python之字符串

创建字符串

s = "Hello, World!"

常用字符串操作

1. 获取字符串长度

length = len(s)
print(length)  # 输出: 13

2. 字符串拼接

s1 = "Hello"
s2 = "World"
s3 = s1 + ", " + s2 + "!"
print(s3)  # 输出: Hello, World!

3. 重复字符串

s = "Hello"
s_repeated = s * 3
print(s_repeated)  # 输出: HelloHelloHello

4. 字符串格式化

name = "Alice"
age = 30
formatted_string = f"My name is {name} and I am {age} years old."
print(formatted_string)  # 输出: My name is Alice and I am 30 years old.

5. 字符串分割

s = "Hello, World!"
parts = s.split(", ")
print(parts)  # 输出: ['Hello', 'World!']

6. 字符串连接

words = ["Hello", "World"]
joined_string = " ".join(words)
print(joined_string)  # 输出: Hello World

7. 字符串替换

s = "Hello, World!"
new_s = s.replace("World", "Python")
print(new_s)  # 输出: Hello, Python!

8. 字符串查找

s = "Hello, World!"
index = s.find("World")
print(index)  # 输出: 7

9. 字符串大小写转换

s = "Hello, World!"
print(s.upper())  # 输出: HELLO, WORLD!
print(s.lower())  # 输出: hello, world!
print(s.capitalize())  # 输出: Hello, world!
print(s.title())  # 输出: Hello, World!

10. 去除空白字符

s = "  Hello, World!  "
print(s.strip())  # 输出: Hello, World!
print(s.lstrip())  # 输出: Hello, World!  
print(s.rstrip())  # 输出:   Hello, World!

子字符串的用法

1. 获取子字符串

s = "Hello, World!"
sub_s = s[7:12]
print(sub_s)  # 输出: World

2. 检查子字符串

s = "Hello, World!"
print("World" in s)  # 输出: True
print("Python" in s)  # 输出: False

3. 子字符串计数

s = "Hello, World! Hello, Python!"
count = s.count("Hello")
print(count)  # 输出: 2

4. 子字符串索引

s = "Hello, World!"
index = s.index("World")
print(index)  # 输出: 7# 如果子字符串不存在，会抛出 ValueError
try:index = s.index("Python")
except ValueError:print("Substring not found")

5. 子字符串切片

s = "Hello, World!"
sub_s = s[7:]  # 从索引 7 开始到结尾
print(sub_s)  # 输出: World!sub_s = s[:5]  # 从开头到索引 5（不包括 5）
print(sub_s)  # 输出: Hellosub_s = s[::2]  # 每隔一个字符取一个
print(sub_s)  # 输出: Hlo ol!

str.find()与str.index()

使用 str.find() 方法查找子字符串时，如果子字符串不存在于原字符串中，find() 方法不会报错，而是返回 -1。 str.index()在找不到子字符串时会抛出 ValueError 异常。

str.find()

s = "Hello, World!"
index = s.find("World")
print(index)  # 输出: 7# 查找不存在的子字符串
index = s.find("Python")
print(index)  # 输出: -1

str.index()

s = "Hello, World!"
index = s.index("World")
print(index)  # 输出: 7# 查找不存在的子字符串，会抛出 ValueError
try:index = s.index("Python")
except ValueError:print("Substring not found")  # 输出: Substring not found

• str.find(substring)：返回子字符串在原字符串中的最低索引，如果找不到则返回 -1。
• str.index(substring)：返回子字符串在原字符串中的最低索引，如果找不到则抛出 ValueError。