python中str的用法 python字符串str类型的转换方法

my_string = 'Hello, World!'
another_string = "Python is awesome"

# 连接字符串
greeting = my_string + " " + another_string
print(greeting)  # 输出: Hello, World! Python is awesome

# 切片
print(my_string[0:5])  # 输出: Hello

# 查找子串
print(my_string.find('World'))  # 输出: 7

# 字符串到整数
num_str = "123"
num_int = int(num_str)
print(num_int)  # 输出: 123

# 字符串到浮点数
float_str = "3.14"
float_num = float(float_str)
print(float_num)  # 输出: 3.14

try:
    num = int("abc")
except ValueError:
    print("转换失败，字符串不是有效的整数")

# 整数到字符串
num = 42
str_num = str(num)
print(str_num)  # 输出: 42

# 浮点数到字符串
pi = 3.14159
str_pi = str(pi)
print(str_pi)  # 输出: 3.14159

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

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

# 使用格式说明符
pi = 3.14159
formatted_pi = "Pi is approximately {:.2f}".format(pi)
print(formatted_pi)  # 输出: Pi is approximately 3.14

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

# 使用表达式
x = 10
y = 20
result = f"The sum of {x} and {y} is {x + y}"
print(result)  # 输出: The sum of 10 and 20 is 30

text = "Hello, 世界"
encoded_text = text.encode('utf-8')
print(encoded_text)  # 输出: b'Hello, \xe4\xb8\x96\xe7\x95\x8c'

encoded_text = b'Hello, \xe4\xb8\x96\xe7\x95\x8c'
decoded_text = encoded_text.decode('utf-8')
print(decoded_text)  # 输出: Hello, 世界

encoded_text = b'Hello, \xe4\xb8\x96\xe7\x95\x8c'
try:
    decoded_text = encoded_text.decode('ascii')
except UnicodeDecodeError:
    print("解码失败，尝试使用UTF-8编码")
    decoded_text = encoded_text.decode('utf-8', errors='ignore')
print(decoded_text)  # 输出: Hello, 世界

# 低效的字符串连接
result = ""
for i in range(1000):
    result += str(i)

# 使用join()方法优化
result = ''.join(str(i) for i in range(1000))

# 使用strip()方法去除首尾空白
text = "   Hello, World!   "
cleaned_text = text.strip()
print(cleaned_text)  # 输出: Hello, World!

# 使用列表来构建字符串
chars = list("Hello")
chars[0] = 'J'
result = ''.join(chars)
print(result)  # 输出: Jello

name = "David"
age = 40
formatted_string = f"My name is {name} and I am {age} years old."
print(formatted_string)  # 输出: My name is David and I am 40 years old.