📄 Parent resource: My general Python notes

Resources

• One page cheatsheet
• https://github.com/microsoft/pyright/blob/main/docs/type-concepts.md
• Official PEPs
  • PEP 484 – Type Hints
  • PEP 526 – Syntax for Variable Annotations
• PlainEnglish Python: Python for TypeScript Developers
• My docs: Using Python Type-Checking Features in VSCode
• Benita: Exhaustiveness Checking with Mypy

Miscellaneous Questions and TypeScript Equivalents

• Null or undefined types?
  • Python uses None instead of Null or Undefined.
  • Typing a possibly unset variable?
    • Although you can use possible_string: Union[None, other_type] to represent the type of None | other_type, a shorter way is with Optional[other_type]
  • Checking for None?
    • if my_var is None or even just if not my_var works for checking if variable == None, but not for checking if a variable exists period (this will throw an exception is variable is not defined)
• Equivalent to TS ReturnType<T>?
  • Does not exist - see issue #769
• Equivalent to TS typeof {MY_VAR}?
  • Nope, same as above
• Equivalent to @ts-ignore?
  • # type: ignore
• Equivalent to TS assertions?
  • Most efficient: myVar as myType -> typing.cast(my_type, my_var)
  • Less efficient: Using assert
  • https://stackoverflow.com/a/57931741/11447682

Troubleshooting

A word of warning; stubs can (and often are) shipped separately from the actual library; for example, VSCode's pylance extension provides out-of-the-box type stubs for Django, but these might not match the actual version of Django you happen to have installed in your project!

• Intellisense isn't kicking in when adding elements in an array, dict, etc.
  • Try adding a comma / separator before actually writing out the element. For some reason in VSCode, it won't work unless you do this when adding elements to a list.