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默认参数后跟可变长度参数(Python)

parameter-passing arguments python-3.x python

-1

arshovon · 技术社区 · 7 年前

我有一个函数,它接受一个位置参数、一个默认参数、可变长度非关键字参数和可变长度关键字参数。该函数如下所示:

def set_football_team(name,
                     coach = '',
                     *players, **formations):
    print("Team: "+name)
    print("Coach: "+coach)
    for i, player in enumerate(players):
        print("Player "+str(i+1)+": "+player)
    for position, positional_players in formations.items():
        positional_players = ", ".join(positional_players)
        print(position+": "+positional_players)

当所有参数都被传递时,它工作正常。

name = "Real Madrid"
coach = "Zinedine Zidane"
players = ["Keylor Navas", "K. Casilla",
           "Sergio Ramos", "Varane", "Marcelo"]

formations = {"Goalkeeper": players[:2],
              "Defender": players[2:]}

set_football_team(name, coach, *players, **formations)

Output
==============================================
Team: Real Madrid
Coach: Zinedine  Zidane
Player 1: Keylor Navas
Player 2: K. Casilla
Player 3: Sergio Ramos
Player 4: Varane
Player 5: Marcelo
Goalkeeper: Keylor Navas, K. Casilla
Defender: Sergio Ramos, Varane, Marcelo

但当我跳过传球时 coach 它显示了意外的输出,即使我设置了 教练 到参数中的空字符串:

name = "Real Madrid"
players = ["Keylor Navas", "K. Casilla",
           "Sergio Ramos", "Varane", "Marcelo"]

formations = {"Goalkeeper": players[:2],
              "Defender": players[2:]}

set_football_team(name, *players, **formations)

Output
==============================================    
Team: Real Madrid
Coach: Keylor Navas
Player 1: K. Casilla
Player 2: Sergio Ramos
Player 3: Varane
Player 4: Marcelo
Goalkeeper: Keylor Navas, K. Casilla
Defender: Sergio Ramos, Varane, Marcelo

我知道函数参数的顺序:

positional argument > default argument > variable length non keyword arguments > variable length keyword arguments

上述行为的原因是什么?我错过了什么?

我如何克服这个问题?

1 回复 | 直到 3 年前

dev2qa 7 年前

set_football_team(name, coach, *players, **formations)

如上所述调用函数时,coach作为参数传递,coach将被分配在函数set\u football\u team的参数中传递的值。

set_football_team(name,*players, **formations)

当没有显式传递coach参数时,如上所述调用该函数时,coach主要被分配给*players的第一个值,players的剩余值被传递给players,这就是为什么您注意到players中只有4个players,而列表中的第0个元素被分配给coach。