格式化字符串

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实例的字符串显示

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class Pair:
    def __init__(self, x, y):
        self.x = x
        self.y = y

    def __repr__(self):
        return f'({self.x}, {self.y})'


    def __str__(self):
        return f'Pair({self.x=}, {self.y=})'

p = Pair(3, 4)
print(p)

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from dataclasses import dataclass

@dataclass
class Pair:
    x:int
    y:int = 0  # y 默认值为0
p = Pair(3, 4)
print(p)

对象自定义格式化

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_formats = {
    'ymd': '{d.year}-{d.month}-{d.day}',
    'mdy': '{d.month}/{d.day}/{d.year}',
    'dmy': '{d.day}/{d.month}/{d.year}'
}


class Date:
    def __init__(self, year, month, day):
        self.year = year
        self.month = month
        self.day = day

    def __format__(self, code):
        if code == '':
            code = 'ymd'
        fmt = _formats[code]
        return fmt.format(d=self)


d = Date(2012, 12, 21)
print(d)
print(format(d, 'mdy'))
print('The date is {:ymd}'.format(d))
print('The date is {:mdy}'.format(d))

修改后

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from dataclasses import dataclass
_formats = {
    'ymd': '{d.year}-{d.month}-{d.day}',
    'mdy': '{d.month}/{d.day}/{d.year}',
    'dmy': '{d.day}/{d.month}/{d.year}'
}

@dataclass
class Date:
    year:int 
    month:int
    day:int

    def __format__(self, code):
        if code == '':
            code = 'ymd'
        fmt = _formats[code]
        return fmt.format(d=self)


a = Date(2012, 12, 21)
print(a)
print(format(a, 'mdy'))
print('The date is {:ymd}'.format(a))
print('The date is {:mdy}'.format(a))