Annotating namedtuples item types

[JukkaL]

There should be a way of annotating the item types of named tuples. Here is my suggested syntax:

X = namedtuple('X', ['a', 'b']) # type: (int, str)

The type of a would be int and the type of b would be str.

[mvitousek]

This reads to me more like an annotation for a normal tuple -- I would expect that something with type (int, str) would be a tuple, not a named tuple, and I would expect that any assignment with a # type: on it really does mean that the assignee has the type specified. What about having typing provide a typednamedtuple (or similar) that takes the expected types as part of its parameters, e.g.

X = typednamedtuple('X', {'a':int, 'b':int})

This would also help out tools like jython and reticulated that currently are unequipped to parse comment typings.

[gvanrossum]

The problem is that dicts are unordered, while namedtuple requires the
fields to be ordered.

On Thu, Nov 6, 2014 at 4:14 PM, Michael Vitousek notifications@github.com
wrote:

This reads to me more like an annotation for a normal tuple -- I would
expect that something with type (int, str) would be a tuple, not a named
tuple, and I would expect that any assignment with a # type: on it really
does mean that the assignee has the type specified. What about having
typing provide a typednamedtuple (or similar) that takes the expected
types as part of its parameters, e.g.

X = typednamedtuple('X', {'a':int, 'b':int})

This would also help out tools like jython and reticulated that currently
are unequipped to parse comment typings.

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#21 (comment).

--Guido van Rossum (python.org/~guido)

[mvitousek]

Ah, right, of course. The same principle could still work with

X = typednamedtuple('X', ['a', 'b'], [int, str])

perhaps.

[JukkaL]

Maybe we should call it NamedTuple, similar to List vs. list?

Another syntax idea:

X = NamedTuple('X', [('a', int), ('b', str)])

This syntax is arguably more readable if the tuple has many items, as it's obvious which types map to which items.

[gvanrossum]

+1 on both points.
On Nov 8, 2014 6:13 PM, "Jukka Lehtosalo" notifications@github.com wrote:

Maybe we should call it NamedTuple, similar to List vs. list?

Another syntax idea:

X = NamedTuple('X', [('a', int), ('b', str)])

This syntax is arguably more readable if the tuple has many items, as it's
obvious which types map to which items.

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#21 (comment).

[JukkaL]

I've started implementing my last idea (NamedTuple) for mypy. I don't have much experience with it yet, but it looks pretty reasonable so far.

[ambv]

Typing namedtuples is a good idea.
X = NamedTuple('X', [('a', int), ('b', str)]) is the obvious solution here but the syntax is punctuation heavy. Be sure to support the alternative namedtuple syntax that was X = namedtuple('x', 'a b'). Then you can just do X = NamedTuple('X', 'a:int, b:str').

[gvanrossum]

Jukka has just implemented this for mypy. See
https://github.com/JukkaL/typing/issues/7#issuecomment-68984316 .

(Hm, we have too many repos with issue trackers where we have these
discussions. Let's try to move discussions about what things should look
like to the typehinting repo.)

On Tue, Jan 6, 2015 at 11:58 PM, Łukasz Langa notifications@github.com
wrote:

Typing namedtuples is a good idea.
X = NamedTuple('X', [('a', int), ('b', str)]) is the obvious solution
here but the syntax is punctuation heavy. Be sure to support the
alternative namedtuple syntax that was X = namedtuple('x', 'a b'). Then
you can just do X = NamedTuple('X', 'a:int, b:str').

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Reply to this email directly or view it on GitHub
#21 (comment).

--Guido van Rossum (python.org/~guido)

[ambv]

Agreed to keep discussions in one place. Context-switching between the repos slows us down.

[gvanrossum]

This is also implemented in my typing.py.

[refi64]

I'm late to this discussion...but, wasn't there recently a discussion on making dicts in CPython ordered by default like PyPy does? If that were to happen, could the the dict-based syntax for namedtuples be supported?

[gvanrossum]

Yes, but that's a big if -- I don't know who's actually working on that. If dicts become ordered we can support that -- but even so, I'd like to support the list-of-tuples form for compatibility with Python 3.2-3.4.

[gvanrossum]

Closing, it's now also described in the PEP.

[gvanrossum]

Oops.