- Python 3 Cheat Sheet Introduction to Python 3 Cheat Sheet Python is a high-level programming language that was designed by Guido Van Rossum and developed by the Python software foundation in 1990. It has a paradigm of Object-oriented, imperative and procedural reflective.
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This document is a quick cheat sheet showing how the PEP 484 typeannotation notation represents various common types in Python 3.
Note
Technically many of the type annotations shown below are redundant,because mypy can derive them from the type of the expression. Somany of the examples have a dual purpose: show how to write theannotation, and show the inferred types.
Variables¶
File = open('Hello.txt', 'a') # open in append mode file.write('Hello World again') file.close.
Python 3.6 introduced a syntax for annotating variables in PEP 526and we use it in most examples.
Built-in types¶
Functions¶
Python 3 supports an annotation syntax for function declarations.
When you’re puzzled or when things are complicated¶
Python 3 Cheat Sheet For Beginners
Standard “duck types”¶
In typical Python code, many functions that can take a list or a dictas an argument only need their argument to be somehow “list-like” or“dict-like”. A specific meaning of “list-like” or “dict-like” (orsomething-else-like) is called a “duck type”, and several duck typesthat are common in idiomatic Python are standardized.
You can even make your own duck types using Protocols and structural subtyping.
Classes¶
Python 3 Cheat Sheet
Coroutines and asyncio¶
See Typing async/await for the full detail on typing coroutines and asynchronous code.
Miscellaneous¶
Decorators¶
Decorator functions can be expressed via generics. SeeDeclaring decorators for more details.