Python regex char pattern group

Question

I'm trying to do a regex pattern to match all groups of A.. in a string until the next A. (Python)

For example: DFDAXDJSDSJDAFGCJASDJASAGXCJAD into:

'AXDJSDSJD'
'AFGCJ'
'ASDJ'
'AS'
'AGXCJ'
'AD'

The closest thing I came up with was:

string="DFDAXDJSDSJDAFGCJASDJASAGXCJAD"
r=re.compile('(A.[!=A]*)+')
matchObj = r.findall(string, re.M|re.I)

which returns AF, AS, ASA, AD

Why does it skip the first one? Why doesn't it return all chars until the next A?

miku · Accepted Answer · 2013-06-01 16:47:27Z

2

You could just split the string on A:

>>> s = "DFDAXDJSDSJDAFGCJASDJASAGXCJAD"
>>> s.split('A')
['DFD', 'XDJSDSJD', 'FGCJ', 'SDJ', 'S', 'GXCJ', 'D']

# add a leading `A` to each match 'on the fly'
>>> [ 'A%s' % s for s in  s.split('A') ]
['ADFD', 'AXDJSDSJD', 'AFGCJ', 'ASDJ', 'AS', 'AGXCJ', 'AD']

Or use an optional positive lookahead:

>>> re.findall('(A[^A]+(?=A)?)', s, re.IGNORECASE | re.MULTILINE)
['AXDJSDSJD', 'AFGCJ', 'ASDJ', 'AS', 'AGXCJ', 'AD']

Or simply (if you do not care about some next A - which is equivalent to saying that it is optional):

>>> re.findall('(A[^A]+)', s, re.IGNORECASE | re.MULTILINE)
['AXDJSDSJD', 'AFGCJ', 'ASDJ', 'AS', 'AGXCJ', 'AD']

edited Jun 1, 2013 at 16:47

answered Jun 1, 2013 at 13:47

miku

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5 Comments

DSM Over a year ago

The first term isn't a match: ADFD isn't in s.

user2443271 Over a year ago

Thank you, this is probably a different question and a lot more complicated, but what if I wanted to do that for both A and J? Example: 'AXD' 'JSDS' 'JD' ''AFGC' 'J' 'ASD' 'J' 'AS' 'AHXC' 'J' 'AD'

user2443271 Over a year ago

Also, are there some issues with different letters? I tried with different letters and they don't seem to display the same result (only last match/missing first matches)

miku Over a year ago

@user2443271: Here's an example (not sure it is exactly what you want) that would works with two letters: (A[^AJ]+|J[^AJ]+); you can tweak it here: rubular.com/r/64h5ir4YRz

user2443271 Over a year ago

Yes it works. Thank you very much! This one is even more tricky but what if, I wanted to filter the ones where the letter after A or J is an S? The results would be: 'AXD' 'JD' 'AFGC' 'J' 'J' 'AHXC' 'J' 'AD' ('JSDS' 'ASD' and 'AS' would not appear because the second letter is an S)

oleg · Accepted Answer · 2013-06-01 13:51:30Z

2

I can propose following method:

string="DFDAXDJSDSJDAddaFGCJASDJASAGXCJAD"
r=re.compile('A[^A]*', re.I|re.M)
matchObj = r.findall(string)
matchObj

answered Jun 1, 2013 at 13:51

oleg

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