你所不知道的Python | 函数参数的演进之路

1def add_record(date, amount):
2    print('date:', date, 'amount:', amount)

1add_record('2018-07-06', 10)  # 输出date: 2018-07-06 amount: 10
2add_record(10, '2018-07-06')  # 输出date: 10 amount: 2018-07-06

1add_record(amount=10, date='2018-07-06')  # 虽然参数顺序反了，但是使用了关键字调用，所以依然输出date: 2018-07-06 amount: 10

1class Person(object):
2    def __init__(self, name, age,  gender, height, weight):
3        self._name = name
4        self._age = age
5        self._gender = gender
6        self._height = height
7        self._weight = weight

1Person('Wendy', 24, 'female', 160, 48)
2Person('John', age=27, gender='male', height=170, weight=52)

 1class Person(object):
 2        # 参数中的星号作为关键字参数和仅限关键字参数的分割
 3    def __init__(self, name, *, age='22', gender='female', height=160, weight=50):
 4        self._name = name
 5        self._age = age
 6        self._gender = gender
 7        self._height = height
 8        self._weight = weight
 9
10Person('Wendy', 24, 'female', 160, 48)  # 报错，age以后参数不允许位置调用
11Person('John', age=27, gender='male', height=170, weight=52)  # 正常执行

1def add_record(date, amount=0):
2    print('date:', date, 'amount:', amount)
3
4add_record('2018-07-06')  # 输出date: 2018-07-06 amount: 0

1add_record('2018-07-06', 10)  # 通过位置指定参数
2add_record('2018-07-06', amount=10)  # 通过位置指定参数
3add_record(amount=10, '2018-07-06')  # 报错，默认参数必须在必选参数后面

1def print_args(*args):
2    print(args)
3
4print_args(1, 2, 3, 4, 5)  # 输出元组(1, 2, 3, 4, 5)
5
6a = [1, 2, 3, 4, 5]
7print_args(a)  # 直接传入时，列表a会被当作一个元素，所以输出([1, 2, 3, 4, 5],)
8print_args(*a)  # 在传参时加星号可以将可迭代参数解包，所以列表a中每一个元素都被当作一个参数传入，输出(1, 2, 3, 4, 5)

1def print_kwargs(**kw_args):
2    print(kw_args)
3
4a = {'a': 1, 'b': 2, 'c': 3, 'd': 4, 'e': 5}
5print_kwargs(**a)  # 使用关键字可变参数时， {'a': 1, 'c': 3, 'b': 2, 'e': 5, 'd': 4}

1def create_person(name: str, age: int, gender: str = 'female', height: int = 160)  -> bool:
2    return True

1Person(name=123, age='John')  # 并不会报错