python中format的使用

在Python中，format是一个字符串方法，用于将值插入到字符串中。它是一种更方便和灵活的替代方法，用于将变量插入到字符串中。

使用示例：

1. 基本用法

name = 'Tom'
age = 25
print('My name is {} and I am {} years old.'.format(name, age))
# Output: My name is Tom and I am 25 years old.

2. 指定参数位置

name = 'Tom'
age = 25
print('My name is {0} and I am {1} years old. {0} is my name.'.format(name, age))
# Output: My name is Tom and I am 25 years old. Tom is my name.

3. 指定参数名称

person = {'name': 'Tom', 'age': 25}
print('My name is {name} and I am {age} years old.'.format(**person))
# Output: My name is Tom and I am 25 years old.

4. 格式化数字

num = 1234.5678
print('The number is {:.2f}'.format(num))
# Output: The number is 1234.57

5. 格式化日期和时间

from datetime import datetime
now = datetime.now()
print('Today is {:%Y-%m-%d %H:%M:%S}'.format(now))
# Output: Today is 2021-05-20 09:30:00

6. 使用占位符

name = 'Tom'
age = 25
print('My name is %s and I am %d years old.' % (name, age))
# Output: My name is Tom and I am 25 years old.

注意：占位符方式已经过时，推荐使用format方法。