Type hints and chained assignment and multiple assignments

Question

I guess these two questions are related, so I'll post them together:

1.- Is it possible to put type hint in chained assignments?

These two attempts failed:

>>> def foo(a:int):
...     b: int = c:int = a
  File "<stdin>", line 2
    b: int = c:int = a
              ^
SyntaxError: invalid syntax
>>> def foo(a:int):
...     b = c:int = a
  File "<stdin>", line 2
    b = c:int = a
         ^
SyntaxError: invalid syntax

2.- Is it possible to put type hint in multiple assignments?

These were my attempts:

>>> from typing import Tuple
>>> def bar(a: Tuple[int]):
...     b: int, c:int = a
  File "<stdin>", line 2
    b: int, c:int = a
          ^
SyntaxError: invalid syntax
>>> def bar(a: Tuple[int]):
...     b, c:Tuple[int] = a
... 
  File "<stdin>", line 2
SyntaxError: only single target (not tuple) can be annotated
>>> def bar(a: Tuple[int]):
...     b, c:int = a
... 
  File "<stdin>", line 2
SyntaxError: only single target (not tuple) can be annotated

I am aware that in both cases the type is inferred from the type hint of a, but I have a long variable list (in the __init__ of a class) and I want to be extra-explicit.

I am using Python 3.6.8.

Hymanhymen

We really prefer one question per question. The second half is a duplicate of #52083439 which has some additional solutions in the answers. – Sycosis

Answer 1

1. As explicitly stated in PEP 526, section "Rejected/postponed proposals", annotations in chained assignments are not supported. Quoting the PEP:

   This has problems of ambiguity and readability similar to tuple unpacking, for example in:
   x: int = y = 1
z = w: int = 1
   it is ambiguous, what should the types of y and z be? Also the second line is difficult to parse.

2. For unpacking, per the same PEP, you should place bare annotations for your variables before the assignment. Example from the PEP:

   # Tuple unpacking with variable annotation syntax
   header: str
   kind: int
   body: Optional[List[str]]
   header, kind, body = message
   

Crore

This is very helpful, thank you. However, it is already four years from the question and answer. Have things changed or is the answer still the (only) correct way? Intuitively I would write, for example, a: int, b: str = func() for a function returning tuple[int, str]. But it does not work. – Mikamikado