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Type variable substitution in type instances #156
Description
[In http://bugs.python.org/issue25087 Stefan Krah wrote:]
If a type scheme is instantiated, should the type variables in the
class body be substituted? This is an example (typed by hand on
a locked down Windows machine, may contain errors):
alpha = TypeVar('alpha')
beta = TypeVar('beta')
class ABTuple(Generic[alpha, beta]):
def __init__(self, a : alpha, b : beta):
self.value = (a, b)
get_type_hints(ABTuple.__init__)
==> {'b': ~beta, 'a': ~alpha}
IntIntTuple = ABTuple[int, int]
IntIntTuple
==> __main__.ABTuple[int, int]
get_type_hints(IntIntTuple.__init__)
{'b': ~beta, 'a': ~alpha}
^^^^^^ ^^^^^^
Since the type has been specialized, these should ideally be 'int'.
Activity
gvanrossum commentedon Sep 13, 2015
Unfortunately this info is hard to retrieve at run time. The object returned by the expression
IntIntTuple.__init__is a plain function -- it only knows that it was defined inABTuple. You could write a custom function though that is passed in separately theIntIntTupleclass and the string'__init__'-- it can then do the expansion for you after introspection ofIntIntTuple. (See also #136 (comment) and further comments).Refactor Union, Tuple, and Callable (#308)