Question

从开始，@ AshwiniChaudhary给出了一个很好的答案来创建一个具有不同set（）函数的新(X,Y) = (164,92)对象：

A = fft2(double(Im)/255.0);
>> Ashifted = fftshift(A);
>> Ashifted(97,158)
ans =   7.4484 - 10.4582i
>> Ashifted(93,165)
ans =  12.1928 -  4.9850i

为了允许用户定义的char / str附加到密钥，我尝试过：

Counter

但它正在返回一个空柜台：

from collections import Counter

class CustomCounter(Counter):
    def __setitem__(self, key, value):
        if len(key) > 1 and not key.endswith(u"\uE000"):
            key += u"\uE000"
        super(CustomCounter, self).__setitem__(key, value)

那是因为我错过了from collections import Counter, defaultdict class AppendedStrCounter(Counter): def __init__(self, str_to_append): self._appended_str = str_to_append super(AppendedStrCounter, self).__init__() def __setitem__(self, key, value): if len(key) > 1 and not key.endswith(self._appended_str): key += self._appended_str super(AppendedStrCounter, self).__setitem__(tuple(key), value)中的iter：

>>> class AppendedStrCounter(Counter):
...     def __init__(self, str_to_append):
...         self._appended_str = str_to_append
...         super(AppendedStrCounter, self).__init__()
...     def __setitem__(self, key, value):
...         if len(key) > 1 and not key.endswith(self._appended_str):
...             key += self._appended_str
...         super(AppendedStrCounter, self).__setitem__(tuple(key), value)
... 
>>> AppendedStrCounter('foo bar bar blah'.split())
AppendedStrCounter()

[OUT]：

__init__()

但是from collections import Counter, defaultdict class AppendedStrCounter(Counter): def __init__(self, iter, str_to_append): self._appended_str = str_to_append super(AppendedStrCounter, self).__init__(iter) def __setitem__(self, key, value): if len(key) > 1 and not key.endswith(self._appended_str): key += self._appended_str super(AppendedStrCounter, self).__setitem__(tuple(key), value)的值是错误的，它应该是2而不是1.

使用>>> AppendedStrCounter('foo bar bar blah'.split(), u'\ue000') AppendedStrCounter({('f', 'o', 'o', '\ue000'): 1, ('b', 'a', 'r', '\ue000'): 1, ('b', 'l', 'a', 'h', '\ue000'): 1})以'bar'正确的方式初始化iter？

Answer 1

正如指出的那样 Felix's comment， collections.Counter 没有记录 如何其__init__方法添加键或设置值，只记录它。由于它没有明确地设计用于子类化，最明智的做法是 not 子类化它。

在 collections.abc 模块的存在是为了提供易于子类化的Python内置类型的抽象类，包括dict （MutableMapping，以ABC术语表示）。所以，如果您只需要“Counter - 类” （而不是“Counter的子类，它将满足像isinstance和issubclass这样的内置函数，” 您可以创建自己的MutableMapping，其中包含Counter，然后是“中间人”初始值设定项以及Counter添加到典型dict的三种方法：

import collections import collections.abc def _identity(s): ''' Default mutator function. ''' return s class CustomCounter(collections.abc.MutableMapping): ''' Overrides the 5 methods of a MutableMapping: __getitem__, __setitem__, __delitem__, __iter__, __len__ ...and the 3 non-Mapping methods of Counter: elements, most_common, subtract ''' def __init__(self, values=None, *, mutator=_identity): self._mutator = mutator if values is None: self._counter = collections.Counter() else: values = (self._mutator(v) for v in values) self._counter = collections.Counter(values) return def __getitem__(self, item): return self._counter[self._mutator(item)] def __setitem__(self, item, value): self._counter[self._mutator(item)] = value return def __delitem__(self, item): del self._counter[self._mutator(item)] return def __iter__(self): return iter(self._counter) def __len__(self): return len(self._counter) def __repr__(self): return ''.join([ self.__class__.__name__, '(', repr(dict(self._counter)), ')' ]) def elements(self): return self._counter.elements() def most_common(self, n): return self._counter.most_common(n) def subtract(self, values): if isinstance(values, collections.abc.Mapping): values = {self._mutator(k): v for k, v in values.items()} return self._counter.subtract(values) else: values = (self._mutator(v) for v in values) return self._counter.subtract(values) def main(): def mutator(s): # Asterisks are easier to print than '\ue000'. return '*' + s + '*' words = 'the lazy fox jumps over the brown dog'.split() # Test None (allowed by collections.Counter). ctr_none = CustomCounter(None) assert 0 == len(ctr_none) # Test typical dict and collections.Counter methods. ctr = CustomCounter(words, mutator=mutator) print(ctr) assert 1 == ctr['dog'] assert 2 == ctr['the'] assert 7 == len(ctr) del(ctr['lazy']) assert 6 == len(ctr) ctr.subtract(['jumps', 'dog']) assert 0 == ctr['dog'] assert 6 == len(ctr) ctr.subtract({'the': 5, 'bogus': 100}) assert -3 == ctr['the'] assert -100 == ctr['bogus'] assert 7 == len(ctr) return if "__main__" == __name__: main()

输出（换行，为便于阅读）：

CustomCounter({ '*brown*': 1, '*lazy*': 1, '*the*': 2, '*over*': 1, '*jumps*': 1, '*fox*': 1, '*dog*': 1 })

我在初始化程序mutator中添加了一个仅限关键字的参数，用于存储将真实世界的whatevers转换为“突变”计数版本的函数。请注意，这可能意味着CustomCounter不再存储“可哈希的对象”，而是“不能制作变异器barf的可哈希对象”。

此外，如果标准库的Counter获得了新方法，则必须更新CustomCounter以“覆盖”它们。（你可以通过使用来解决这个问题 __getattr__ 将任何未知属性传递给self._counter，但参数中的任何键都将以原始的“未变异”形式传递给Counter。

最后，正如我之前提到的，如果其他代码专门寻找一个代码，那么实际上不是 collections.Counter的子类。

使用特殊设置功能创建自定义Counter对象

1 个答案: