_code

  post

  error handling

Web

• BeautifulSoup

  Parsing HTML: finding tags, reading attributes and text, and turning a page into structured data.

  HTML and web pages

  Parsing HTML: Finding tags Reading text and attributes

  Extracting structured data

  Putting it together: Common tasks Scraping a real page

Images

• Pillow

  Opening, editing, and saving images, built around one Image object.

  why Pillow?

  Image: basic operations crop image modes opening and saving images resize rotate and flip

  ImageOps: common ImageOps functions

  ImageDraw: shapes and lines

  ImageFont: loading a font

  ImageColor: converting color names

  ImageFilter: applying a filter

  ImageEnhance: enhancing an image

  ImageChops: comparing and combining images

  convert: converting between formats

  ImageSequence: looping over GIF frames

  putting it together: an interactive filter tool

Computer vision

• OpenCV

  Real-time image and video analysis, built directly on NumPy arrays: color spaces, edge detection, face detection.

  reading, displaying, saving images: displaying a window imread saving a file

  color spaces: cvtColor

  basic operations: cropping resize rotating

  drawing: shapes and lines text

  thresholding, edge detection: Canny threshold

  blurring: gaussian blur

  contours: finding and drawing contours

  CascadeClassifier: detecting and labeling faces

  VideoCapture: reading frames

Desktop UIs

• Tkinter

  Creating desktop applications: text, buttons, dropdowns, forms, output, etc.

  Tk

  Button: Button Entry Label

  pack: grid pack

  configure: reading and changing options

  command: binding events command callbacks

  Style: customizing a style

  messagebox: file dialogs message boxes

  winfo_width: winfo methods

  putting it together: a simple form

Games

• turtle

  Build small movement-based games with a pen cursor.

  Concepts

  Screen: Background Clear Close Colors Setup

  turtle cursor: Appearance Circle Color Custom images Dot Drawing shapes Hide Ink Motion Positions Rectangle Shape Show Size Stamping Text Tracer

  Game loop: done()

  Input: Dialog prompts Keyboard Mouse

  inside: Distance Membership Overlap

  Common patterns

Testing

• pytest

  Writing and running tests: assertions, fixtures, and parametrizing.

  writing and running a test: from the command line

  reading a failure

  fixtures

  parametrizing tests

  testing for exceptions