如何计算字符串中的字符？ （蟒蛇） [英] How to count characters in a string? (python)

问题描述

# -*- coding:UTF-8 -*-

str= "Green tree"
scr= "e"

cstr= len(str)
n=0
a=0

while n < cstr:
    if str[n] == scr:
        print(len(scr))
    n=n+1

我必须在-str-字符串中计算 e，但是运行此脚本时，我会得到

I have to count "e" in -str- string, but when I run this script I get

1
1
1
1

而不是4。

出什么问题了？

推荐答案

首先，不要使用 str 作为变量名，它将掩盖内置名称。

First of all, don't use str as a variable name, it will mask the built-in name.

关于计数字符串中的字符，只需使用 str.count（） 方法：

As for counting characters in a string, just use the str.count() method:

>>> s = "Green tree"
>>> s.count("e")
4

如果您只是想了解为什么您当前的代码不起作用，您正在打印 1 四次，因为您会发现四个出现的'e'，并且当找到一个出现时，您正在打印 len（scr）始终为 1 。

If you are just interested in understanding why your current code doesn't work, you are printing 1 four times because you will find four occurrences of 'e', and when an occurrence is found you are printing len(scr) which is always 1.

代替打印 len（scr）在您的if块中，您应该增加一个计数器来跟踪找到的总发生次数，就像您设置了一个变量 a 您未使用的代码，因此为了使代码正常工作，对代码进行的最小更改如下（但是如上所述， str.count（ ）是一种更好的方法）：

Instead of printing len(scr) in your if block, you should be incrementing a counter that keeps track of the total number of occurrences found, it looks like you set up a variable a that you aren't using, so the smallest change to your code to get it to work would be the following (however as noted above, str.count() is a better approach):

str= "Green tree"
scr= "e"

cstr= len(str)
n=0
a=0

while n < cstr:
    if str[n] == scr:
        a+=1
    n=n+1
print(a)

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