chapter3 使用字符串

concepts and notations

concepts

1. 字符串不可变；

notations

%s	转换说明符，将指定值转换为字符串类型
%.3f	带有3位小数的浮点数

设置字符串格式

method1：格式设置运算符%

• 针对单个值（string or number）
• 针对多个值（tuple）

>>> format = "Hello, %s. %s enought for ya?"
>>> values = ('world', 'Hot')
>>> format % values

method2：字符串方法format

# 待替换字段-无名称
>>> "{}, {} and {}".format("first", "second", "third")
'first, second, third'

# 待替换字段-以索引为名称
>>> "{0}, {1} and {2}".format("first", "second", "third")
'first, second and third'
>>> "{3}, {0}, {2}, {1}, {3}, {0}".format("be", "not", "or", "to")
'to be or not to be'

# 替换多个字段，参数顺序无关紧要
# 指定格式说明符.2f（带有2位小数的浮点数），用冒号将格式说明符与字段名隔开
>>> from math import pi
>>> "{name} is approximately {value: .2f}.".format(value = pi, name = "pi")

# 变量与待替换字段同名，可使用f字符串（f""）
>>> from math import e
>>> f"Eluer's constant is roughly {e}"
>>> "Eluer's constant is rougtly 2.718281828459045"