Match groups in Python

Question

Is there a way in Python to access match groups without explicitly creating a match object  or another way to beautify the example below    Here is an example to clarify my motivation for the question   Following Perl code   if      statement     I love   w         print  He loves  1 n     elsif   statement     Ich liebe   w         print  Er liebt  1 n     elsif   statement     Je t  aime   w         print  Il aime  1 n       translated into Python  m   re search  I love   w     statement  if m    print  He loves  m group 1  else    m   re search  Ich liebe   w     statement    if m      print  Er liebt  m group 1    else      m   re search  Je t aime   w     statement      if m        print  Il aime  m group 1    looks very awkward  if-else-cascade  match object creation

User · Answer

Starting Python 3 8  and the introduction of assignment expressions  PEP 572      operator   we can now capture the condition value re search pattern  statement  in a variable  let s all it match  in order to both check if it s not None and then re-use it within the body of the condition   if match    re search  I love   w     statement     print f He loves  match group 1     elif match    re search  Ich liebe   w     statement     print f Er liebt  match group 1     elif match    re search  Je t aime   w     statement     print f Il aime  match group 1

User · Answer

Less efficient  but simpler-looking   m0   re match  I love   w     statement  m1   re match  Ich liebe   w     statement  m2   re match  Je t aime   w     statement  if m0    print  He loves  m0 group 1  elif m1    print  Er liebt  m1 group 1  elif m2    print  Il aime  m2 group 1    The problem with the Perl stuff is the implicit updating of some hidden variable   That s simply hard to achieve in Python because you need to have an assignment statement to actually update any variables   The version with less repetition  and better efficiency  is this   pats           I love   w      He Loves  0            Ich liebe   w      Er Liebe  0            Je t aime   w      Il aime  0       for p1  p3 in pats      m  re match  p1  statement       if m          print p3 format  m group 1            break   A minor variation that some Perl folk prefer   pats          I love   w       He Loves  0         Ich liebe   w       Er Liebe  0         Je t aime   w       Il aime  0      for p1 in pats      m  re match  p1  statement       if m          print pats p1  format  m group 1            break   This is hardly worth mentioning except it does come up sometimes from Perl programmers

User · Answer

this is not a regex solution   alist   I love     He loves    Je t aime    Il aime   Ich liebe    Er liebt   for k in alist keys        if k in statement         print alist k  statement split k  1

User · Answer

You could create a helper function   def re match group pattern  str  out groups       del out groups        result   re match pattern  str      if result          out groups  len result groups       result groups       return result   And then use it like this   groups      if re match group  I love   w     statement  groups       print  He loves   groups 0  elif re match group  Ich liebe   w     statement  groups       print  Er liebt   groups 0  elif re match group  Je t aime   w     statement  groups       print  Il aime   groups 0    It s a little clunky  but it gets the job done

User · Answer

You could create a little class that returns the boolean result of calling match  and retains the matched groups for subsequent retrieval   import re  class REMatcher object       def   init   self  matchstring           self matchstring   matchstring      def match self regexp           self rematch   re match regexp  self matchstring          return bool self rematch       def group self i           return self rematch group i    for statement in   I love Mary                       Ich liebe Margot                       Je t aime Marie                       Te amo Maria         m   REMatcher statement       if m match r I love   w               print  He loves  m group 1        elif m match r Ich liebe   w              print  Er liebt  m group 1        elif m match r Je t aime   w              print  Il aime  m group 1        else           print         Update for Python 3 print as a function  and Python 3 8 assignment expressions - no need for a REMatcher class now   import re  for statement in   I love Mary                      Ich liebe Margot                      Je t aime Marie                      Te amo Maria         if m    re match r I love   w     statement           print  He loves   m group 1        elif m    re match r Ich liebe   w     statement           print  Er liebt   m group 1        elif m    re match r Je t aime   w     statement           print  Il aime   m group 1        else          print

[python] Match groups in Python

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