python - 正则表达式表现出意外

Question

脚本:

import re

matches = ['hello', 'hey', 'hi', 'hiya']

def check_match(string):
    for item in matches:
        if re.search(item, string):
            print 'Match found: ' + string
        else:
            print 'Match not found: ' + string

check_match('hey')
check_match('hello there')
check_match('this should not match')
check_match('oh, hiya')

输出:

Match not found: hey
Match found: hey
Match not found: hey
Match not found: hey
Match found: hello there
Match not found: hello there
Match not found: hello there
Match not found: hello there
Match not found: this should not match
Match not found: this should not match
Match found: this should not match
Match not found: this should not match
Match not found: oh, hiya
Match not found: oh, hiya
Match found: oh, hiya
Match found: oh, hiya

有很多我不明白的地方，对于初学者来说，每个字符串在这个输出中被搜索了四次，有的返回两次作为找到的匹配项，有的返回 3 次。我不确定我的代码中有什么问题导致了这种情况发生，但有人可以尝试看看问题出在哪里吗？

预期的输出是这样的:

Match found: hey
Match found: hello there
Match not found: this should not match
Match found: oh, hiya

Answer 1

这不是行为不正确，而是你对 re.search(...) 的误解。

查看输出后的评论:

Match not found: hey                    # because 'hello' is not in 'hey'
Match found: hey                        # because 'hey' is in 'hey'
Match not found: hey                    # because 'hi' is not in 'hey'
Match not found: hey                    # because 'hiya' is not in 'hey'

Match found: hello there                # because 'hello' is in 'hello there'
Match not found: hello there            # because 'hey' is not in 'hello there'
Match not found: hello there            # because 'hi' is not in 'hello there'
Match not found: hello there            # because 'hiya' is not in 'hello there'

Match not found: this should not match  # because 'hello' is not in 'this should not match'
Match not found: this should not match  # because 'hey' is not in 'this should not match'
Match found: this should not match      # because 'hi' is in 'this should not match'
Match not found: this should not match  # because 'hiya' is not in 'this should not match'

Match not found: oh, hiya               # because 'hello' is not in 'oh, hiya'
Match not found: oh, hiya               # because 'hey' is not in 'oh, hiya'
Match found: oh, hiya                   # because 'hi' is in 'oh, hiya'
Match found: oh, hiya                   # because 'hiya' is in 'oh, hiya'

如果您不想在输入oh, hiya 时匹配模式hi，您应该将单词边界环绕在您的模式周围:

\bhi\b

这将导致它只匹配出现的 hi not 被其他字母包围(well hiya there不会匹配模式\bhi\b，但是你好会)。