Python：如何按短语从右到左拆分字符串（仅限第一次出现）

Question

是否可以在 Python 3 中从右到左（仅第一次出现）拆分短语（可能超过一个单词）上的字符串？

目前我可以根据短语列表拆分字符串，但我有一个极端情况，如果字符串中出现多个指定短语，那么它会同时拆分。

问题

给定一个包含以下内容的示例 CSV：

SENTENCES
THIS IS SENTENCE THREE	1
THIS IS SENTENCE TWO	2
I CONTAIN ONE BUT ALSO TWO	3

我的代码打开一个 CSV，循环遍历每一行，然后拆分指定的短语：

import re
import csv

def split_phrase(string):
    phrases = ['ONE', 'TWO', 'THREE']
    print(f'Raw: {string}')
    split_phrase = '' # Only needed for testing purposes to prevent error on output
    for phrase in phrases:
        if phrase in string:
            list = re.split(f'\\b({phrase})\\b', string)
            print(f'Split: {list}')
            sentence = list[0]
            split_phrase = list[1]
            print(f'Phrase: {split_phrase}')

    return sentence, split_phrase

input_dir = 'input1/'
output_dir = 'output1/'
filename = 'demo.csv'

with open(input_dir + filename, 'r') as input_csv:
    csv_reader = csv.reader(input_csv)
    data = list(csv_reader)
    input_csv.close()

    for row in data[1:]: # Ignore the header row
        sentence = row[0] # First column
        sentence = split_phrase(sentence) # Split out specified phrase

我得到以下输出：

$ python3 demo.py
Raw: THIS IS SENTENCE THREE
Split: ['THIS IS SENTENCE ', 'THREE', '']
Phrase: THREE
Raw: THIS IS SENTENCE TWO
Split: ['THIS IS SENTENCE ', 'TWO', '']
Phrase: TWO
Raw: I CONTAIN ONE BUT ALSO TWO
Split: ['I CONTAIN ', 'ONE', ' BUT ALSO TWO']
Phrase: ONE
Split: ['I CONTAIN ONE BUT ALSO ', 'TWO', '']
Phrase: TWO

注意：最后一个句子由 for 循环处理两次，因为它包含短语列表中的两个短语。

期望的结果

我知道在列出的要拆分的短语中，它始终是右侧的最后一个。所以我想只从右到左抓取第一个匹配项。

注意：“短语”可以包含一个或多个单词。

这可能吗？如果是这样，我该如何实现？

Answer 1

我已通过使用string.rfind() 从字符串末尾搜索并遍历可能的短语列表来回答这个问题。可能有更好的不重复的方法，但这是我发现的最好的。

one = "THIS IS SENTENCE THREE"
two = "THIS IS SENTENCE TWO"
three = "I CONTAIN ONE BUT ALSO TWO"
four = "I CONTAIN ONE BUT ALSO TWO AND SOME MORE TEXT"
phrases = ['ONE', 'TWO', 'THREE']

def find_words(phrases, string):
    i = -1
    p = ""
    for phrase in phrases:
        newI = string.rfind(phrase)
        if newI > i:
            i = newI
            p = phrase
    return (string[:i], string[i:i+len(p)], string[i+len(p)::])

print(find_words(phrases, one))
print(find_words(phrases, two))
print(find_words(phrases, three))
print(find_words(phrases, four))

输出：

('THIS IS SENTENCE ', 'THREE', '')
('THIS IS SENTENCE ', 'TWO', '')
('I CONTAIN ONE BUT ALSO ', 'TWO', '')
('I CONTAIN ONE BUT ALSO ', 'TWO', ' AND SOME MORE TEXT')

Answer 2

我相信如果你使用“rsplit()”而不是“split()”，它会起作用

Answer 3

我认为关键是拆分成单词，然后反转该列表，然后搜索所有命中并选择最小的数字：

def split_word(string):
    words = ['ONE', 'TWO', 'THREE']
    search = string.split()
    rsearch = list(reversed(search))
    locs = [rsearch.index(w) for w in words if w in rsearch]
    if not locs:
        return None
    target = len(search) - min(locs) - 1
    return ' '.join(search[0:target]), search[target], ' '.join(search[target+1:])

print(split_word("THIS IS SENTENCE THREE"))
print(split_word("THIS IS SENTENCE TWO"))
print(split_word("I CONTAIN ONE BUT ALSO TWO"))

输出：

('THIS IS SENTENCE', 'THREE', '')
('THIS IS SENTENCE', 'TWO', '')
('I CONTAIN ONE BUT ALSO', 'TWO', '')