P2PU Python course: exercises chapter 11

'''grep.py'''
"""
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
"""
import re
pattern=raw_input("Enter a regular expression: ")
f=open('mbox.txt')
count=0
for line in f:
    line=line.rstrip()
    if re.search(pattern, line):
        count+=1
print('mbox.txt had %d that matched %s') % (count, pattern)
exit()


'''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
fname = raw_input("Enter a file name: ")
try:
    f = open(fname)
except:
    print "The file %s doesn't exist or could not be opened." % fname
pattern = 'New Revision: ([0-9]+)'
l = list()
for line in f:
    x = re.findall(pattern, line)
    if len(x) > 0:
        l.append(float(x[0]))
print(sum(l) / len(l))
exit()