可以将正则表达式用作字典中的键吗? [英] Can a regular expression be used as a key in a dictionary?

问题描述

我想创建一个字典，其中的键是正则表达式:

I want to create a dictionary where the keys are regular expressions:

d = {'a.*': some_value1, 'b.*': some_value2}

然后，当我查看字典时:

Then, when I look into the dictionary:

d['apple']

我希望苹果'apple'与作为正则表达式的键匹配.如果与key/regular-expression完全匹配，则应返回相应的值.

I want apple 'apple' to be matched against the keys which are regular expressions. If there is a complete match with a key/regular-expression then the corresponding value should be returned.

例如'apple'与正则表达式'a.*'完全匹配，因此，应返回some_value1.

For example 'apple' matches with the regular expression 'a.*' completely, and so, some_value1 should be returned.

当然，所有这一切都假定正则表达式键不冲突(即，两个键不应都完全匹配相同的字符串).假设我在构建密钥时可以手动满足此要求.

Of course, all of this assumes that the regular expression keys do not conflict (i.e. two keys should not both match the same string exactly). Let's say I can manually take care of this requirement when building my keys.

这在Python中可行吗?如果是这样，那将是一个相当优雅而强大的构造！

Is this possible in Python? If so, it would be quite an elegant and powerful construct!

推荐答案

Python字典实现为哈希表-这意味着通过内部散列myvalue来进行任何mydict[myvalue]查找都非常快.使用正则表达式作为键将取消此功能.而不是使用字典，您应该使用简单的列表或元组，其中每个项目都是格式为(pattern/compiled regular expression, value)的元组，并对其进行扫描，直到通过正则表达式为止.这也使您能够按正则表达式的顺序进行操作(例如，从特定到通用):

Python dictionaries are implemented as hash tables - which means any mydict[myvalue] lookup is very fast by internally hashing myvalue. Using regular expressions as keys will cancel this functionality. Instead of using a dictionary, you should use a simple list or tuple where each item is a tuple in the format: (pattern/compiled regular expression, value) and scan them until a regular expression passes. This will also give you the ability to play with the order of regular expressions (from specific to general, for example):

import re

LOOKUPS  = [
    ('a.*', 'a'),
    ('b.*', 'b'),
]

def lookup(s, lookups):
    for pattern, value in lookups:
        if re.search(pattern, s):
            return value
    return None

print(lookup("apple", LOOKUPS))

另请参阅Django的 URL解析器(非常)高级实施您的想法.

See also Django's url resolver for a (very) advanced implementation of your idea.

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