Monday, October 22, 2012

String pattern matching in Java and Python

I needed to extract substring: the input is
rename_method("%.Arith#add()","%.Arith#addRefactored()","%.Arith")
And from the string I need to extract the substrings in the quotation marks:
%.Arith#add(), %.Arith#addRefactored(), %.Arith
The java code could be implemented as:
  Pattern p = Pattern.compile("rename_method\\(" + // ignore 'rename_method('
    "\"([^\"]*)\"," +                        // find '"....",'
    "\"([^\"]*)\"," +
    "\"([^\"]*)\""  +
    "\\)");                                  // ignore closing ')'
  Matcher m = p.matcher(refactoring);
  
  boolean result = m.find();
  if (result)
  {
   beforeMethodName = m.group(1);
   afterMethodName = m.group(2);
  }
Python uses some interesting features to make the code simpler and easier to read.
matchstring = (
"rename_method\("   # 
  "\"([^\"]*)\","  # %.Arith#add()
  "\"([^\"]*)\","  # %.Arith#addRefactored()
  "\"([^\"]*)\""   # %.Arith
  "\)"
)
inputstring = r'rename_method("%.Arith#add()","%.Arith#addRefactored()","%.Arith")';

m = re.search(matchstring, inputstring)
print m
if m:
 beforeMethodName = m.group(1)
 afterMethodName = m.group(2)
You can use python re module's compile/match, and by doing so, you can remove bunch of parenthesis
p = re.compile(r"""
rename_method\(   # 
  \"([^\"]*)\",   # %.Arith#add()
  \"([^\"]*)\",   # %.Arith#addRefactored()
  \"([^\"]*)\"    # %.Arith
  \)
"""
, re.VERBOSE)

m = p.match(inputstring)
if m:
 beforeMethodName = m.group(1)
 afterMethodName = m.group(2)
For concatenating strings in python with some comment, you can check this post. For re.VERBOSE, check this site. For regular expression in python, check this site, and this one.

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