Python新手入门必备之字符串操作全攻略指南

# 使用单引号
str1 = 'Hello, Python!'
print(str1)

# 使用双引号
str2 = "你好，世界！"
print(str2)

# 如果字符串中包含单引号，可以使用双引号包裹
str3 = "I'm a Python beginner."
print(str3)

# 如果字符串中包含双引号，可以使用单引号包裹
str4 = 'He said, "Python is great!"'
print(str4)

# 使用三引号创建多行字符串
multiline_str = """
这是一个
多行字符串的例子。
它保留了原始的格式。
"""
print(multiline_str)

# 三引号也可以用于单行字符串，但通常不推荐
single_line_triple = '''Hello'''
print(single_line_triple)

my_string = "Python"

# 访问第一个字符 (索引0)
print(f"第一个字符: {my_string[0]}") # 输出: P

# 访问第三个字符 (索引2)
print(f"第三个字符: {my_string[2]}") # 输出: t

# 访问最后一个字符 (索引-1)
print(f"最后一个字符: {my_string[-1]}") # 输出: n

# 访问倒数第三个字符 (索引-3)
print(f"倒数第三个字符: {my_string[-3]}") # 输出: h

my_string = "Hello Python"

# 从索引0到索引5 (不包含5)
print(f"切片 [0:5]: {my_string[0:5]}") # 输出: Hello

# 从索引6到末尾
print(f"切片 [6:]: {my_string[6:]}") # 输出: Python

# 从开头到索引5 (不包含5)
print(f"切片 [:5]: {my_string[:5]}") # 输出: Hello

# 复制整个字符串
print(f"切片 [:]: {my_string[:]}") # 输出: Hello Python

# 使用负数索引进行切片
print(f"切片 [-6:]: {my_string[-6:]}") # 输出: Python

# 使用步长：每隔一个字符取一个
print(f"切片 [::2]: {my_string[::2]}") # 输出: HloPto

# 翻转字符串 (步长为-1)
print(f"翻转字符串: {my_string[::-1]}") # 输出: nohtyP olleH

my_string = "Python"
# my_string[0] = 'J' # 这会引发 TypeError: 'str' object does not support item assignment

original_string = "Python"
new_string = 'J' + original_string[1:]
print(f"原字符串: {original_string}") # 输出: Python
print(f"新字符串: {new_string}")     # 输出: Jython

text = "Hello World"
length = len(text)
print(f"字符串 '{text}' 的长度是: {length}") # 输出: 11

str1 = "Hello"
str2 = "Python"
combined_str = str1 + ", " + str2 + "!"
print(f"连接后的字符串: {combined_str}") # 输出: Hello, Python!

word = "Ha"
repeated_word = word * 3
print(f"重复后的字符串: {repeated_word}") # 输出: HaHaHa

sentence = "Python is fun!"
print(f"'Python' 在 sentence 中吗? {'Python' in sentence}") # 输出: True
print(f"'java' 在 sentence 中吗? {'java' in sentence}")   # 输出: False

text = "hello world hello python"
print(f"'world' 的位置: {text.find('world')}") # 输出: 6
print(f"'python' 的位置: {text.find('python')}") # 输出: 18
print(f"'java' 的位置: {text.find('java')}")   # 输出: -1

# 可以指定搜索的起始位置
print(f"从索引7开始查找 'hello' 的位置: {text.find('hello', 7)}") # 输出: 12

text = "hello world"
print(f"'world' 的位置: {text.index('world')}") # 输出: 6

try:
    text.index('java')
except ValueError as e:
    print(f"查找 'java' 失败: {e}") # 输出: 查找 'java' 失败: substring not found

original_text = "I like apples, apples are healthy."
new_text = original_text.replace("apples", "bananas")
print(f"替换后的字符串: {new_text}") # 输出: I like bananas, bananas are healthy.

