问题
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").
My function:
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
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))
Error:
NameError: name 'myByteArray' is not defined
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?
In C++ this would be easy, as argument types are specified when you write functions.
回答1:
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
回答2:
At the time of passing the parameters, the parameters are not initialised
>>> def a(b=1,c=b):
... print(c,b)
...
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
NameError: name 'b' is not defined
so you need to send len of myByteArray as another variable.
So what you could do is,
def circularFind(myByteArray, searchVal, start=0, end=-1):
if end == -1:
end = len(myByteArray)
#reset of code here.
来源:https://stackoverflow.com/questions/38986341/python-nameerror-name-is-not-defined-related-to-having-default-input-argument