Regular Expressions

Task Discussion

• 

  Fer said:

  11th exercises

  http://pastebin.com/FM7eCUbw

  on Nov. 12, 2013, 5:35 a.m.
  
• 

  Wouter Tebbens said:

  The exercises of chapter 11 are here: http://pastebin.com/QM5eqJkh

  on April 7, 2013, 11:03 a.m.
  
• 

  Rob said:

  Chapter 11 Exercises

  on Sept. 29, 2012, 4:29 p.m.
  
• 

  saravanan said:

  Chapter 11

  on Sept. 19, 2012, 9:28 a.m.
  
• 

  Mars83 said:

  My exercises:

  • http://pastebin.com/TTzzzwh7
  • http://pastebin.com/ckL91WZc

  ---

  @Link discussion:

  I would not change the links.

  I think in "Python for Informatics"  you get a first impression of re.search() and re.findall().
  But in "Dive Into Python 3" there are many details not listed in the first source of information.
  For example to set the number of matches with {1, 3} and re.sub().

  on Sept. 11, 2012, 7:52 p.m.
  
• 

  jeroenrijckaert said:

  I've updated the link "Dive Into Python 3" since the old link was broken. It still points to a general page, not a expression-specific. I think it is better to link to http://getpython3.com/diveintopython3/regular-expressions.html.

  Should this be changed? Or just delete the link and use one source of information (Python for Informatics) to keep it simple?

  What do you think?

  on July 16, 2012, 6 a.m.
  
• 

  ionut.vlasin said:

  Exercise 11.1 Write a simple program to simulate the operation of the the grep command on
  UNIX. Ask the user to enter a regular expression and count the number of lines that matched
  the regular expression:

  fhand=open('fis.txt')
  a=raw_input("Please enter the expresion that you want to search in the file: ")
  import re
  count=0
  for line in fhand:
      line=line.rstrip()
      if re.search(a, line):
          count=count+1
  print "we have ",count,"lines which contain",a

  Exercise 11.2 Write a program to look for lines of the form
  New Revision: 39772
  And extract the number from each of the lines using a regular expression and the findall()
  method. Compute the average of the numbers and print out the average.
  import re
  fhand=open('fis1.txt')
  count=0
  _sum=0
  for line in fhand:
      a=re.findall('^N.* R.*: ([0-9].*)',line)
      count=count+1
      _sum=_sum+float(a[0])
  print "Avg=",_sum/count

  on July 11, 2012, 5:45 a.m.
  
• 

  pannix said:

  1. exercise 11.1
  2. exercise 11.2

  on May 25, 2012, 4:33 a.m.
  
• 

  gnuisance said:

  11.1
  11.2

  on March 11, 2012, 5:04 p.m.
  
• 

  RobG717 said:

  Exercise 11.1

  import re
  mbox = open('mbox.txt', 'r')
  
  def grep(expression, file):
      matches = 0
      for line in file:
          line = line.rstrip()
          if re.search(expression, line):
              matches += 1
      return matches
  
  def main():
      """The main program loop"""
      expression = raw_input("Enter a regular expression: ")
      matches = grep(expression, mbox)
      print "mbox.txt had %d lines that matched %s" % (matches, expression)
  
  if __name__ == '__main__':
      main()
  
  

  Exercise 11.2

  import re
  
  def getAverage(filename):
      f = open(filename, 'r')
      matches = []
      for line in f:
          matches.extend(re.findall('^New Revision: (\d+)', line))
      fltmatches = [float(x) for x in matches] #convert values to floats
      average = sum(fltmatches) / len(fltmatches)
      return average
  
  def main():
      """Main program loop"""
      filename = raw_input("Enter file: ")
      average = getAverage(filename)
      print average
  
  if __name__ == '__main__':
      main()

  on Feb. 28, 2012, 5:19 p.m.
  
• 

  Ken Doman said:

  My answers for chapter 11 here.

  on Jan. 17, 2012, 1:42 p.m.
  
• 

  dean said:

  My answers:

  http://goo.gl/xOalm

  on Oct. 12, 2011, 12:53 p.m.
  
