相关疑难解决方法(0)

根据Python 2.7.12文档:

!s(apply str())和!r(apply repr())可用于在格式化之前转换值.

>>> import math
>>> print 'The value of PI is approximately {}.'.format(math.pi)
The value of PI is approximately 3.14159265359.
>>> print 'The value of PI is approximately {!r}.'.format(math.pi)
The value of PI is approximately 3.141592653589793.

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有趣的是,转换后的值是输出repr(),而不是str().

>>> str(math.pi)
'3.14159265359'
>>> repr(math.pi)
'3.141592653589793'

那么"转换价值"在这里意味着什么呢？使它不那么人性化？

实现__repr__了一类Foo有成员变量x和y,是有办法来自动填充字符串？不起作用的示例:

class Foo(object):
    def __init__(self, x, y):
        self.x = x
        self.y = y
    def __repr__(self):
        return "Foo({})".format(**self.__dict__)

>>> foo = Foo(42, 66)
>>> print(foo)
IndexError: tuple index out of range

而另一个:

from pprint import pprint
class Foo(object):
    def __init__(self, x, y):
        self.x = x
        self.y = y
    def __repr__(self):
        return "Foo({})".format(pprint(self.__dict__))

>>> foo = Foo(42, 66)
>>> print(foo)
{'x': 42, 'y': 66}
Foo(None)

是的我可以将方法定义为

    def __repr__(self):
        return "Foo({x={}, y={}})".format(self.x, self.x)

但是当有许多成员变量时,这会变得乏味.