As of May 2015, PEP 484 (Type Hints) has been formally accepted. The draft implementation is also available at github under ambv/typehinting.
In September 2015, Python 3.5 was released with support for Type Hints and includes a new typing module. This allows for the specification of types contained within collections. As of November 2015, JetBrains PyCharm 5.0 fully supports Python 3.5 to include Type Hints as illustrated below.
from typing import List
def do_something(l: List[str]):
for s in l:
s # str
Original Answer
As of Aug 2014, I have confirmed that it is not possible to use Python 3 type annotations to specify types within collections (ex: a list of strings).
The use of formatted docstrings such as reStructuredText or Sphinx are viable alternatives and supported by various IDEs.
It also appears that Guido is mulling over the idea of extending type annotations in the spirit of mypy: http://mail.python.org/pipermail/python-ideas/2014-August/028618.html
Answer from Eric W. on Stack OverflowAs of May 2015, PEP 484 (Type Hints) has been formally accepted. The draft implementation is also available at github under ambv/typehinting.
In September 2015, Python 3.5 was released with support for Type Hints and includes a new typing module. This allows for the specification of types contained within collections. As of November 2015, JetBrains PyCharm 5.0 fully supports Python 3.5 to include Type Hints as illustrated below.
from typing import List
def do_something(l: List[str]):
for s in l:
s # str
Original Answer
As of Aug 2014, I have confirmed that it is not possible to use Python 3 type annotations to specify types within collections (ex: a list of strings).
The use of formatted docstrings such as reStructuredText or Sphinx are viable alternatives and supported by various IDEs.
It also appears that Guido is mulling over the idea of extending type annotations in the spirit of mypy: http://mail.python.org/pipermail/python-ideas/2014-August/028618.html
As of Python 3.9, builtin types are generic with respect to type annotations (see PEP 585). This allows to directly specify the type of elements:
def my_func(l: list[int]):
pass
This also extends to most other container types of the standard library, for example collections.deque or collections.abc.Mapping.
Various tools may support this syntax earlier than Python 3.9. When annotations are not inspected at runtime, the syntax is valid using quoting or __future__.annotations.
# quoted
def my_func(l: 'list[int]'):
pass
# postponed evaluation of annotation
from __future__ import annotations
def my_func(l: list[int]):
pass
As a consequence of PEP 585, most helpers in typing corresponding to standard library types are deprecated, such as typing.List, typing.Deque or typing.Mapping. They should only be used if compatibility with Python versions prior to 3.9 is required.
Videos
I like to refactor my Advent of Code solutions over time to see where I could have done things differently, especially as I pick up new ideas.
2021's day 8 input has many lines of input that look like this:
acedgfb cdfbe gcdfa fbcad dab cefabd cdfgeb eafb cagedb ab | cdfeb fcadb cdfeb cdbaf
Two lists of space separated groups of letters which are, in turn, separated by "|".
My code to get the input looks like this:
entries = []
with open("input/input_08.txt") as file:
for signal, output in (ln.strip().split(" | ") for ln in file):
entries.append([signal.split(), output.split()])How should I type hint entries? I'd like to do something like:
entries: list[list[str],list[str]] = []
But, that doesn't work. When I look at the mypy docs and cheatsheet or the Python docs and hinting PEPs, I can't really see how I should be hinting a structure like this. Is there a way to do it? Should I be using a different structure?