python中字符串常见操作全解析

# 单行字符串
name = 'Python'
slogan = "Life is short, use Python"

# 多行字符串（常用于文档字符串或长文本）
multiline = """这是一个
多行字符串的
示例"""

s = "HelloPython"

print(s[0])       # 'H'
print(s[-1])      # 'n'
print(s[0:5])     # 'Hello' (提取索引 0 到 4)
print(s[5:])      # 'Python' (从索引 5 到结束)
print(s[::-1])    # 'nohtyPolleH' (字符串反转)

a = "Hello"
b = "World"
print(a + " " + b)  # "Hello World"
print(a * 3)        # "HelloHelloHello"

text = "python programming"
print(text.upper())      # "PYTHON PROGRAMMING"
print(text.capitalize()) # "Python programming"
print(text.title())      # "Python Programming"

user_input = "  admin  "
print(user_input.strip())  # "admin" (去除两端空格)

sentence = "I like Java"
new_sentence = sentence.replace("Java", "Python")
print(new_sentence)  # "I like Python"

print(sentence.find("like")) # 返回索引 2，若不存在返回 -1

# 分割：字符串 -> 列表
csv_data = "apple,banana,orange"
fruits = csv_data.split(",") # ['apple', 'banana', 'orange']

# 合并：列表 -> 字符串
new_data = "-".join(fruits)  # "apple-banana-orange"

name = "Alice"
age = 25
# 使用 f-string
message = f"Hello, my name is {name} and I am {age} years old."
print(message)

# 支持表达式运算
print(f"Next year, I will be {age + 1}.")

s = "Python"
# s[0] = "J"  # ❌ 报错：TypeError: 'str' object does not support item assignment
s = "J" + s[1:] # ✅ 正确做法：创建一个新字符串