string.upper(< str>)和< str> .upper()不会执行 [英] string.upper(<str>) and <str>.upper() won't execute

问题描述

我有以下代码:

def test():
    fragment = ''
    fragment = raw_input('Enter input')
    while fragment not in string.ascii_letters:
        fragment = raw_input('Invalid character entered, try again: ')
    fragment.upper()
    print fragment*3

但是，当我运行它时，例如对于输入值p，fragment被打印为'ppp'-所有小写字母，即fragment.upper()行不运行.如果我用string.upper(fragment)替换该行(并在开始处添加 import string )，也会发生同样的事情.有人可以告诉我我在做什么错吗?

However when I run it, say for an input value of p, fragment gets printed as 'ppp' - all lower case, i.e. the fragment.upper() line does not run. The same thing happens if I replace that line with string.upper(fragment) (and adding import string at the beginning). Can someone tell me what I'm doing wrong?

推荐答案

字符串是不可变.因此，像str.upper()这样的函数将不会修改str而是返回一个新字符串.

Strings are immutable. So functions like str.upper() will not modify str but return a new string.

>>> name = "xyz"
>>> name.upper()
'XYZ'
>>> print name
xyz  # Notice that it's still in lower case.
>>> name_upper = name.upper()
>>> print name_upper
XYZ

因此，您需要执行new_variable = fragment.upper()而不是代码中的fragment.upper()，然后使用此new_variable.

So instead of fragment.upper() in your code, you need to do new_variable = fragment.upper()and then use this new_variable.

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