Python for Everybody
Chapter 11
Exercise 11.1
"""
Exercise 11.1: Write a simple program to simulate the operation of the grep
command on Unix. Ask the user to enter a regular expression and count the
number of lines that matched the regular expression:
$ python grep.py
Enter a regular expression: ^Author
mbox.txt had 1798 lines that matched ^Author
$ python grep.py
Enter a regular expression: ^X-
mbox.txt had 14368 lines that matched ^X-
$ python grep.py
Enter a regular expression: java$
mbox.txt had 4218 lines that matched java$
Python for Everybody: Exploring Data Using Python 3
by Charles R. Severance
Solution by Jamison Lahman, June 4, 2017
"""
import re
count = 0 # Initialize variables
input_exp = input('Enter a regular expression: ')
reg_exp = str(input_exp) # Regular Expressions are strings
fname = 'mbox.txt'
fhand = open(fname)
for line in fhand:
line = line.rstrip()
# Only counts if something was found
if re.findall(reg_exp, line) != []:
count += 1
print(fname + ' had ' + str(count) + ' lines that matched ' + reg_exp)
Exercise 11.2
"""
Exercise 11.2: Write a program to look for lines of the form
'New Revision: 39771'
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.
Enter file:mbox.txt
38549.7949721
Enter file:mbox-short.txt
39756.9259259
Python for Everybody: Exploring Data Using Python 3
by Charles R. Severance
Solution by Jamison Lahman, June 4, 2017
"""
import re
rev = []
fname = input('Enter file: ')
try:
fhand = open(fname)
except FileNotFoundError:
print('File cannot be opened: ', fname)
exit()
for line in fhand:
line = line.rstrip()
rev_temp = re.findall('^New Revision: ([0-9.]+)', line)
if not rev_temp:
for val in rev_temp:
val = float(val) # Convert the strings to floats
rev = rev + [val] # Concats new values
rev_sum = sum(rev)
count = float(len(rev))
rev_ave = rev_sum / count
print(rev_ave)