這些是PEP 3107中介紹的函數注釋。具體來說，->標記返回函數注釋。

示例：>>> def kinetic_energy(m:'in KG', v:'in M/S')->'Joules':

... return 1/2*m*v**2

...

>>> kinetic_energy.__annotations__

{'return': 'Joules', 'v': 'in M/S', 'm': 'in KG'}

注釋是字典，因此您可以執行以下操作：>>> '{:,} {}'.format(kinetic_energy(20,3000),

kinetic_energy.__annotations__['return'])

'90,000,000.0 Joules'

您還可以使用python數據結構，而不僅僅是字符串：>>> rd={'type':float,'units':'Joules','docstring':'Given mass and velocity returns kinetic energy in Joules'}

>>> def f()->rd:

... pass

>>> f.__annotations__['return']['type']

>>> f.__annotations__['return']['units']

'Joules'

>>> f.__annotations__['return']['docstring']

'Given mass and velocity returns kinetic energy in Joules'

或者，可以使用函數屬性驗證調用的值：def validate(func, locals):

for var, test in func.__annotations__.items():

value = locals[var]

try:

pr=test.__name__+': '+test.__docstring__

except AttributeError:

pr=test.__name__

msg = '{}=={}; Test: {}'.format(var, value, pr)

assert test(value), msg

def between(lo, hi):

def _between(x):

return lo <= x <= hi

_between.__docstring__='must be between {} and {}'.format(lo,hi)

return _between

def f(x: between(3,10), y:lambda _y: isinstance(_y,int)):

validate(f, locals())

print(x,y)

印刷品>>> f(2,2)

AssertionError: x==2; Test: _between: must be between 3 and 10

>>> f(3,2.1)

AssertionError: y==2.1; Test:

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