Computer Lab 04, strings, tuples, lists

complex data types: strings, tuples, lists. Traversing. Basic methods.

implement the following functions and test them appropriately.

def count_chars(string, char):
    """Return the number of occurances of char in string.
 
    :param string: a string. Example "hello world"
    :param char: character. Example "l"
    :return: int number of char occurences in string
    >>> count_chars("hello","l")
    2
    """

def replace_chars(string, char_original, char_replacement):
    """Return a new string with all occurences of char_original replaced by char_replacement.
 
    :param string: string in which some chars shall be replaced
    :param char_original: character to be replaced
    :param char_replacement: character to be inserted instead of char_original
    :return: a new string with replaced characters
    >>> replace_chars("hello","h","H")
    'Hello'
    """

def reverse_string(string):
    """Return a reversed version of string.
 
    :param string: string to be reversed
    :return: reversed string
    >>> reverse_string("hello")
    'olleh'
    """

def is_palindrom(string):
    """Return True if and only if the string is equal to its reversed version.
 
    :param string: string to check for palindrom
    :return: boolean
    >>> is_palindrom("aka")
    True
    >>> is_palindrom("hello")
    False
    """

• immutable
• heterogeneous data structure

# packing
b = ("Bob", 19, "CS")
 
#unpacking
(name, age, studies) = b
name
age
studies

def circle_chars(radius):
    """Return a circumference and an area of a circle.
 
    :param radius: int radius of a circle.
    :return: (int, int) tuple containing circumference and area (in this order)
    >>> circle_chars(3)
    (18.84955592153876, 28.274333882308138)
    """

# Wentworth (2012)
students = [
    ("John", ["CompSci", "Physics"]),
    ("Vusi", ["Maths", "CompSci", "Stats"]),
    ("Jess", ["CompSci", "Accounting", "Economics", "Management"]),
    ("Sarah", ["InfSys", "Accounting", "Economics", "CommLaw"]),
    ("Zuki", ["Sociology", "Economics", "Law", "Stats", "Music"])]
 
# Count how many students are taking CompSci
counter = 0
for (name, subjects) in students:
    if "CompSci" in subjects:
           counter += 1
 
print("The number of students taking CompSci is", counter)

Required filename: 04_weekly_hw.py.

def remove_duplicates(items):
    """Remove duplicate items.
 
    :param items: input list, can contain anything
    :return: (unique_list, duplicates)
        unique_list - a list with unique items only
        duplicates - a list with items that were in items more than once (not unique list)
    >>> remove_duplicates(['h','e','l','l','o'])
    (['h', 'e', 'l', 'o'], ['l'])
    """

• The homework from last week was to read chapters 6,7,8,9 from Wentworth2012. Go through them once more and concentrate on things you do not understand.
• Read chapter 11 (Lists) from Wentworth2012.