Python更改REPR浮动数字

问题描述

好的，我想使用repr()打印出一堆列表和嵌套数组的文本版本.

Okay, I want to use repr() to print out a text version of a bunch of lists and nested arrays.

但是我希望数字只保留小数点后4位，而不是:42.7635745114，而是32.7635.

But I want the numbers to have only 4 decimal places not: 42.7635745114 but 32.7635.

我想使用repr()，因为它具有很好的处理嵌套数组的能力.编写自己的打印循环是一种没有吸引力的选择.

I'd like to use repr() because of its nice ability to handle nested arrays. Writing my own print loop is an unattractive option.

当然有某种方法可以使repr重载吗?我看到有一个repr和reprlib模块，但是示例确实很少，就像不存在一样.

Surely there is some way to overload repr to do this? I see there is a repr and reprlib modules but examples are really scarce, like nonexistent.

推荐答案

不，没有办法使repr()重载.浮点数的格式在C源代码中进行了硬编码.

No, there is no way to overload repr(). The format for floats is hardcoded in the C source code.

float_repr()函数调用一个'r'格式化程序的辅助函数，最终会调用实用程序将格式硬编码为的功能，最终归结为format(float, '.16g').

The float_repr() function calls a helper function with the 'r' formatter, which eventually calls a utility function that hardcodes the format to what comes down to format(float, '.16g').

您可以继承float的子类，但仅这样做来表示值(尤其是在较大的结构中)就太过分了.这是repr(Python 3中的reprlib)出现的地方；该库旨在打印任意数据结构的有用表示形式，并让您着迷于在该结构中打印特定类型.

You could subclass float, but to only do that for representing values (especially in a larger structure) is overkill. This is where repr (reprlib in Python 3) comes in; that library is designed to print useful representations of arbitrary data structures, and letting you hook into printing specific types in that structure.

您可以通过子类化 repr.Repr()来使用repr模块. ，提供用于处理浮点的repr_float()方法:

You could use the repr module by subclassing repr.Repr(), providing a repr_float() method to handle floats:

try:  # Python 3
    import reprlib
except ImportError:  # Python 2
    import repr as reprlib

class FloatRepr(reprlib.Repr):
    def repr_float(self, value, level):
        return format(value, '.4f')

print(FloatRepr().repr(object_to_represent))

演示:

>>> import random
>>> import reprlib
>>> class FloatRepr(reprlib.Repr):
...     def repr_float(self, value, level):
...         return format(value, '.4f')
...
>>> print(FloatRepr().repr([random.random() for _ in range(5)]))
[0.5613, 0.9042, 0.3891, 0.7396, 0.0140]

您可能想在子类上设置max*属性，以影响每种容器类型打印多少个值.

You may want to set the max* attributes on your subclass to influence how many values are printed per container type.

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