typechecking python NamedTuple in both python 2 and 3

Question

I have a Python code that works with both python2 and python3 and uses mypy. I managed to have my namedtuples typechecked with the following really convoluted method:

try:
    from typing import TYPE_CHECKING
except ImportError:
    TYPE_CHECKING = False

if TYPE_CHECKING:
    from typing import NamedTuple
    Foo = NamedTuple("Foo", [("foo", int)])
else:
    from collections import namedtuple
    Foo = namedtuple("Foo", ["foo"])

correct = Foo(foo= 1)
incorrect = Foo(foo= "bla") # error: Argument 1 to "Foo" has incompatible type "str"; expected "int"

Note: using something like this to define fields only once does not work:

foo_typed_fields = [("foo", int)]
foo_fields = [f[0] for f in foo_typed_fields]

Question: Is there a simpler way to do this ?

Michael0x2a · Accepted Answer · 2019-08-21 16:48:48Z

1

Yes -- install the official typing module backport for Python 2 (e.g. pip install typing or pip2 install typing), then just do the following:

from typing import NamedTuple

Foo = NamedTuple("Foo", [("foo", int)])

answered Aug 21, 2019 at 16:48

Michael0x2a

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