正则表达式用于多行字符串？

Question

I have the following input:

str = """

    Q: What is a good way of achieving this?

    A: I am not sure. Try the following:

    1. Take this first step. Execute everything.

    2. Then, do the second step

    3. And finally, do the last one



    Q: What is another way of achieving this?

    A: I am not sure. Try the following alternatives:

    1. Take this first step from before. Execute everything.

    2. Then, don't do the second step

    3. Do the last one and then execute the above step

"""

I want to capture the QA pairs in the input but I am not able to get a good regex to do this. I managed the following:

(?ms)^[\s#\-\*]*(?:Q)\s*:\s*(\S.*?\?)[\s#\-\*]+(?:A)\s*:\s*(\S.*)$

But, I'm able to capture the input as follows:

('Q', 'What is a good way of achieving this?')
('A', "I am not sure. Try the following:\n    1. Take this first step. Execute everything.\n    2. Then, do the second step\n    3. And finally, do the last one\n\n    Q: What is another way of achieving this?\n    A: I am not sure. Try the following alternatives:\n    1. Take this first step from before. Execute everything.\n    2. Then, don't do the second step\n    3. Do the last one and then execute the above step\n")

Notice how the second QA pair got captured by the first. If I use a greedy ? at the end of the answer regex, it does not capture the enumerations. Any suggestions on how to solve this?

Answer 1

解决问题的一种惰性方法，但不是最好的方法，是用“ Q：”将字符串炸开，然后用简单的/Q:(.+)A:(.+)/msU（通常为正则表达式）解析这些部分。 。

Answer 2

Just using this works fine for me. Only requires trimming a bit of whitespace.

(?s)(Q):((?:(?!A:).)*)(A):((?:(?!Q:).)*)

Example of use:

>>> import re
>>> str = """
...
...     Q: What is a good way of achieving this?
...
...     A: I am not sure. Try the following:
...
...     1. Take this first step. Execute everything.
...
...     2. Then, do the second step
...
...     3. And finally, do the last one  ...      ...   ...
...     Q: What is another way of achieving this?
...
...     A: I am not sure. Try the following alternatives:
...
...     1. Take this first step from before. Execute everything.
...
...     2. Then, don't do the second step
...
...     3. Do the last one and then execute the above step
...
... """
>>> regex = r"(?s)(Q):((?:(?!A:).)*)(A):((?:(?!Q:).)*)"
>>> match = re.findall(regex, str)
>>> map(lambda x: [part.strip().replace('\n', '') for part in x], match)
[['Q', 'What is a good way of achieving this?', 'A', 'I am not sure. Try the following:    1. Take this first step. Execute everything.    2. Then, do the second step    3. And finally, do the last one'], ['Q', 'What is another way of achieving this?', 'A', "I am not sure. Try the following alternatives:    1. Take this first step from before. Execute everything.    2. Then, don't do the second step    3. Do the last one and then execute the above step"]]

Even added a little thingie to help you clean the whitespaces at the end there.

Answer 3

I'm not that smart to write huge regex(yet), so here is my non-regex solution -

>>> str = """

    Q: What is a good way of achieving this?

    A: I am not sure. Try the following:

    1. Take this first step. Execute everything.

    2. Then, do the second step

    3. And finally, do the last one



    Q: What is another way of achieving this?

    A: I am not sure. Try the following alternatives:

    1. Take this first step from before. Execute everything.

    2. Then, don't do the second step

    3. Do the last one and then execute the above step

"""
>>> qas = str.strip().split('Q:')
>>> clean_qas = map(lambda x: x.strip().split('A:'), filter(None, qas))
>>> print clean_qas
[['What is a good way of achieving this?\n\n    ', ' I am not sure. Try the following:\n\n    1. Take this first step. Execute everything.\n\n    2. Then, d
o the second step\n\n    3. And finally, do the last one'], ['What is another way of achieving this?\n\n    ', " I am not sure. Try the following alternativ
es:\n\n    1. Take this first step from before. Execute everything.\n\n    2. Then, don't do the second step\n\n    3. Do the last one and then execute the
above step"]]

You should clean the whitespaces though. Or you could do what Puciek said.

Just for fun -

>>> clean_qas = map(lambda x: map(lambda s: s.strip(), x.strip().split('A:')), filter(None, qas))
>>> print clean_qas
[['What is a good way of achieving this?', 'I am not sure. Try the following:\n\n    1. Take this first step. Execute everything.\n\n    2. Then, do the sec
ond step\n\n    3. And finally, do the last one'], ['What is another way of achieving this?', "I am not sure. Try the following alternatives:\n\n    1. Take
 this first step from before. Execute everything.\n\n    2. Then, don't do the second step\n\n    3. Do the last one and then execute the above step"]]

Looks ugly though.

Answer 4

Slightly modifying your original solution:

(?ms)^[\s#\-\*]*(?:Q)\s*:\s+(\S[^\n\r]*\?)[\s#\-\*]+(?:A)\s*:\s+(\S.*?)\s*(?=$|Q\s*:\s+)

• Questions and answers must have at least one space after the : .
• Instead of matching questions non-greedily (which won't allow for having multiple ? 's in one question), don't allow newlines in questions.
• Instead of matching to end of string, non-greedily match until either the match is followed by the end of the string or it's followed by another question.

Use re.findall to get all question/answer matches.