I have a form field, that most contain only inline ordered list:
1. This item may be contain characters, symbols or numbers. 2. And this item also...
The following code not working for user input validation (users can input only inline ordered list):
definiton_re = re.compile(r'^(?:\d\.\s(?:.+?))+$')
validate_definiton = RegexValidator(definiton_re, _("Enter a valid 'definition' in format: 1. meaning #1, 2. meaning #2...etc"), 'invalid')
PS: Here i'm using RegexValidator class from Django framework to validate form field value.
Here is my solution. It's working not bad.
input = '1. List item #1, 2. List item 2, 3. List item #3.'
regex = re.compile(r'(?:^|\s)(?:\d{1,2}\.\s)(.+?)(?=(?:, \d{1,2}\.)|$)')
# Parsing.
regex.findall(input) # Result: ['List item #1', 'List item 2', 'List item #3.']
# Validation.
validate_input = RegexValidator(regex, _("Input must be in format: 1. any thing..., 2. any thing...etc"), 'invalid')
validate_input(input) # No errors.
Nice solution from OP. To push it further, let's do some regex optimization / golfing.
(?<!\S)\d{1,2}\.\s((?:(?!,\s\d{1,2}\.),?[^,]*)+)
Here's what's new:
(?:^|\\s)
Matches with backtracking between the alternation. Here we use (?<!\\S)
instead, to assert that we're not in front of a non-whitespace character.\\d{1,2}\\.\\s
doesn't have to be within a non-capturing group. (.+?)(?=(?:, \\d{1,2}\\.)|$)
is too bulky. We change this bit to:
(
Capturing group (?:
(?!
Negative lookahead: Assert that our position is NOT : ,\\s\\d{1,2}\\.
A comma, whitespace character, then a list index.)
,?[^,]*
Here's the interesting optimization: *
quantifier, and there's no backtracking.(.+?)
.)+
Keep repeating the group until the negative lookahead assertion fails. )
You can use that in place of the regex in the other answer , and here's a regex demo !
Though, at first glance, this problem is better solved with re.split()
while parsing:
input = '1. List item #1, 2. List item 2, 3. List item #3.';
lines = re.split('(?:^|, )\d{1,2}\. ', input);
# Gives ['', 'List item #1', 'List item 2', 'List item #3.']
if lines[0] == '':
lines = lines[1:];
# Throws away the first empty element from splitting.
print lines;
Here is an online code demo .
Unfortunately, for the validation you would have to follow the regex matching approach, just compile the regex upstairs:
regex = re.compile(r'(?<!\S)\d{1,2}\.\s((?:(?!,\s\d{1,2}\.),?[^,]*)+)')
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