Python 3和静态类型是怎样使用的?

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我没有真正关注Python 3的开发,只是注意到了一些有趣的新语法变化:

def digits(x:'nonnegative number') -> "yields number's digits":
    # ...


'''Very simple enforcer of type annotations.

This toy super-decorator can decorate all functions in a given module that have 
annotations so that the type of input and output is enforced; an AssertionError is
raised on mismatch.

This module also has a test function func() which should fail and logging facility 
log which defaults to print. 

Since this is a test module, I cut corners by only checking *keyword* arguments.


import sys

log = print

def func(x:'int' = 0) -> 'str':
    '''An example function that fails type checking.'''
    return x

# For simplicity, I only do keyword args.
def check_type(*args):
    param, value, assert_type = args
    log('Checking {0} = {1} of {2}.'.format(*args))
    if not isinstance(value, assert_type):
        raise AssertionError(
            'Check failed - parameter {0} = {1} not {2}.'
    return value

def decorate_func(func):    
    def newf(*args, **kwargs):
        for k, v in kwargs.items():
            check_type(k, v, ann[k])
        return check_type('<return_value>', func(*args, **kwargs), ann['return'])

    ann = {k: eval(v) for k, v in func.__annotations__.items()}
    newf.__doc__ = func.__doc__
    newf.__type_checked = True
    return newf

def decorate_module(module = '__main__'):
    '''Enforces type from annotation for all functions in module.'''
    d = sys.modules[module].__dict__
    for k, f in d.items():
        if getattr(f, '__annotations__', {}) and not getattr(f, '__type_checked', False):
            log('Decorated {0!r}.'.format(f.__name__))
            d[k] = decorate_func(f)

if __name__ == '__main__':

    # This will raise AssertionError.
    func(x = 5)


height = 1.75 # Bob's height in meters.
length = len(sys.modules) # Number of modules imported by program.
area = height * length # What's that supposed to mean???