IndexError：解析方法参数时元组索引超出范围答案

【问题标题】：IndexError: tuple index out of range when parsing method argumentsIndexError：解析方法参数时元组索引超出范围
【发布时间】：2017-05-28 16:06:07
【问题描述】：

我已经检查了this 问题，但在那里找不到答案。这是一个演示我的用例的简单示例：

def log(*args):
    message = str(args[0])
    arguments = tuple(args[1:])
    # message itself
    print(message)
    # arguments for str.format()0
    print(arguments)
    # shows that arguments have correct indexes
    for index, value in enumerate(arguments):
        print("{}: {}".format(index, value))
    # and amount of placeholders == amount of arguments
    print("Amount of placeholders: {}, Amount of variables: {}".format(message.count('{}'), len(arguments)))

    # But this still fails! Why?
    print(message.format(arguments))

log("First: {}, Second: {}, Third: {}, Fourth: {}", "asdasd", "ddsdd", "12312333", "fdfdf")

还有输出：

First: {}, Second: {}, Third: {}, Fourth: {}
('asdasd', 'ddsdd', '12312333', 'fdfdf')
0: asdasd
1: ddsdd
2: 12312333
3: fdfdf
Amount of placeholders: 4, Amount of variables: 4
Traceback (most recent call last):
  File "C:/Users/sbt-anikeev-ae/IdeaProjects/test-this-thing-on-python/test-this-thing.py", line 12, in <module>
    log("First: {}, Second: {}, Third: {}, Fourth: {}", "asdasd", "ddsdd", "12312333", "fdfdf")
  File "C:/Users/sbt-anikeev-ae/IdeaProjects/test-this-thing-on-python/test-this-thing.py", line 10, in log
    print(message.format(arguments))
IndexError: tuple index out of range

PS：我已经拒绝使用这种方法（包装str.format()），因为它似乎是多余的。但它仍然让我感到困惑，为什么这不能按预期工作？

【问题讨论】：

标签： python string-formatting

【解决方案1】：

您必须使用* 将元组解包为format 的实际参数：

print(message.format(*arguments))

否则，arguments 被视为格式的唯一参数（它适用于第一次出现的{}，通过将元组转换为字符串，但遇到第二次出现的{} 时会阻塞）

【讨论】：

【解决方案2】：

您需要传递参数而不是元组。这是通过使用'*arguments'来完成的。 Expanding tuples into arguments

def log(*args):
    message = str(args[0])
    arguments = tuple(args[1:])
    # message itself
    print(message)
    # arguments for str.format()0
    print(arguments)
    # shows that arguments have correct indexes
    for index, value in enumerate(arguments):
        print("{}: {}".format(index, value))
    # and amount of placeholders == amount of arguments
    print("Amount of placeholders: {}, Amount of variables: {}".format(message.count('{}'), len(arguments)))

    # But this still fails! Why?
    print(type(arguments))
    print(message.format(*arguments))

log("First: {}, Second: {}, Third: {}, Fourth: {}", "asdasd", "ddsdd", "12312333", "fdfdf")

【讨论】：

【解决方案3】：

试试这个

print(message.format(*arguments))

format 不需要元组

【讨论】：