compound regex

spir denis.spir at
Mon Feb 9 15:43:31 EST 2009


(new here)

Below an extension to standard module re. The point is to allow writing and testing sub-expressions individually, then nest them into a super-expression. More or less like using a parser generator -- but keeping regex grammar and power.
I used the format {sub_expr_name}: as in standard regexes {} are only used to express repetition number, a pair of curly braces nesting an identifier should not conflict.

The extension is new, very few tested. I would enjoy comments, critics, etc. I would like to know if you find such a feature useful. You will probably find the code simple enough ;-) 

la vida e estranya

# coding: utf-8

''' 	super_regex
	Define & check sub-patterns individually,
	then include them in global super-pattern.
	uses format {name} for inclusion:
		sub1 = Regex(...)
		sub2 = Regex(...)
		super_format = "...{sub1}...{sub2}..."
		# final regex object:
		super_regex = superRegex(super_format)

from re import compile as Regex

# sub-pattern inclusion format
sub_pattern = Regex(r"{[a-zA-Z_][a-zA-Z_0-9]*}")

# sub-pattern expander
def sub_pattern_expansion(inclusion, dic=None):
	name =[1:-1]
	### namespace dict may be specified -- else globals()
	if dic is None:
		dic = globals()
	if name not in dic:
		raise NameError("Cannot find sub-pattern '%s'." % name)
	return dic[name].pattern

# super-pattern generator
def superRegex(format):
	expanded_format = sub_pattern.sub(sub_pattern_expansion, format)
	return Regex(expanded_format)

if __name__ == "__main__": # purely artificial example use
	# pattern
	time = Regex(r"\d\d:\d\d:\d\d")	# hh:mm:ss
	code = Regex(r"\S{5}")			# non-whitespace x 5
	desc = Regex(r"[\w\s]+$")		# alphanum|space --> EOL
	ref_format = "^ref: {time} #{code} --- {desc}"
	ref_regex = superRegex(ref_format)
	# output
	print 'super pattern:\n"%s" ==>\n"%s"\n' % (ref_format,ref_regex.pattern)
	text = "ref: 12:04:59 #%+.?% --- foo 987 bar"
	result = ref_regex.match(text)
	print 'text: "%s" ==>\n"%s"' %(text,

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