字符串变化 [英] String Variations

问题描述

我在python中有一个字符串和规则"的字典，或者对该字符串的可能更改.例如，一个规则可能具有'he'的键和'e'的值，或者具有'll'的键和'l'的值.

I have a string in python and a dictionary of 'rules', or possible alterations to the string. For example, one rule might have a key of 'he' and a value of 'e', or a key of 'll' and a value of 'l'.

这些规则意味着在我的字符串中出现的任何''he'都可以用'e'替换，对于'll'和'l'类似.

These rules would mean that any occurrence of ``'he' in my string can be replaced with an 'e', and similarly for 'll' and 'l'.

给定这个规则字典，我想要的是找到我的字符串的所有变体.例如，使用上面的两个规则和字符串'hello'，我想返回:

What I want is to find all variations of my string, given this dictionary of rules. For instance, with the two rules from above and the string 'hello', I would like to return:

['hello', 'ello', 'helo', 'elo']

感谢您的帮助，谢谢！

推荐答案

编写一个采用输入子字符串的递归函数.然后，此功能将检查所有规则.对于每个匹配的规则，将进行一次替换，并通过递归调用处理字符串的其余部分:

Write a recursive function that takes a substring of the input. This function then examines all rules. For each rule that matches, one replacement is done, and the remainder of the string is processed by a recursive call:

def apply_rules(rules, input, start=0):
    # First yield the outcome of no applied rules.
    yield input[start:]

    for match, replace in rules:
        # Find the first match for this rule.
        index = input.find(match, start)
        if index < 0:
            # No match -- skip to next one
            continue
        # Prepare the result of the replacement.
        prefix = input[start:index] + replace
        # Apply further rules to the rest of the string
        # by a recursive call.
        for suffix in apply_rules(rules, input, index + len(match)):
            yield prefix + suffix

像这样使用它:

>>> rules = [('he','e'), ('ll','l'), ('e','ee')]
>>> list(apply_rules(rules, 'hello'))
['hello', 'ello', 'elo', 'helo', 'heello', 'heelo']

请注意，我不允许在替换后的字符串上应用规则，以防止出现无限结果的情况，如对该问题的评论中所示.

Please note that I don't allow rules to be applied on replaced strings, to prevent cases of infinite results as demonstrated in the comments to this question.

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