python中的def是什么意思啊_在Python函数定义中-是什么意
思？
这些是PEP 3107中介绍的函数注释。具体来说，->标记返回函数注释。
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'}
注释是字典，因此您可以执⾏以下操作：>>> '{:,} {}'.format(kinetic_energy(20,3000),
kinetic_energy.__annotations__['return'])
'90,000,000.0 Joules'
您还可以使⽤python数据结构，⽽不仅仅是字符串：>>> 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'
value函数什么意思
>>> f.__annotations__['return']['docstring']
'Given mass and velocity returns kinetic energy in Joules'
或者，可以使⽤函数属性验证调⽤的值：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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