为什么我不能使用一个步骤来更改Python列表中的项目？

Question

So I am still in the beginning stages of learning Python--and coding as a whole for that matter.

My question is why can I not change items in a Python list using a step, like this:

def myfunc2(string):
    new = list(string)
    new[0::2] = new[0::2].upper()
    new[1::2] = new[1::2].lower()

    return '' .join(new)

 myfunc2('HelloWorld')

I want to make every other letter upper and lower case, starting at index 0.

I had already seen a solution posted by another user, and although this other solution worked I had trouble understanding the code. So, in my curiosity I tried to work out the logic myself and came up with the above code.

Why is this not working?

Answer 1

new[0::2] returns a list, which does not have an upper method . Same goes for new[1::2] and lower .

You can achieve your goal with map :

def myfunc2(string):
    new = list(string)
    new[0::2] = map(str.upper, new[0::2])
    new[1::2] = map(str.lower, new[1::2])
    return '' .join(new)

print(myfunc2('HelloWorld'))
# HeLlOwOrLd