[issue25087] Type variable substitution in type instances

[Stefan Krah]

New submission from Stefan Krah:

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'.

----------
components: Interpreter Core
messages: 250565
nosy: gvanrossum, skrah
priority: normal
severity: normal
status: open
title: Type variable substitution in type instances
type: behavior
versions: Python 3.5

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Python tracker <report at bugs.python.org>
<http://bugs.python.org/issue25087>
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