gry wrote:
[ python3.1.1, re.__version__='2.2.1' ]
I'm trying to use re to split a string into (any number of) pieces of
these kinds:
1) contiguous runs of letters
2) contiguous runs of digits
3) single other characters
e.g. 555tHe-rain.in#=1234 should give: [555, 'tHe', '-', 'rain',
'.', 'in', '#', '=', 1234]
I tried:
re.match('^(([A-Za-z]+)|([0-9]+)|([-.#=]))+$', '555tHe-rain.in#=1234').groups()
('1234', 'in', '1234', '=')
Why is 1234 repeated in two groups? and why doesn't "tHe" appear as a
group? Is my regexp illegal somehow and confusing the engine?
I *would* like to understand what's wrong with this regex, though if
someone has a neat other way to do the above task, I'm also interested
in suggestions.
If the regex was illegal then it would raise an exception. It's doing
exactly what you're asking it to do!
First of all, there are 4 groups, with group 1 containing groups 2..4 as
alternatives, so group 1 will match whatever groups 2..4 match:
Group 1: (([A-Za-z]+)|([0-9]+)|([-.#=]))
Group 2: ([A-Za-z]+)
Group 3: ([0-9]+)
Group 4: ([-.#=])
It matches like this:
Group 1 and group 3 match '555'.
Group 1 and group 2 match 'tHe'.
Group 1 and group 4 match '-'.
Group 1 and group 2 match 'rain'.
Group 1 and group 4 match '.'.
Group 1 and group 2 match 'in'.
Group 1 and group 4 match '#'.
Group 1 and group 4 match '='.
Group 1 and group 3 match '1234'.
If a group matches then any earlier match of that group is discarded,
so:
Group 1 finishes with '1234'.
Group 2 finishes with 'in'.
Group 3 finishes with '1234'.
Group 4 finishes with '='.
A solution is:
>>> re.findall('[A-Za-z]+|[0-9]+|[-.#=]', '555tHe-rain.in#=1234')
['555', 'tHe', '-', 'rain', '.', 'in', '#', '=', '1234']
Note: re.findall() returns a list of matches, so if the regex doesn't
contain any groups then it returns the matched substrings. Compare:
>>> re.findall("a(.)", "ax ay")
['x', 'y']
>>> re.findall("a.", "ax ay")
['ax', 'ay']
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