Python parsing list of string

Question

I have list of strings, I'm looking for lines like this:

Key: af12d9 Index: 0 Field 1: 1234 Field 2: 1234 Field 3: -10

after finding lines like this, I want to store each one as a dictionary {'key' : af12d9, 'index' : 0, 'field 1' : .... }, then store this dictionary to a list, so I will have a list of dictionaries.

I was able to get it working like this:

listconfig = []
for line in list_of_strings:
    matched = findall("(Key:[\s]*[0-9A-Fa-f]+[\s]*)|(Index:[\s]*[0-9]+[\s]*)|(Field 1:[\s]*[0-9]+[\s]*)|(Field 2:[\s]*[0-9]+[\s]*)|(Field 3:[\s]*[-+]?[0-9]+[\s]*)", line)
    if matched:
        listconfig += [dict(map(lambda pair: (pair[0].strip().lower(), pair[1].strip().lower()),
                                map(lambda line: line[0].split(':'),
                                    [filter(lambda x: x, group) for group in matched])))]

I'm just wondering if there could a better way (short and efficient) to do this because I think the findall will do 5 searches per string. (correct? since it returns a list of 5 tuples.)

Thank you.

Solution:

OK, with help of brandizzi, I have found THE answer to this question.

Solution:

listconfig = []
for line in list_of_strings:
    matched = re.search(r"Key:[\s]*(?P<key>[0-9A-Fa-f]+)[\s]*" \ 
                        r"(Index:[\s]*(?P<index>[0-9]+)[\s]*)?" \ 
                        r"(Field 1:[\s]*(?P<field_1>[0-9]+)[\s]*)?" \ 
                        r"(Field 2:[\s]*(?P<field_2>[0-9 A-Za-z]+)[\s]*)?" \ 
                        r"(Field 3:[\s]*(?P<field_3>[-+]?[0-9]+)[\s]*)?", line) 
    if matched:
        print matched.groupdict()
        listconfig.append(matched.groupdict())

Solution 1

OK, with help of brandizzi, I have found THE answer to this question.

Solution:

listconfig = []
for line in list_of_strings:
    matched = re.search(r"Key:[\s]*(?P<key>[0-9A-Fa-f]+)[\s]*" \ 
                        r"(Index:[\s]*(?P<index>[0-9]+)[\s]*)?" \ 
                        r"(Field 1:[\s]*(?P<field_1>[0-9]+)[\s]*)?" \ 
                        r"(Field 2:[\s]*(?P<field_2>[0-9 A-Za-z]+)[\s]*)?" \ 
                        r"(Field 3:[\s]*(?P<field_3>[-+]?[0-9]+)[\s]*)?", line) 
    if matched:
        print matched.groupdict()
        listconfig.append(matched.groupdict())

Solution 2

Firstly, your regex seems to not work properly. The Key field should have values which could include f, right? So its group should not be ([0-9A-Ea-e]+) but instead ([0-9A-Fa-f]+). Also, it is a good - actually, a wonderful - practice to prefix the regex string with r when dealing with regexes because it avoids problems with \ escaping characters. (If you do not understand why to do it, look at raw strings)

Now, my approach to the problem. First, I would create a regex without pipes:

>>> regex = r"(Key):[\s]*([0-9A-Fa-f]+)[\s]*" \
...     r"(Index):[\s]*([0-9]+)[\s]*" \
...     r"(Field 1):[\s]*([0-9]+)[\s]*" \
...     r"(Field 2):[\s]*([0-9 A-Za-z]+)[\s]*" \
...     r"(Field 3):[\s]*([-+]?[0-9]+)[\s]*"

With this change, the findall() will return only one tuple of found groups for an entire line. In this tuple, each key is followed by its value:

>>> re.findall(regex, line)
[('Key', 'af12d9', 'Index', '0', 'Field 1', '1234', 'Field 2', '1234 Ring ', 'Field 3', '-10')]

So I get the tuple...

>>> found = re.findall(regex, line)[0]
>>> found
('Key', 'af12d9', 'Index', '0', 'Field 1', '1234', 'Field 2', '1234 Ring ', 'Field 3', '-10')

...and using slices I get only the keys...

>>> found[::2]
('Key', 'Index', 'Field 1', 'Field 2', 'Field 3')

...and also only the values:

>>> found[1::2]
('af12d9', '0', '1234', '1234 Ring ', '-10')

Then I create a list of tuples containing the key and its corresponding value with zip() function:

>>> zip(found[::2], found[1::2])
[('Key', 'af12d9'), ('Index', '0'), ('Field 1', '1234'), ('Field 2', '1234 Ring '), ('Field 3', '-10')]

The gran finale is to pass the list of tuples to the dict() constructor:

>>> dict(zip(found[::2], found[1::2]))
{'Field 3': '-10', 'Index': '0', 'Field 1': '1234', 'Key': 'af12d9', 'Field 2': '1234 Ring '}

I find this solution the best, but it is indeed a subjective question in some sense. HTH anyway :)