Python函数修改字符串 [英] Python function to modify string

问题描述

有一次我被要求创建一个函数，给定一个字符串，从字符串中删除几个字符.

是否可以在 Python 中执行此操作?

这可以用于列表，例如:

def poplist(l):l.pop()l1 = ['a', 'b', 'c', 'd']弹出列表(l1)打印 l1>>>['a', 'b', 'c']

我想要的是为字符串做这个函数.我能想到的唯一方法是将字符串转换为列表，删除字符，然后将其连接回字符串.但那时我将不得不返回结果.例如:

def 弹出字符串:副本 = 列表副本.pop()s = ''.join(复制)s1 = 'abcd'弹出字符串(s1)打印 s1>>>'A B C D'

我明白为什么这个功能不起作用.问题更多的是是否可以在 Python 中执行此操作?如果是，我可以不复制字符串吗?

解决方案

字符串不可变，这意味着你不能改变str对象.您当然可以构造一个新字符串，该字符串是对旧字符串的一些修改.但是你不能因此改变代码中的 s 对象.

一种解决方法可能是使用容器:

类容器:def __init__(self,data):self.data = 数据

然后 popstring 被赋予一个包含，它检查容器，并将其他东西放入其中:

def 弹出字符串(容器):容器.数据 = 容器.数据[:-1]s1 = 容器('abcd')弹出字符串(s1)

但同样:您没有更改字符串对象本身，您只是将一个新字符串放入容器中.

您不能在 Python 中执行按引用调用，所以你不能调用一个函数:

foo(x)

然后修改变量x:x的引用被复制，所以你不能修改变量x本身.>

I was asked once to create a function that given a string, remove a few characters from the string.

Is it possible to do this in Python?

This can be done for lists, for example:

def poplist(l):
    l.pop()

l1 = ['a', 'b', 'c', 'd']

poplist(l1)
print l1
>>> ['a', 'b', 'c']

What I want is to do this function for strings. The only way I can think of doing this is to convert the string to a list, remove the characters and then join it back to a string. But then I would have to return the result. For example:

def popstring(s):
    copys = list(s)
    copys.pop()
    s = ''.join(copys)

s1 = 'abcd'

popstring(s1)

print s1
>>> 'abcd'

I understand why this function doesn't work. The question is more if it is possible to do this in Python or not? If it is, can I do it without copying the string?

解决方案

Strings are immutable, that means you can not alter the str object. You can of course construct a new string that is some modification of the old string. But you can thus not alter the s object in your code.

A workaround could be to use a container:

class Container:

    def __init__(self,data):
        self.data = data

And then the popstring thus is given a contain, it inspect the container, and puts something else into it:

def popstring(container):
    container.data = container.data[:-1]

s1 = Container('abcd')
popstring(s1)

But again: you did not change the string object itself, you only have put a new string into the container.

You can not perform call by reference in Python, so you can not call a function:

foo(x)

and then alter the variable x: the reference of x is copied, so you can not alter the variable x itself.

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