Python - regular expression backreference example

# use the power of regular expressions
# bite the bullet and review the regular expression syntax 

import re

# lets say you have created the next search engine
# your search engine extracts the contents of
# the <title></title> tags
theString = """ <lots of garbage and # what not and this

title is going to be cool> <myTitle> will be awesome.
And once you get <title>the title is here</title> and then
there is the end """

# you compile a regular expression to search

# for the contents of the title tag
# (this is where the regular expression syntax http://docs.python.org/library/re.html#regular-expression-syntax
# comes in handy)
# the one thing to certainly notice is that there are
# parenthesis surrounding the contents of the title tag.
# These are called backreferences.  Once we've run the search
# we'll be able to reference these.
p = re.compile('<title>(.+)<\/title>')


# now search theString
m = re.search(p, theString)

# you can test whether or not your
# regular expression was successfull
if m:
    print "regular expression search successfull!"
    # referencing group #1 references the first backreference

    print "the title contents are:", m.group(1)
    # group # 0 is the entire regular expression result
    print "the entire regular expression returned:", m.group(0)

else:
    print "regular expression search returns no results"

#output:
#   regular expression search successfull!
#   the title contents are: the title is here
#   the entire regular expression returned: <title>the title is here</title>

Python - simple regular expression examples

# regular expressions are extremely powerful
# here are some simple examples to get you started

import re

text = "Some example text to manipulate with regular expressions."

# find the location of all the vowels
# iterate through all vowels
# here I've used the finditer method to return and
#   and iterator through the results
for i in re.finditer('[aeiouy]', text):
    print "location:", i.start(), " to ", i.end()
    print "  found text was: ", text[i.start():i.end()]
# output:
#location: 1  to  2
#  found text was:  o
#location: 3  to  4
#  found text was:  e
#
# SNIP -- there are lots of vowels
#
#location: 49  to  50
#  found text was:  e
#location: 52  to  53
#  found text was:  i
#location: 53  to  54
#  found text was:  o

# use regular expressions to split your sentence into words
sentence = "This is my example sentence"
for word in re.split(' ', sentence):
    print word
#Output:
# This
# is
# my
# example
# sentence

# search and replace regular expression functionality
# replace 'regular expression' with 're'
text = "regular expression text goes here"
newText = re.sub('regular expression', 're', text)
print newText
#Outputs:
# re text goes here

python - split paragraph into sentences with regular expressions

# split up a paragraph into sentences
# using regular expressions


def splitParagraphIntoSentences(paragraph):
    ''' break a paragraph into sentences
        and return a list '''
    import re
    # to split by multile characters

    #   regular expressions are easiest (and fastest)
    sentenceEnders = re.compile('[.!?]')
    sentenceList = sentenceEnders.split(paragraph)
    return sentenceList


if __name__ == '__main__':
    p = """This is a sentence.  This is an excited sentence! And do you think this is a question?"""

    sentences = splitParagraphIntoSentences(p)
    for s in sentences:
        print s.strip()

#output:
#   This is a sentence
#   This is an excited sentence

#   And do you think this is a question