I have a list variable listA as below:

[
'abcd1-2 4d4e',
'xyz0-1 551',
'foo 3ea',
'bar1 2bd',
'mc-mqisd0-2 77a'
]

I need to return a dict out of this list with expanding the digits in the first field. The end result would look like below:

{
abcd1: 4d4e,
abcd2: 4d4e,
xyz0: 551,
xyz1: 551,
foo: 3ea,
bar1: 2bd,
mc-mqisd0: 77a,
mc-mqisd1: 77a,
mc-mqisd2: 77a,
}

I have created below function. It is working with python3 but throwing unmatched group error in some lower python versions.

Anything wrong with the regex here?

  def listFln(listA):
    import re
    fL = []
    for i in listA:
      aL = i.split()[0]
      bL = i.split()[1]
      comp = re.sub('^(. ?)(\d -\d )?$',r'\1',aL)
      cmpCountR = re.sub('^(. ?)(\d -\d )?$',r'\2',aL)
      if cmpCountR.strip():
        nStart = int(cmpCountR.split('-')[0])
        nEnd = int(cmpCountR.split('-')[1])
        for j in range(nStart,nEnd 1):
          fL.append(comp   str(j)   ' '   bL)
      else:
        fL.append(i)

    return(dict([k.split() for k in fL]))

Error:

    cmpCountR = re.sub('^(. ?)(\d -\d )?$',r'\2',aL)
  File "/usr/lib64/python2.7/re.py", line 151, in sub
    return _compile(pattern, flags).sub(repl, string, count)
  File "/usr/lib64/python2.7/re.py", line 275, in filter
    return sre_parse.expand_template(template, match)
  File "/usr/lib64/python2.7/sre_parse.py", line 800, in expand_template
    raise error, "unmatched group"

CodePudding user response：

Here's a simpler version using findall instead of sub, successfully tested on 2,7. It also directly creates the dict instead of first building a list:

mylist=[
'abcd1-2 4d4e',
'xyz0-1 551',
'foo 3ea',
'bar1 2bd',
'mc-mqisd0-2 77a'
]

def listFln(listA):
    import re
    fL = {}
    for i in listA:
        aL = i.split()[0]
        bL = i.split()[1]
        comp = re.findall('^(. ?)(\d -\d )?$',aL)[0]
        if comp[1]:
            nStart = int(comp[1].split('-')[0])
            nEnd = int(comp[1].split('-')[1])
            for j in range(nStart,nEnd 1):
                fL[comp[0] str(j)] = bL
        else:
            fL[comp[0]] = bL
    return fL
    
print(listFln(mylist))
# {'abcd1': '4d4e',
#  'abcd2': '4d4e',
#  'xyz0': '551',
#  'xyz1': '551',
#  'foo': '3ea',
#  'bar1': '2bd',
#  'mc-mqisd0': '77a',
#  'mc-mqisd1': '77a',
#  'mc-mqisd2': '77a'}

CodePudding user response：

Used Python 2.7 to reproduce:

Both patterns compile

import re

# both seem identical
regex1 = '^(. ?)(\d -\d )?$'
regex2 = '^(. ?)(\d -\d )?$'

# also the compiled pattern is identical, see hash
re.compile(regex1)  # <_sre.SRE_Pattern object at 0x7f575ef8fd40>
re.compile(regex2)  # <_sre.SRE_Pattern object at 0x7f575ef8fd40>

Note: The compiled pattern using re.compile() saves time when re-using multiple times like in this loop.

Fix: test for groups found

The error-message indicates that there are groups that aren't matched. Put it other: In the matching result of re.sub (docs to 2.7) there are references to groups like the second capturing group (\2) that have not been found or captured in the given string input:

sre_constants.error: unmatched group

To fix this, we should test on groups that were found in the match. Therefore we use re.match(regex, str) or the compiled variant pattern.match(str) to create a Match object, then Match.groups() to return all found groups as tuple.

import re

regex = '^(. ?)(\d -\d )?$'
pattern = re.compile(regex)  # <_sre.SRE_Pattern object at 0x7f575ef8fd40>


def listFln(listA):
    fL = []
    for i in listA:
        aL = i.split()[0]
        bL = i.split()[1]

        # test for match and groups found
        match = pattern.match(aL)
        print("DEBUG groups:", match.groups())  # tuple containing all the subgroups of the match,
        # watch: the 3 iteration has only group(1)
        
        # break to next iteration here, if no 2nd group
        if not match or not match.group(2):
            continue
            
        comp = re.sub(pattern, r'\1', aL)      
        cmpCountR = re.sub(pattern, r'\2', aL)
        
        if cmpCountR.strip():
            parts = cmpCountR.split('-')
            nStart = int(parts[0])
            nEnd = int(parts[1])
            for j in range(nStart,nEnd 1):
                fL.append(comp   str(j)   ' '   bL)
        else:
            fL.append(i)
        
    return dict([k.split() for k in fL])


listA = [
  'abcd1-2 4d4e',
  'xyz0-1 551',
  'foo 3ea',
  'bar1 2bd',
  'mc-mqisd0-2 77a'
]

as_dict = listFln(listA)
print("resulting dict:", as_dict)

Prints:

('DEBUG groups:', ('abcd', '1-2'))
('DEBUG groups:', ('xyz', '0-1'))
('DEBUG groups:', ('foo', None))
('DEBUG groups:', ('bar1', None))
('DEBUG groups:', ('mc-mqisd', '0-2'))
('resulting dict:', {'mc-mqisd2': '77a', 'mc-mqisd0': '77a', 'mc-mqisd1': '77a', 'xyz1': '551', 'xyz0': '551', 'abcd1': '4d4e', 'abcd2': '4d4e'})