使用 vars 或 __dict__ 的 Python 固定宽度字符串格式

Question

我正在处理一个 Python 项目，我希望使用一些快捷方式来帮助格式化字符串中的类数据。更具体地说，我希望能够使用类似于 '{a}{b}{c}'.format(**vars(self), [strlen, strlen, strlen]) 的东西并指定显示的每个属性的字符串长度。例如:

class Dummy(object):
    def __init__(self):
        self.value1 = 'A VALUE'
        self.value2 = 'ANOTHER VALUE'
        self.value3 = 'THIRD VALUE'

    def to_s(self):
        # want value1 to be 20 chars
        # value2 to be 8 chars
        # value3 to be 10 chars
        # is something similar to this possible
        return '{value1},{value2},{value3}'.format(**vars(self), [20, 8, 10])


    def to_s2(self):
        # or will I have to reference each explicitly and specify the either padding or slicing?
        return '{},{},{}'.format(self.value1.ljust(20), self.value2[:8], self.value3[:10])

我知道这是不可能的，但是其中有几个类有 30 或 40 个属性，如果可行的话，这会让生活变得容易得多。

谢谢。

Answer 1

您可以在 {} 字段中嵌套 {} 字段，但只允许嵌套一层。幸运的是，实际上只需要一层嵌套。 :)

来自 Format String Syntax :

A format_spec field can also include nested replacement fields within it. These nested replacement fields may contain a field name, conversion flag and format specification, but deeper nesting is not allowed. The replacement fields within the format_spec are substituted before the format_spec string is interpreted. This allows the formatting of a value to be dynamically specified.

class Dummy(object):
    def __init__(self):
        self.value1 = 'A VALUE'
        self.value2 = 'ANOTHER VALUE'
        self.value3 = 'THIRD VALUE'

    def __str__(self):
        # want value1 to be 20 chars
        # value2 to be 8 chars
        # value3 to be 10 chars
        return '{value1:{0}},{value2:{1}},{value3:{2}}'.format(*[20, 8, 10], **vars(self))

print(Dummy())

输出

A VALUE             ,ANOTHER VALUE,THIRD VALUE