# 替换指定数量
limited_replace = original_text.replace("apples", "oranges", 1)
print(f"限制替换一次: {limited_replace}") # 输出: I like oranges, apples are healthy.

data = "apple,banana,cherry"
fruits = data.split(',')
print(f"按逗号分割: {fruits}") # 输出: ['apple', 'banana', 'cherry']

sentence = "This is a sample sentence."
words = sentence.split() # 默认按空白字符分割
print(f"按空白分割: {words}") # 输出: ['This', 'is', 'a', 'sample', 'sentence.']

path = "/usr/local/bin"
parts = path.split('/', 2) # 最大分割2次
print(f"限制分割次数: {parts}") # 输出: ['', 'usr', 'local/bin']

my_list = ['Python', 'is', 'awesome']
joined_string = " ".join(my_list)
print(f"用空格连接列表: {joined_string}") # 输出: Python is awesome

fruits_list = ['apple', 'banana', 'cherry']
comma_separated = ", ".join(fruits_list)
print(f"用逗号和空格连接列表: {comma_separated}") # 输出: apple, banana, cherry

text = "Hello Python World"
print(f"大写: {text.upper()}")      # 输出: HELLO PYTHON WORLD
print(f"小写: {text.lower()}")      # 输出: hello python world
print(f"首字母大写: {text.capitalize()}") # 输出: Hello python world
print(f"标题格式: {text.title()}")     # 输出: Hello Python World
print(f"大小写互换: {text.swapcase()}") # 输出: hELLO pYTHON wORLD

padded_text = "   Hello World   \n"
print(f"原始字符串: '{padded_text}'")
print(f"去除两端空白: '{padded_text.strip()}'") # 输出: 'Hello World'

email = "user@example.com   "
print(f"去除右侧空白: '{email.rstrip()}'") # 输出: 'user@example.com'

filename = "###data.txt###"
print(f"去除指定字符: '{filename.strip('#')}'") # 输出: 'data.txt'

print(f"'123'.isdigit(): {'123'.isdigit()}")       # 输出: True
print(f"'abc'.isalpha(): {'abc'.isalpha()}")       # 输出: True
print(f"'abc123'.isalnum(): {'abc123'.isalnum()}")   # 输出: True
print(f"' '.isspace(): {' '.isspace()}")         # 输出: True
print(f"'HELLO'.isupper(): {'HELLO'.isupper()}")   # 输出: True
print(f"'hello'.islower(): {'hello'.islower()}")   # 输出: True

print(f"'Hello'.isalpha(): {'Hello'.isalpha()}")     # 输出: True (混合大小写仍是字母)
print(f"'Hello World'.isalpha(): {'Hello World'.isalpha()}") # 输出: False (包含空格)

name = "Alice"
age = 30
print("My name is %s and I am %d years old." % (name, age))
# 输出: My name is Alice and I am 30 years old.

name = "Bob"
age = 25
print("My name is {} and I am {} years old.".format(name, age))
# 输出: My name is Bob and I am 25 years old.

# 可以通过索引或关键字参数指定顺序
print("My name is {0} and I am {1} years old. {0} likes Python.".format(name, age))
print("My name is {n} and I am {a} years old.".format(n=name, a=age))

name = "Charlie"
age = 35
print(f"My name is {name} and I am {age} years old.")
# 输出: My name is Charlie and I am 35 years old.

# 可以在花括号内直接进行表达式计算
price = 19.99
quantity = 3
print(f"Total: ${price * quantity:.2f}") # .2f 表示保留两位小数
# 输出: Total: $59.97

my_str = "abc"
# my_str[0] = 'd' # 错误！
my_str = 'd' + my_str[1:] # 正确，创建新字符串
print(my_str) # 输出: dbc

s = "Python"
# print(s[10]) # 错误！IndexError: string index out of range

# 示例：文件读取时的编码
# with open('my_file.txt', 'r', encoding='utf-8') as f:
#     content = f.read()