一、字符串的基本操作
1.1 创建字符串
# 三种创建方式
str1 = '单引号字符串'
str2 = "双引号字符串"
str3 = '''三引号字符串，
可以跨多行'''1.2 字符串索引和切片
s = "Hello, Python!"
# 索引
print(s[0]) # H (第一个字符)
print(s[-1]) # ! (最后一个字符)
print(s[7]) # P
# 切片
print(s[0:5]) # Hello (包含起点，不包含终点)
print(s[7:]) # Python! (从索引7到末尾)
print(s[:5]) # Hello (从头到索引4)
print(s[-7:-1]) # Python (负索引切片)
print(s[::2]) # HloPto! (步长为2)二、常用的字符串方法
2.1 大小写转换
s = "hello World"
print(s.upper()) # HELLO WORLD
print(s.lower()) # hello world
print(s.capitalize()) # Hello world
print(s.title()) # Hello World
print(s.swapcase()) # HELLO wORLD2.2 查找和替换
s = "Hello, Python! Python is great."
# 查找
print(s.find("Python")) # 7 (返回第一次出现的索引)
print(s.rfind("Python")) # 15 (从右边开始查找)
print(s.index("Python")) # 7 (类似find，但找不到会报错)
print(s.rindex("Python")) # 15
# 替换
print(s.replace("Python", "Java")) # Hello, Java! Java is great.
print(s.replace("Python", "Java", 1)) # 只替换一次
# 检查开头和结尾
print(s.startswith("Hello")) # True
print(s.endswith("great.")) # True2.3 分割和连接
s = "apple,banana,orange"
# 分割
print(s.split(",")) # ['apple', 'banana', 'orange']
print(s.split(",", 1)) # ['apple', 'banana,orange'] (最多分割1次)
s2 = "line1\nline2\nline3"
print(s2.splitlines()) # ['line1', 'line2', 'line3']
# 分区
print(s.partition(",")) # ('apple', ',', 'banana,orange')
print(s.rpartition(",")) # ('apple,banana', ',', 'orange')
# 连接
list_fruits = ['apple', 'banana', 'orange']
print(",".join(list_fruits)) # apple,banana,orange2.4 去除空白字符
s = " hello world \t\n"
print(s.strip()) # "hello world" (去除两边空白)
print(s.lstrip()) # "hello world \t\n" (去除左边空白)
print(s.rstrip()) # " hello world" (去除右边空白)
# 去除指定字符
s2 = "***hello***"
print(s2.strip("*")) # "hello"2.5 判断方法
s1 = "Hello123"
s2 = "12345"
s3 = "HELLO"
s4 = "hello"
s5 = "Hello World"
s6 = " "
print(s1.isalnum()) # True (字母或数字)
print(s1.isalpha()) # False (纯字母)
print(s2.isdigit()) # True (纯数字)
print(s3.isupper()) # True (全大写)
print(s4.islower()) # True (全小写)
print(s5.istitle()) # True (每个单词首字母大写)
print(s6.isspace()) # True (全是空白字符)
print(s1.isascii()) # True (ASCII字符)2.6 对齐和填充
s = "hello"
print(s.center(11, "*")) # ***hello***
print(s.ljust(10, "-")) # hello-----
print(s.rjust(10, "-")) # -----hello
print(s.zfill(10)) # 00000hello2.7 计数和长度
s = "hello world, hello python"
print(len(s)) # 25 (字符串长度)
print(s.count("hello")) # 2 (子字符串出现次数)
print(s.count("l")) # 4 (字符出现次数)
print(s.count("o", 0, 10)) # 1 (在指定范围内计数)三、字符串格式化
3.1 传统格式化（%）
name = "Alice"
age = 25
print("Name: %s, Age: %d" % (name, age))
print("Price: %.2f" % 99.987) # 99.99
print("Percent: %d%%" % 80) # 80%3.2 format()方法
# 位置参数
print("{} is {} years old".format("Alice", 25))
# 关键字参数
print("{name} is {age} years old".format(name="Bob", age=30))
# 索引
print("{1} comes before {0}".format("B", "A"))
# 格式化数字
print("Price: {:.2f}".format(99.987)) # 99.99
print("Hex: {:x}".format(255)) # ff
print("Percent: {:.1%}".format(0.8)) # 80.0%3.3 f-string（Python 3.6+）
name = "Alice"
age = 25
height = 1.65
print(f"{name} is {age} years old")
print(f"Price: {99.987:.2f}") # 99.99
print(f"Hex: {255:x}") # ff
print(f"Expression: {age * 2}") # 50
print(f"Height: {height:.2f}m") # 1.65m四、字符串编码和转换
4.1 编码转换
s = "你好，世界"
# 编码为字节
b = s.encode("utf-8") # b'\xe4\xbd\xa0\xe5\xa5\xbd\xef\xbc\x8c\xe4\xb8\x96\xe7\x95\x8c'
b2 = s.encode("gbk")
# 解码为字符串
s2 = b.decode("utf-8")
print(s2) # 你好，世界4.2 maketrans和translate
# 创建转换表
trans_table = str.maketrans("aeiou", "12345")
s = "hello world"
print(s.translate(trans_table)) # h2ll4 w4rld
# 删除指定字符
trans_table2 = str.maketrans("", "", "aeiou")
print(s.translate(trans_table2)) # hll wrld五、其他有用的方法
5.1 expandtabs()
s = "Name\tAge\tCity"
print(s.expandtabs(20))
# Name Age City5.2 partition() 和 rpartition()
url = "www.example.com/page"
print(url.partition(".")) # ('www', '.', 'example.com/page')
print(url.rpartition(".")) # ('www.example', '.', 'com/page')5.3 检查内容
s1 = "Hello123"
s2 = "123"
s3 = "Hello"
print(s1.isalnum()) # True (字母或数字)
print(s2.isdecimal()) # True (十进制数字)
print(s3.isalpha()) # True (纯字母)
print(s2.isnumeric()) # True (数值字符)六、字符串性能优化技巧
6.1 使用join代替+
# 不推荐 - 创建多个临时字符串
result = ""
for i in range(10000):
result += str(i)
# 推荐 - 更高效
parts = []
for i in range(10000):
parts.append(str(i))
result = "".join(parts)6.2 使用in进行成员检查
s = "hello world"
# 检查子字符串
if "world" in s:
print("Found!")
# 检查字符
if "h" in s:
print("Contains 'h'")七、实用示例
7.1 数据清洗
def clean_string(text):
"""清洗字符串"""
# 去除空白字符
text = text.strip()
# 转换为小写
text = text.lower()
# 替换多个空格为单个空格
import re
text = re.sub(r'\s+', ' ', text)
return text
sample = " Hello World \n"
print(clean_string(sample)) # "hello world"7.2 字符串验证
def validate_input(input_str):
"""验证用户输入"""
if not input_str:
return "输入不能为空"
if len(input_str) < 3:
return "输入太短"
if not input_str.isalnum():
return "只能包含字母和数字"
return "输入有效"
print(validate_input("abc123")) # 输入有效
print(validate_input("ab")) # 输入太短7.3 模板生成
def generate_email_template(name, product):
"""生成邮件模板"""
template = """
尊敬的{name}：
感谢您购买{product}！
如有任何问题，请随时联系我们。
祝好！
客服团队
"""
return template.format(name=name, product=product)
print(generate_email_template("张三", "Python编程书籍"))总结
记住：字符串是不可变对象，所有字符串方法都不会修改原字符串，而是返回一个新的字符串。
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