Week 08 Tutorial Questions

Objectives

  1. In assignment 2, you will implement a simple subset of the functionality of the sed command.

    Here are some sed commands and their output.

    Discuss what these print and why:

    quit
    seq 42 44 | sed 1q

    sed 10q < dictionary.txt

    seq 41 43 | sed 4q

    seq 90 110 | sed /.1/q

    sed '/r.*v/q' < dictionary.txt

    yes | sed 3q
    print
    seq 41 43 | sed 2p

    head dictionary.txt | sed 3p

    seq 41 43 | sed -n 2p

    sed -n 42p < dictionary.txt

    head -n 1000 dictionary.txt | sed -n '/z.$/p'
    substitute
    seq 10 15 | sed 's/[15]/zzz/'

    seq 10 15 | sed 's/[15]/zzz/g'

    echo "Hello Andrew" | sed 's/e//'

    echo "Hello Andrew" | sed 's/e//g'
    addresses
    seq 1 5 | sed '$d'

    seq 42 44 | sed 2,3d

    seq 10 21 | sed 3,/2/d

    seq 10 21 | sed /2/,7d

    seq 10 21 | sed /2/,/7/d
    substitute
    seq 1 5 | sed 'sX[15]XzzzX'
    multiple commands
    seq 1 5 | sed '4q;/2/d'
    -f
    echo "4q" > commands.script
echo "/2/d" >> commands.script
seq 1 5 | sed -f commands.script
    input files
    seq 1 2 > two.txt
seq 1 5 > five.txt
sed '4q;/2/d' two.txt five.txt
    whitespace and comments
    seq 24 42 | sed ' 3, 17  d  # comment   ;   /2/p'
    -i
    seq 1 5 > five.txt
sed -i /[24]/d five.txt
cat five.txt
    multiple commands
    echo 'Punctuation characters include . , ; :' | sed 's/;/semicolon/g;/;/q'

  2. What types are available as inbuilt types in Python?

  3. What other useful types are available with Python's standard library?

  4. Write a Python function print_dict() that displays the contents of a dict in the format below: 
    [key] => value
[Andrew] => green
[Anne] => red
[John] => blue
  5. Write a Python program, times.py which prints a table of multiplications.

    Your program will be given the dimensions of the table and the width of the columns to be printed. For example: 

    ./times.py 5 5 5
    1     2     3     4     5
    2     4     6     8    10
    3     6     9    12    15
    4     8    12    16    20
    5    10    15    20    25

    ./times.py 10 10 3
  1   2   3   4   5   6   7   8   9  10
  2   4   6   8  10  12  14  16  18  20
  3   6   9  12  15  18  21  24  27  30
  4   8  12  16  20  24  28  32  36  40
  5  10  15  20  25  30  35  40  45  50
  6  12  18  24  30  36  42  48  54  60
  7  14  21  28  35  42  49  56  63  70
  8  16  24  32  40  48  56  64  72  80
  9  18  27  36  45  54  63  72  81  90
 10  20  30  40  50  60  70  80  90 100

  6. Write a Python program missing_words.py which given two files as arguments prints, in sorted order, all the words found in file1 but not file2.

    You can assume words occur one per line in each file.

  7. Write a Python program source_count.py which prints the number of lines of C source code in the current directory. In other words, this Python program should behave similarly to wc -l *.[ch]. (Note: you are not allowed to use wc or other Unix programs from within the Python script). For example: 

    ./source_count.py
    383 cyclorana.c
    280 cyclorana.h
     15 enum.c
    194 frequency.c
    624 model.c
    293 parse.c
    115 random.c
     51 smooth.c
    132 util.c
     16 util.h
    410 waveform.c
   2513 total

  8. Write a Python program, phone_numbers.py which given the URL of a web page fetches it by running wget and prints any strings that might be phone numbers in the web page.

    Assume the digits of phone numbers may be separated by zero or more spaces or hyphens ('-') and can contain between 8 and 15 digits inclusive.

    You should print the phone numbers one per line with spaces & hyphens removed. 

    ./phone_numbers.py https://www.unsw.edu.au
20151028
11187777
841430912571345
413200225
61293851000
57195873179