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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