Python NameError:未定义名称(与具有默认输入参数类型有关) [英] Python NameError: name is not defined (related to having default input argument types)

问题描述

我有一个问题，我在我声明的函数的输入参数中调用 len(myByteArray).我希望这是一个默认参数，但 Python 似乎不喜欢它.myByteArray 是 bytearray 类型.请参阅此处有关 bytearray 的文档.我正在访问其内置的 find 函数，此处记录(参见bytes.find").

I have a problem with the fact that I am calling len(myByteArray) in the input arguments to a function I am declaring. I'd like that to be a default argument, but Python doesn't seem to like it. myByteArray is of type bytearray. See documentation on bytearray here. I am accessing its built-in find function, documented here (see "bytes.find").

我的功能:

def circularFind(myByteArray, searchVal, start=0, end=len(myByteArray)):
    """
    Return the first-encountered index in bytearray where searchVal 
    is found, searching to the right, in incrementing-index order, and
    wrapping over the top and back to the beginning if index end < 
    index start
    """
    if (end >= start):
        return myByteArray.find(searchVal, start, end)
    else: #end < start, so search to highest index in bytearray, and then wrap around and search to "end" if nothing was found 
        index = myByteArray.find(searchVal, start, len(myByteArray))
        if (index == -1):
            #if searchVal not found yet, wrap around and keep searching 
            index = myByteArray.find(searchVal, 0, end)
        return index 

尝试使用上述函数的示例:

Examples to attempt to use the function above:

#-------------------------------------------------------------------
#EXAMPLES:
#-------------------------------------------------------------------
#Only executute this block of code if running this module directly,
#*not* if importing it
#-see here: http://effbot.org/pyfaq/tutor-what-is-if-name-main-for.htm
if __name__ == "__main__": #if running this module as a stand-alone program
    import random
    random.seed(0)

    bytes = bytearray(100)
    for i in range(len(bytes)):
        bytes[i] = int(random.random()*256)

    print(list(bytes)); print();

    print('built-in method:')
    print(bytes.find(255))
    print(bytes.find(2,10,97))
    print(bytes.find(5,97,4))

    print('\ncircularFind:')
    print(circularFind(bytes,255))
    print(circularFind(bytes,2,10,97))
    print(circularFind(bytes,5,97,4))

错误:

NameError: name 'myByteArray' 未定义

NameError: name 'myByteArray' is not defined

如果我只是删除我的默认参数(=0 和 =len(myByteArray))，但是，它工作正常.但是......我真的想要那些默认参数，以便 start 和 end 参数是可选的.我该怎么办?

If I just remove my default arguments (=0 and =len(myByteArray)), however, it works fine. But...I really want those default arguments there so that the start and end arguments are optional. What do I do?

在 C++ 中，这很容易，因为在编写函数时会指定参数类型.

In C++ this would be easy, as argument types are specified when you write functions.

推荐答案

Python 默认参数在定义函数时进行计算.相反，您想要这样的东西:

Python default arguments are evaluated when the function is defined. Rather, you want something like this:

def circularFind(myByteArray, searchVal, start=0, end=None):
    """
    Return the first-encountered index in bytearray where searchVal 
    is found, searching to the right, in incrementing-index order, and
    wrapping over the top and back to the beginning if index end < 
    index start
    """
    if end is None:
        end = len(myByteArray)
    # continue doing what you were doing

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