前言

在Python中，字符串的格式化输出是一个常用的操作，可以通过多种方式实现。通过掌握这些字符串格式化方法，可以根据实际需求选择合适的方式来进行字符串输出，使代码更加清晰和易读。

主要的字符串格式化方法包括：

1. 百分号 % 操作符（老式格式化）
2. str.format() 方法（较为现代的格式化方式）
3. f-strings（格式化字符串字面值，Python 3.6及以上版本）

1. 百分号 % 操作符（老式格式化）

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

• %s：字符串
• %d：整数
• %f：浮点数
• %.2f：保留两位小数的浮点数

2. str.format() 方法（较为现代的格式化方式）

这是Python 3引入的一种更强大和灵活的字符串格式化方式。

name = "Alice"
age = 30

# 使用 str.format() 方法
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.

# 指定位置参数
formatted_string = "My name is {0} and I am {1} years old. {0} likes Python.".format(name, age)
print(formatted_string)  # 输出: My name is Alice and I am 30 years old. Alice likes Python.

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

# 格式化浮点数
pi = 3.141592653589793
formatted_string = "Pi is approximately {:.2f}.".format(pi)
print(formatted_string)  # 输出: Pi is approximately 3.14.

3. f-strings（格式化字符串字面值，Python 3.6及以上版本）

name = "Alice"
age = 30

# 使用 f-strings
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.

# 表达式支持
formatted_string = f"Next year, I will be {age + 1} years old."
print(formatted_string)  # 输出: Next year, I will be 31 years old.

# 格式化浮点数
pi = 3.141592653589793
formatted_string = f"Pi is approximately {pi:.2f}."
print(formatted_string)  # 输出: Pi is approximately 3.14.

4. 其他方法

• 模板字符串：使用 string.Template 类进行字符串替换，适合需要更多安全性和控制的场景。

from string import Template 
template = Template("My name is $name and I am $age years old.") 
formatted_string = template.substitute(name="Alice", age=30) 
print(formatted_string) # 输出: My name is Alice and I am 30 years old.

比较

• 百分号 % 操作符：简单直观，但不太灵活，适合简单的字符串格式化。
• str.format() 方法：功能强大，支持位置参数和关键字参数，适合复杂的格式化需求。
• f-strings：最简洁和高效，推荐在Python 3.6及以上版本中使用，支持内嵌表达式和高级格式化。

python文件示例

from string import Template

name = "Alice"
age = 30

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

name = "Alice"
age = 30

# 使用 str.format() 方法
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.

# 指定位置参数
formatted_string = "My name is {0} and I am {1} years old. {0} likes Python.".format(name, age)
print(formatted_string)  # 输出: My name is Alice and I am 30 years old. Alice likes Python.

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

# 格式化浮点数
pi = 3.141592653589793
formatted_string = "Pi is approximately {:.2f}.".format(pi)
print(formatted_string)  # 输出: Pi is approximately 3.14.

name = "Alice"
age = 30

# 使用 f-strings
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.

# 表达式支持
formatted_string = f"Next year, I will be {age + 1} years old."
print(formatted_string)  # 输出: Next year, I will be 31 years old.

# 格式化浮点数
pi = 3.141592653589793
formatted_string = f"Pi is approximately {pi:.2f}."
print(formatted_string)  # 输出: Pi is approximately 3.14.

template = Template("My name is $name and I am $age years old.")
formatted_string = template.substitute(name="Alice", age=30)
print(formatted_string)  # 输出: My name is Alice, and I am 30 years old.