• 

  Sudaraka Wijesinghe said:

  My py4int exercise 11 code

  Exercise 11.1

  import re
  
  fname = 'mbox.txt'
  
  rexp = raw_input('Enter a regular expression: ')
  
  try:
      fh=open(fname)
  except:
      print 'Unble to open', fname
      exit()
  
  match_count = 0
  
  for line in fh :
      if re.search(rexp, line) :
          match_count = match_count + 1
  
  print fname, 'had', match_count, 'lines that matched', rexp
  
  

   

  Exercise 11.2

  import re
  
  # Open file get the file name and open it
  fname = raw_input('Enter a file name: ')
  if 1 > len(fname) :
      fname = 'mbox-short.txt'
  
  try:
      fh=open(fname)
  except:
      print 'Unble to open', fname
      exit()
  
  rev_list = []
  
  # Read each line and find out message count for each email address
  for line in fh :
      rev = re.findall('^New Revision: (\d+)', line)
      if 1 > len(rev) :
          continue
  
      rev_list = rev_list + [int(rev[0])]
  
  print 'Average Revision:', sum(rev_list)/len(rev_list)
  
  

  
  

  on July 18, 2011, 3:26 a.m.
  
• 

  Vladimir Támara Patiño said:

  There is a small error in exercise 11.1, the last example says:

  mbox.txt had 4218 lines that matched java$

  But it should be:

  mbox.txt had 4175 lines that matched java$
   

  The official documentation for regular expressions in python is at:

  http://docs.python.org/library/re.html

  11.1

  sre = raw_input('Enter a regular expression: ')
  fname = 'mbox.txt'
  try:
      fhand = open(fname)
  except:
      print 'File cannot be opened:', fname
      exit()
  lm = 0
  for line in fhand:
      n = re.findall(sre, line)
      if len(n) > 0:
          lm = lm + 1
  fhand.close()
  print fname, 'had', lm, 'lines that matched', sre
  

   

  11.2

  fname = raw_input('Enter a file name: ')
  try:
      fhand = open(fname)
  except:
      print 'File cannot be opened:', fname
      exit()
  sum = 0
  num = 0
  for line in fhand:
      n = re.findall(r'\s*New\s+Revision:\s*([0-9]+)', line)
      for i in n:
          sum = sum + int(i)
          num = num + 1
  fhand.close()
  
  if num > 0:
      print 'Average', float(sum)/num
  else:
      print 'Not lines with "New Revision:" found in', fname
  
  

  on June 15, 2011, 8:16 a.m.
  
• 

  Nathan Day said:

  Are there exercises to be released? or are we as a team intended to build our own?

  on June 1, 2011, 4:50 p.m.
  
  

  Tyler Cipriani said:

   

  I took it to mean do the exercises in the course book (Python for Informatics) at the end of the Regex chapter (chapter 11). The other resources listed here are likely for people using different Ptyhon versions than the 2.6/2.7 used in the course text. 

   

  My Chapter 11 exercise answers are posted at https://github.com/thcipriani/thcipriani.github.com/blob/master/python101/chapter11.py for reference

   

  Also, since Regular Expressions are an incredibly dense and useful concept for almost everything you do with coding/computers here is a really helpful tool for learning:

  http://gskinner.com/RegExr/

   

  Making your own exercises might be a cool idea since this is a very dense subject and certainly would help understanding. Trying to parsing out some info from an Apache log file or something similar would be a good exercise.

  on June 2, 2011, 1:36 p.m. in reply to Nathan Day
  
  

  Nathan Day said:

  Would you show me where to find the mbox.txt file and mbox-short.txt file?

  Thanks,

  Nate

  on June 3, 2011, 1:35 p.m. in reply to Tyler Cipriani
  
  

  Tyler Cipriani said:

  Sure - 

  mbox: http://www.py4inf.com/code/mbox.txt

  mbox-short: http://www.py4inf.com/code/mbox-short.txt

  All of the code in the book can be found on the index list at: http://www.py4inf.com/code/

  on June 3, 2011, 1:43 p.m. in reply to Nathan Day
  
  

  Nathan Day said:

  Awesome thanks!

  on June 3, 2011, 2:06 p.m. in reply to Tyler Cipriani