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  1. import functools
  2.  
  3. ##
  4.  
  5. def typecheck(f):
  6.     def do_typecheck(name, arg):
  7.         trait = f.__annotations__.get(name, None)
  8.         if trait and not trait.is_satisfied(arg):
  9.             raise RuntimeError("{} is {} which does not satisfy trait {}".format(name, type(arg).__name__, trait.name))
  10.  
  11.     @functools.wraps(f)
  12.     def wrapper(*args, **kwargs):
  13.         for i, arg in enumerate(args[:f.__code__.co_nlocals]):
  14.             do_typecheck(f.__code__.co_varnames[i], arg)
  15.         for name, arg in kwargs.items():
  16.             do_typecheck(name, arg)
  17.  
  18.         result = f(*args, **kwargs)
  19.  
  20.         do_typecheck('return', result)
  21.         return result
  22.  
  23.     return wrapper
  24.  
  25. ##
  26.  
  27. class Trait:
  28.     def __init__(self, name, methods=None):
  29.         self.name = name
  30.         self.methods = [] if methods is None else methods
  31.  
  32.     def is_satisfied(self, value):
  33.         return all(hasattr(value, method) for method in self.methods)
  34.  
  35. num = Trait("num", ["__add__", "__sub__", "__mul__", "__truediv__"])
  36.  
  37. ##
  38.  
  39. @typecheck
  40. def gcd(a: num, b: num) -> num:
  41.     #Obviously, not the GCD
  42.     return a / b
  43.  
  44. try:
  45.     gcd(5, 6)
  46.     gcd(5, "hello")
  47.  
  48. except RuntimeError as e:
  49.     print(str(e))
Success #stdin #stdout 0.03s 9072KB
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Standard input is empty
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b is str which does not satisfy trait num
https://ideone.com/9uCEV1
language:
Python 3 (python  3.9.5)
created:
9 years ago
visibility:
public

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