【Python】 str.format()字符串格式化

str.format()是在python3中引入的字符串格式化方法，可以用来对字符串输出进行替换。其语法格式为:

{}.format(value)

例如单个字符串替换:

In [1]: print("{}, Is anybody in there?".format("hello"))
hello, Is anybody in there?

多个字符串替换，为顺序替换:

In [3]: print("{}, is anybody in {}".format("hello", "there"))
hello, is anybody in there

在{}里面定义使用format中值的顺序:

In [2]: print("{1} is an, {0}".format("ItchyHacker", "AI"))
AI is an, ItchyHacker

str中第一个{}为1, 第二个为0, 因此分别对应为"AI"和”ItchyHacker"
在{}中第一个替换值的key，并且在format中通过key指定值。

In [5]: print("{name} is an, {obj}".format(name="ItchyHacker", obj="AI"))
ItchyHacker is an, AI

通过在{}中使用占位符对输出进行定制:
输出数据类型的指定:

s – strings
d – decimal integers (base-10)
f – floating point display
c – character
b – binary
o – octal
x – hexadecimal with lowercase letters after 9
X – hexadecimal with uppercase letters after 9
e – exponent notation

例如:

In [7]: print("{name:s} is {height:f}m high, and weights {weight:d}kg".format(name="
   ...: ItchyHacker", height=1.75, weight=70))
ItchyHacker is 1.750000m high, and weights 70kg

指定输出的长度和使用占位符号:

数字:  输出占多少位
.数字: 保留小数点多少位
0数字: 以0为占位符号

身高用.2f限制输出小数点后两位，体重使用04d限制输出4位，同时使用0为占位符号。没有0的话就是空格作为占位符号。

In [8]: print("{name:s} is {height:.2f}m high, and weights {weight:04d}kg".format(na
   ...: me="ItchyHacker", height=1.75, weight=70))
ItchyHacker is 1.75m high, and weights 0070kg

指定对齐方式:

<   :  left-align text in the field
^   :  center text in the field
>   :  right-align text in the field

体重右边对齐:

In [9]: print("{name:s} is {height:.2f}m high, and weights {weight:>6d}kg".format(na
   ...: me="ItchyHacker", height=1.75, weight=70))
ItchyHacker is 1.75m high, and weights     70kg