1.编写一个程序来检查给定的密钥是否可用：

txt = "i love many fruits, apple is my favorite fruit"
key = 'fruit'
l = len(key)
start = 0 
end = l
while end<=len(txt):
    if txt[start:end] == key:
        print('contains', key)
        break
    start+=1
    end+=1
else:
    print('not contains')

contains fruit

2.编写一个程序来查找给定的关键位置：

find() 返回找到它的位置。

txt = "python is my favourite language"
key = 'python'
l = len(key)
start = 0 
end = l
while end<=len(txt):
    if txt[start:end] == key:
        print('contains', key)
        print(start,end-1)
        break
    start+=1
    end+=1
else:
    print('not contains')

contains python
0 5

3.编写程序检查以指定键开头的单词：

startswith() 检查字符串是否以指定值开头。

txt = "python is my favourite language"
key = 'python'
l = len(key)
start = 0 
end = l
while end<=len(txt):
    if txt[start:end] == key:
        if start==0:
            print("starts with", key)
        break
    start+=1
    end+=1
else:
    print('not contains')

starts with python

检查以指定键开头的单词的另一种方法：

txt = "apples are good, apple is my favorite fruit"
key = 'apple'
l = len(key) 
if txt[0:l]==key:
    print('starts with',key)

starts with apple

4.编写程序检查以指定键结尾的单词：

endswith() 检查字符串是否以指定值结尾。

txt = "my favourite language is python"
key = 'python'
l = len(key)
start = 0 
end = l
while end<=len(txt):
    if txt[start:end] == key:
        if end==len(txt):
            print("ends with", key)
        break
    start+=1
    end+=1
else:
    print('not contains')

ends with python

检查单词以指定键结尾的另一种方法：

txt = "apples are good, apple is my favorite fruit"
key = 'fruit'
l = len(key) 
if txt[-l:]==key:
    print('ends with',key)

ends with fruit

5.编写一个程序来检查给定的单词是否为字母：

isalpha() 检查字符串中的所有字符都是字母。

alpha = 'abcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyz'
word = 'abcdefgh'
for letter in word:
    if letter not in alpha:
        print('not all are alphabets')
        break
else:
    print('all are alphabets')

all are alphabets

6.编写一个程序来检查给定的单词是否为alnum：

isalnum() 检查字符串中的所有字符都是字母数字。

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alpha = '0123456789abcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyz'
word = 'pritha017@gmail.com'
for letter in word:
    if letter not in alpha:
        print('not all are alphabets and numbers')
        break
else:
    print('all are alphabets and numbers')

not all are alphabets and numbers

7.编写一个程序来检查给定的单词是否小写：

islower() 检查字符串中的所有字符均为小写。

alpha = 'abcdefghijklmnopqrstuvwxyz'
word = 'lakshmipritha'
for letter in word:
    if letter not in alpha:
        print('not all are lowercase alphabets')
        break
else:
    print('all are lowercase alphabets')

all are lowercase alphabets

8.编写一个程序来检查给定的单词是否大写：

isupper() 检查字符串中的所有字符均为大写。

alpha = 'abcdefghijklmnopqrstuvwxyz'
word = 'lakshmipritha'
for letter in word:
    if letter not in alpha:
        print('not all are uppercase alphabets')
        break
else:
    print('all are uppercase alphabets')

all are uppercase alphabets

9.编写一个程序来检查空间是否可用：

isspace() 检查文本中的空格。

word = '        '
for letter in word:
    if letter != ' ':
        print("not all are spaces")
        break
else:
    print('all are spaces')

all are spaces

任务：

1.编写一个将大写字母转换为小写字母的程序：

lower() 将字符串转换为小写。

txt = "hello, and welcome to my world!"
for letter in txt:
    if letter>='a' and letter<'z':
        letter = ord(letter)+32
        letter = chr(letter)
    print(letter,end='')

hello, and welcome to my world!

2.编写一个将小写字母转换为大写字母的程序：

upper() 将字符串转换为大写。

txt = "hello, and welcome to my world!"
for letter in txt:
    if letter>='a' and letter<'z':
        letter = ord(letter)-32
        letter = chr(letter)
    print(letter,end='')

hello, and welcome to my world!

3.编写一个程序来检查给定的字符串标题是否：

istitle() 检查字符串是否遵循标题规则。