Python中format的常见用法

一、填充

1、按默认顺序填充

python">name = "Alice"
age = 25
print("My name is {} and I am {} years old.".format(name, age))

输出：My name is Alice and I am 25 years old.

2、指定位置

python">name = "Bob"
age = 30
print("My name is {1} and I am {0} years old.".format(age, name))

输出：My name is Bob and I am 30 years old.

3、通过key来填充

python">name = "Charlie"
age = 35
print("My name is {name} and I am {age} years old.".format(name=name, age=age))

输出：My name is Charlie and I am 35 years old.

4、通过下标填充

python">names=['Alice', 9]
print("My name is {name[0]} and I am {name[1]} years old.".format(name=names))
print("My name is {0[0]} and I am {0[1]} years old.".format(names))

输出：
My name is Alice and I am 9 years old.
My name is Alice and I am 9 years old.

5、通过字典

python">table = {'Google': 1, 'Runoob': 2, 'Taobao': 3}
print('Runoob: {0[Runoob]:d}; Google: {0[Google]:d}; Taobao: {0[Taobao]:d}'.format(table))

输出：Runoob: 2; Google: 1; Taobao: 3

6、通过对象的属性

python">class
Names():name1='Kevin'name2='Tom'
print('hello {names.name1} i am {names.name2}'.format(names=Names))

输出结果为：hello Kevin i am Tom

二、格式化数字

b、d、o、x分别是二进制、十进制、八进制、十六进制。

数字格式输出描述
3.1415926 {:.2f} 3.14 保留小数点后两位
3.1415926 {:+.2f} 3.14 带符号保留小数点后两位
-1 {:+.2f} -1 带符号保留小数点后两位
2.71828 {:.0f} 3 不带小数
1000000 {:,} 1,000,000 以逗号分隔的数字格式
0.25 {:.2%} 25.00% 百分比格式
1000000000 {:.2e} 1.00E+09 指数记法
25 {0:b} 11001 转换成二进制
25 {0:d} 25 转换成十进制
25 {0:o} 31 转换成八进制
25 {0:x} 19 转换成十六进制

示例：

python">num = 3.14159
print("The value of pi is approximately {:.2f}.".format(num))

输出：The value of pi is approximately 3.14.

python">num = 3.14159
print("num1 {0:.2f}, num2 {1:.3f}.".format(num, num))

输出：num1 3.14, num2 3.142.

三、对齐与填充

数字格式输出描述
5 {:0>2} 05 数字补零 (填充左边, 宽度为2)
5 {:x<4} 5xxx 数字补x (填充右边, 宽度为4)
10 {:x^4} x10x 数字补x (填充两边, 宽度为4)
13 {:10} 13 右对齐 (默认, 宽度为10)
13 {:<10} 13 左对齐 (宽度为10)
13 {:^10} 13 中间对齐 (宽度为10)

示例：{:<10} 表示左对齐，占用10个字符的宽度

python">name = "Alice"
print("Name: {} Age: {}".format(name, 25))
print("Name: {:<6} Age: {}".format(name, 25))
print("Name: {:10} Age: {}".format(name, 25))
print("Name: {:<10} Age: {}".format(name, 25))
输出结果为：
Name: Alice Age: 25
Name: Alice  Age: 25
Name: Alice      Age: 25
Name: Alice      Age: 25

python">num1 = 1
print('{0:2d}'.format(num1))
print('{0:3d}'.format(num1))
print('{0:4d}'.format(num1))

输出：

python">num1 = 1
print('{0:2f}'.format(num1))
print('{0:3.2f}'.format(num1))
print('{0:5.2f}'.format(num1))

输出结果为：

1.000000
1.001.00

python">str1 = 'hello'
num1 = 1
print('{0}==>{1}'.format(str1, num1))
print('{0} ==> {1}'.format(str1, num1))
print('{0:5} ==> {1:1d}'.format(str1, num1))
print('{0:6} ==> {1:2d}'.format(str1, num1))
print('{0:7} ==> {1:3d}'.format(str1, num1))
print('{0:8} ==> {1:4d}'.format(str1, num1))
print('{0:9} ==> {1:5d}'.format(str1, num1))

输出：

hello==>1
hello ==> 1
hello ==> 1
hello  ==>  1
hello   ==>   1
hello    ==>    1
hello     ==>     1

四、格式化日期和时间

python">from datetime import datetime
now = datetime.now()
print("Current date and time: {:%Y-%m-%d %H:%M:%S}".format(now))

输出：Current date and time: 2022-01-01 12:00:00

五、使用 f-string

Python 3.6及以上版本支持使用 f-string 来格式化字符串

python">name = "Alice"
age = 25
print(f"My name is {name} and I'm {age} years old.")

输出：My name is Alice and I’m 25 years old.

六、旧式字符串格式化

python">import math
print('常量 PI 的值近似为：%5.3f。' % math.pi)

输出：常量 PI 的值近似为：3.142。