Python学习笔记：格式化输出之f-string、format、%
一、%占位符
1.说明
# 符号代表意义
%s -- 字符串
%10s -- 指定长度 左填充
%-10s -- 指定长度 右填充
%f -- 浮点数
%.2f -- 保留2位小数点
%d -- 整数
2.实操
a = 'Name'
b = 'Hider'
c = 100
d = 1.80
print("My %s is %s." % (a, b))
# My Name is Hider.
print("My %s is %s. And my age is %d. My height is %f." % (a, b, c, d))
# My Name is Hider. And my age is 100. My height is 1.800000.
%f 默认精度是保留后6位，可通过 %.2f 设置。
print("My %s is %s. And my age is %d. My height is %.2f." % (a, b, c, d))
# My Name is Hider. And my age is 100. My height is 1.80.
字符串长度填充。
# 左填充
print('%10s' % ('Hider')) # Hider
# 右填充
print('%-10s' % ('Hider')) # Hider
二、f-string格式化
f-string 直接使用变量名填充句子当中的内容。
Python 3.6 及以后版本支持 f-string 格式化输出字符串。优先推荐！！！
a = 'Name'
b = 'Hider'
print(f'My {a} is {b}.')
# My Name is Hider.
print(f'计算结果为：{2*5 + 3*10}')
# 计算结果为：40
string_test = 'ABC'
print(f'It\'s {string_test.lower()}')
# It's abc
三、format关键字
1.格式化输出
format 关键字用来格式化输出字符串。不同入参情况：
- 不指定位置
a = 'Name'
b = 'Hider'
c = 100
d = 1.80
print('My {} is {}.'.format(a,b))
# My Name is Hider.
位置默认开始从 0 计算，然后对应位置填入数据。
- 指定位置
a = 'Name'
b = 'Hider'
c = 100
d = 1.80
print('My {0} is {1}. And my age is {2}.'.format(a,b,c))
# My Name is Hider. And my age is 100.
print('My {1} is {2}. And my age is {0}.'.format(a,b,c))
# My Hider is 100. And my age is Name.
- 关键字配对
print('My {a} is {b}. And my age is {c}.'.format(a=10,b=20,c=30))
# My 10 is 20. And my age is 30.
- 字典参数
dic = {'a':10, 'b':20, 'c':30}
print('My {a} is {b}. And my age is {c}.'.format(**dic))
# My 10 is 20. And my age is 30.
- 列表参数
lis = ['a','b','c']
s = 'i like {} and {} and {}.'.format(*lis)
print(s)
# i like a and b and c.
2.精度
pi = 3.1415926535
print('{:.2f}'.format(pi)) # 3.14
print('{:+.3f}'.format(pi)) # +3.142
print('{:.2%}'.format(pi)) # 314.16%
3.千分位分隔符
主要用于货币数据的格式化输出。
a = 1000000000
print('{:,}'.format(a)) # 1,000,000,000
# 添加货币符号
print('${:,}'.format(a)) # $1,000,000,000
