Chapter 6 Exercise Set 3: mytools

mytools module

Assuming you have configured your development environment as described in Configuring Debian for Python Web Development, create a Python module named seqtools.py in your $HOME/.local/lib/my_python directory. Put the following at the bottom of the module to run doctests:

if __name__ == '__main__':
    import doctest
    doctest.testmod()

Add each of the following functions to your module, making the doctests pass for each one.

reverse(seq)

1. Write a function that reverses its sequence argument, and satisfies these tests

   def reverse(seq):
       """
         >>> reverse('happy')
         'yppah'
         >>> reverse('Python')
         'nohtyP'
         >>> reverse('')
         ''
         >>> reverse('a')
         'a'
         >>> reverse((4, 3, 2, 1))
         (1, 2, 3, 4)
       """
   

mirror(seq)

2. Write a function that mirrors its argument

   def mirror(seq):
       """
         >>> mirror('good')
         'gooddoog'
         >>> mirror('Python')
         'PythonnohtyP'
         >>> mirror('')
         ''
         >>> mirror('a')
         'aa'
         >>> mirror((4, 3, 2, 1))
         (4, 3, 2, 1, 1, 2, 3, 4)
       """
   

remove_element(element, seq)

3. Write a function that removes all occurrences of a given element from a sequence.

   def remove_element(element, seq):
       """
         >>> remove_element('a', 'apple')
         'pple'
         >>> remove_element('a', 'banana')
         'bnn'
         >>> remove_element('z', 'banana')
         'banana'
         >>> remove_element('i', 'Mississippi')
         'Msssspp'
         >>> remove_element('b', '')
         ''
         >>> remove_element(1, (1, 2, 1, 3, 1, 4, 1, 5))
         (2, 3, 4, 5)
       """
   

is_palindrome(seq)

4. Write a function that recognizes palindromes. We will extend the notion of palindrome from strings to sequences in general, calling any sequence that is the same forward and backward a “palindrome”.

   def is_palindrome(seq):
       """
         >>> is_palindrome('abba')
         True
         >>> is_palindrome('abab')
         False
         >>> is_palindrome('tenet')
         True
         >>> is_palindrome('banana')
         False
         >>> is_palindrome('straw warts')
         True
         >>> is_palindrome('a')
         True
         >>> is_palindrome('')
         True
         >>> is_palindrome((1, 2, 2, 1))
         True
         >>> is_palindrome((1, 2, 3, 4))
         False
       """
   

   Hint

   Use your reverse function to make this easy!

count_sub(sub, seq)

5. Write a function that counts how many times a subseq occurs in a sequence.

   def count_sub(sub, seq):
       """
         >>> count_sub('is', 'Mississippi')
         2
         >>> count_sub('an', 'banana')
         2
         >>> count_sub('ana', 'banana')
         2
         >>> count_sub('nana', 'banana')
         1
         >>> count_sub('nanan', 'banana')
         0
         >>> count_sub('aaa', 'aaaaaa')
         4
       """
   

find_sub(sub, seq)

6. Write a function that finds the index of the first occurrence of a substring inside another string. It should return -1 if the substring is not found.

   def find_sub(sub, seq):
       """
         >>> find_sub('an', 'banana')
         1
         >>> find_sub('cyc', 'bicycle')
         2
         >>> find_sub('ud', 'apple strudel')
         9
         >>> find_sub('egg', 'bicycle')
         -1
       """
   

remove_sub(sub, seq)

7. Write a function that removes the first occurrence of a substring from another string.

   def remove_sub(sub, s):
       """
         >>> remove_sub('an', 'banana')
         'bana'
         >>> remove_sub('cyc', 'bicycle')
         'bile'
         >>> remove_sub('iss', 'Mississippi')
         'Missippi'
         >>> remove_sub('egg', 'bicycle')
         'bicycle'
       """
   

   Hint

   One way to write this function would be to call find_sub to get the index of s where sub begins. Then use slicing (see Slices) to take the part before this substring and join it with the part after this substring.

remove_all_sub(sub, seq)

8. Write a function that removes all occurrences of a substring from another string.

   def remove_all_sub(substr, s):
       """
         >>> remove_all_sub('an', 'banana')
         'ba'
         >>> remove_all_sub('cyc', 'bicycle')
         'bile'
         >>> remove_all_sub('iss', 'Mississippi')
         'Mippi'
         >>> remove_all_sub('eggs', 'bicycle')
         'bicycle'
       """
   

   Hint

   This problem can be solved in just a few lines and a simple while loop by calling remove_sub until no changes are made to the string.

remove_punct(s)

9. Write a function that removes all punctuation from a given string.

   def remove_punct(s):
       """
         >>> remove_punct('This... is a "string"; it has, punctuation, yes?')
         'This is a string it has punctuation yes'
         >>> remove_punct('')
         ''
         >>> remove_punct('no punctuation here')
         'no punctuation here'
         >>> remove_punct('$#lots (of?^) punctuation!@# here!**')
         'lots of punctuation here'
       """