Computer Lab 04: strings, tuples, lists

In Lab 04 we will focuse on compound data types which are data types which consist of smaller pieces:

• strings: consists of single characters (strings with length 1)
• tuples: consists of elements which may have different types (integers, strings, floats, tuples etc.)
• lists: typically consists of elements of the same type (all elements are for example integer numbers)

We will practice:

• indexing, slicing
• traversals (for loops, while loops)
• useful methods
• how to work with mutable (lists) and immutable (tuples, strings) data types

• immutable

s = "Hello World"
 
print("indexing:")
print(s[0])
print(s[-1])
print(s[0:5])
print(s[::2])
 
print("\nstring method examples:")
print(s.lower())
print(s.isdecimal())
print(s)
 
print("\nmodifying?:")
s = s[:5] + "_" + s[6:]
print(s)

• immutable
• heterogeneous data structure

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

• mutable
• typically homogenous data structure

def pow2(lst):
	for i in range(len(lst)):
		lst[i] = lst[i]**2
	return lst
 
a = [2,5,6]
b = pow2(a)
print(a)
print(b)

# 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)

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
    """
 
 
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)
    """
 
 
def remove_odd(lst):
    """
    Return a copy of the input list with all odd numbers removed.
 
    :param lst: The input list containing integer numbers
    :return: A new list containing only the even numbers from the original list
    >>> remove_odd([8, 6, 3, 2, 1, 9, 6, 2])
    [8, 6, 2, 6, 2]
    """

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'])
    >>> remove_duplicates([3,2,2,2,1])
    ([3, 2, 1], [2, 2])
    """

• 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.