James Hartley wrote: > I have implemented the equivalent of "insert if unique" in Python & > SQLAlchemy to help with data normalization. However to help minimize the > number of preliminary SELECT statements needed, it helps to check types > through calls to isinstance() before getting to the salient code. > Unfortunately, the code begins to be cluttered with type-checking > minutiae. > > While researching this problem, I have found potential solutions like the > following: > > http://stackoverflow.com/questions/9305751/force-python-class-member-variable-to-be-specific-type > > ...but given that Python 3.5 has syntactically understands gradual typing, > I have wondered whether addition of this feature offers anything over use > of property() as described above. Toy examples have not revealed anything > useful on this front: > > $ cat example.py > #!/usr/bin/env python > > class Foobar(): > def __init__(self, value): > self.value = value > > def f(s: str) -> int: > print(s) > return 3.14 > > def main(): > i = f('foobar') > print(type(i)) > print('i = "{}"'.format(i)) > i = f(Foobar(3)) > print(type(i)) > print('i = "{}"'.format(i)) > > if __name__ == '__main__': > main() > $ python example.py > foobar > <class 'float'> > i = "3.14" > <__main__.Foobar object at 0x85b8aaac> > <class 'float'> > i = "3.14" > $ > > I understand that gradual typing may be useful with static analysis, but I > don't see that any type enforcement occurs by default at runtime. Am I > missing something here? Is there a better solution for type enforcement?
Quoting <https://www.python.org/dev/peps/pep-0484>: """ no type checking happens at runtime . Instead, the proposal assumes the existence of a separate off-line type checker which users can run over their source code voluntarily. Essentially, such a type checker acts as a very powerful linter """ You need an external tool http://mypy-lang.org/ to perform a type check: (mypylang)$ mypy example.py example.py: note: In function "f": example.py:9: error: Incompatible return value type (got "float", expected "int") (mypylang)$ _______________________________________________ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: https://mail.python.org/mailman/listinfo/tutor
