我正在查看python 3.3 grammar,并在其中注意到这一行:
funcdef: 'def' NAME parameters ['->' test] ':' suite
这意味着 - >在定义函数时是一个有效的符号,但我无法在网上找到它的内容,而且据我所知,它被忽略了。例如,我可以编写执行此操作的代码:
def a() -> True: pass
或
def a() -> 5 == 3:
return 8
都是有效的陈述,但似乎没有做任何事情。
有人能告诉我python中的->
语法吗?
答案 0 :(得分:0)
这些是PEP 3107中涵盖的功能注释。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,因此您可以这样做:
>>> '{:,} {}'.format(kenetic_energy(20,3000),
kenetic_energy.__annotations__['return'])
'90,000,000.0 Joules'
或者,您可以使用函数属性来验证调用值:
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)
打印
>>> f(2,2)
AssertionError: x==2; Test: _between: must be between 3 and 10
>>> f(3,2.1)
AssertionError: y==2.1; Test: <lambda>