python - 默认参数不起作用

我在Python代码中遇到以下问题。

错误是：

Traceback (most recent call last): File "cmd.py", line 16, in <module>
    func(b="{cmd} is entered ...") # Error here
File "cmd.py", line 5, in func
    exceptMsg = b.format(errStr=errStr, debugStr=debugStr)
KeyError: 'cmd'

代码：

import re

def func(errStr = "A string", b = "{errStr}\n{debugStr}"):
    debugStr = "Debug string"
    exceptMsg = b.format(errStr=errStr, debugStr=debugStr)
    raise ValueError(exceptMsg)

try:
    '''
    Case 1: If user invokes func() like below, error produced.
    Possible explanation: Paramter b of func() is looking keyword
    'errStr' further down in func() body, but I am passing it keyword
    'cmd' instead. What to change to make the code work?
    '''
    #cmd = "A crazy string"             # Comment, make code pass
    #func(b="{cmd} is entered ...")     # Error here

    # Case 2: If user invokes func() like below, OK.
    errStr = "A crazy string"
    func(b="{errStr} is entered")

except ValueError as e:
    err_msg_match = re.search('A string is entered:', e.message)
    print "Exception discovered and caught!"

1）如果函数接口func（）被保留，要更改哪些代码？

2）如果必须修改功能接口，如何进行干净的代码更改？

最佳答案

b.format(errStr=errStr, debugStr=debugStr)仅传递errStr和debugStr来替换占位符。如果b包含任何其他占位符变量，它将失败。

你有：

b = "{cmd} is entered ..."

没有匹配项{cmd}

如果要将cmd传递给func，则可以使用keyword arguments进行操作：

def func(errStr = "A string", b = "{errStr}\n{debugStr}", **kwargs):
    debugStr = "Debug string"
    exceptMsg = b.format(errStr=errStr, debugStr=debugStr, **kwargs)
    raise ValueError(exceptMsg)

并用作：

func(b="{cmd} is entered ...", cmd="A crazy string")