[Python-ideas] ideas for type hints for variable: beyond comments
ian.team.python at gmail.com
Tue Sep 1 12:24:15 CEST 2015
mypy currently inspects the comment on the line of first assignment for
the variables to be type hinted.
It is logical that at some time python language will add support to
allow these type hints to move from comments to the code as has happened
for 'def' signatures.
One logical syntax would be to move from
i = 1 # Infer type int for i
i:int = 1 # no comment needed, but does not look attractive
The first question that arises is 'is the type inference legal for the
additional uses. Having a 'second use' flagged by warning or error by
either an external typechecker or even the language itself could pick up
on accidental reuse of a name, but in practice accidentally creating a
new variable through a typo can be more common. In python today the
first use is the same as every other, so this change just does not feel
comfortable. The other question is 'what about globals and nonlocals?'.
Currently globals and nonlocals need a 'global' or 'nonlocal' statement
to allow assignment, but what if these values are not assigned in scope?
What if we allowed
Permitting a new keyword 'local' to me might bring far more symmetry
between different cases.
It would also allow type hinting to be collected near the function
definition and keep the type hinting clear of the main code.
Use of the 'local' keyword in the global namespace could indicate a
value not accessible in other namespaces.
Personally I would like to go even further and allow some syntax to
allow (or disable) flagging the use of new variables without type
hinting as possible typos
I have a syntax in mind, but the idea is the discussion point, not the
Possibly what is here already is too much of a change of direction to
consider for ideas already in progress?
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