我有一个更简单的解决方案，使用for循环来查找字符串中的给定子字符串。假设我们有两个字符串变量，

main_string = "lullaby"
match_string = "ll"

如果要检查主字符串中是否存在给定的匹配字符串，可以执行以下操作：，

match_string_len = len(match_string)
for index,value in enumerate(main_string):
    sub_string = main_string[index:match_string_len+index]
    if sub_string == match_string:
       print("match string found in main string")

str1='There you are'
>>> str1[:]
'There you are'

>>> str1[1:]
'here you are'

#To print alternate characters skipping one element in between

>>> str1[::2]
'Teeyuae'

#To print last element of last two elements
>>> str1[:-2:-1]
'e'

#Similarly
>>> str1[:-2:-1]
'e'


#Using slice datatype

>>> str1='There you are'
>>> s1=slice(2,6)
>>> str1[s1]
'ere '

实现这一点的常见方法是通过字符串切片。

MyString[a:b]提供了从索引a到（b-1）的子字符串。

text = "StackOverflow"
#using python slicing, you can get different subsets of the above string

#reverse of the string
text[::-1] # 'wolfrevOkcatS' 

#fist five characters
text[:5] # Stack'

#last five characters
text[-5:] # 'rflow'

#3rd character to the fifth character
text[2:5] # 'rflow'

#characters at even positions
text[1::2] # 'tcOefo'

为了完整性，其他人没有提到过。数组切片的第三个参数是一个步骤。因此，反转字符串非常简单：

some_string[::-1]

或者选择其他字符：

"H-e-l-l-o- -W-o-r-l-d"[::2] # outputs "Hello World"

在字符串中前后移动的能力与从开始或结束排列切片的能力保持一致。

>>> x = "Hello World!"
>>> x[2:]
'llo World!'
>>> x[:2]
'He'
>>> x[:-2]
'Hello Worl'
>>> x[-2:]
'd!'
>>> x[2:-2]
'llo Worl'

Python将这一概念称为“切片”，它不仅仅适用于字符串。请在此处查看全面介绍。