Contents

• 3. Working with data collections
  • 3.1 Lists
  • 3.2 Tuples
  • 3.3 Sets
  • 3.4 Dictionaries

3.1 Lists

• A list groups multiple data items in 1 column.\
• A list starts and ends with [ ] and can contain different data types. (Data types are covered in more detail in the next section.)

list_mixed = [0, 2.5, 'abc']

• Lists can be created in various ways, as shown below.

# Create an empty list
empty_list = []
print(empty_list)

[]

# Create by entering values directly
list_manual = [0, 1, 2, 3, 4]
print(list_manual)

[0, 1, 2, 3, 4]

# Create using range (A, B, C below are all integers)
# range(B) - create a list from 0 in steps of 1 up to integers less than B
list_new = list(range(10))
print(list_new)

# range(A,B) - create a list starting at A in steps of 1 up to integers less than B
list_new = list(range(1,10))
print(list_new)

# range(A,B,C) - create a list starting at A in steps of C up to integers less than B (reverse for negative C)
list_new = list(range(2,10,2))
print(list_new)

[0, 1, 2, 3, 4, 5, 6, 7, 8, 9]
[1, 2, 3, 4, 5, 6, 7, 8, 9]
[2, 4, 6, 8]

• The + and * operations behave somewhat differently for lists.
  • The + operation concatenates the lists on its left and right.
  • The * operation repeats the list to the left of * the number of times specified on the right.

# + and * operations on lists
list_manual = [0, 1, 2, 3, 4]
list_new = list(range(4,-1,-1))
print(list_manual+list_new)
print(list_manual*2)

[0, 1, 2, 3, 4, 4, 3, 2, 1, 0]
[0, 1, 2, 3, 4, 0, 1, 2, 3, 4]

• Lists can be modified using built-in functions, as in the examples below.

# Append an element to the end of a list
list_manual = [0, 1, 2, 3, 4]
list_manual.append(5)
print(list_manual)

[0, 1, 2, 3, 4, 5]

# Add an element at a specified position in a list
# insert(position, value) Note that the starting position is 0
list_manual.insert(2, 10)
print(list_manual)

[0, 1, 10, 2, 3, 4, 5]

# Remove an element from the end of a list
list_manual.pop()
print(list_manual)

[0, 1, 10, 2, 3, 4]

# Remove an element at a specified position in a list
# pop(position)
list_manual.pop(2)
print(list_manual)

[0, 1, 2, 3, 4]

• Various other useful functions are also provided by default.

# Count the elements in a list
num_data = len(list_manual)
print(num_data)

5

# Find an element's position (return the first occurrence)
position = list_manual.index(2)
print(position)

2

# Sort a list by value (ascending by default)
list_manual.sort()
print(list_manual)
list_manual.sort(reverse=True)
print(list_manual)

[0, 1, 2, 3, 4]
[4, 3, 2, 1, 0]

# Select a desired segment (slicing)
# Select and return one element
print(list_manual[2])

2

# [A:B] Select positions from A up to, but excluding, B
# [2:4] = select positions 2,3
print(list_manual[2:4])

[2, 1]

# [A:] From position A to the end
# [:B] Select from the start up to, but excluding, B
print(list_manual[2:])
print(list_manual[:4])

[2, 1, 0]
[4, 3, 2, 1]

# [-A] The Ath element from the end
print(list_manual[-2])

1

3.2 Tuples

• A tuple is like a list, but cannot be modified after it is created.
• A tuple starts and ends with ( ); otherwise, its notation is the same as a list.

# Create an empty tuple = effectively pointless, since it cannot be modified.
empty_tuple = ()
print(empty_tuple)

()

# Create by entering values directly
tuple_manual = (0, 1, 2, 3, 4)
print(tuple_manual)

(0, 1, 2, 3, 4)

# Create using range (A, B, C below are all integers)
print(tuple(range(2,10,2)))

(2, 4, 6, 8)

• Except for functions that modify data, the other available functions are almost the same as those for lists.

len(tuple_manual)

5

tuple_manual.index(4)

4

tuple_manual[1:]

(1, 2, 3, 4)

3.3 Sets

• A set is similar to a list, but does not allow duplicate elements.
• A set starts and ends with { }; otherwise, its notation is the same as a list.

# Create an empty set
empty_set = {}
print(empty_set)

{}

# Create by entering values directly - duplicates are removed.
set_manual = {0, 1, 2, 3, 4, 4, 3, 2, 1, 0}
print(set_manual)

{0, 1, 2, 3, 4}

# Create using range (A, B, C below are all integers)
print(set(range(2,10,2)))

{8, 2, 4, 6}

• Since a set is a mathematical set, most mathematical set operations are also available.
• For example,

# Intersection '&'
set_first = {1, 3, 5}
set_second = {1, 2, 4, 8}
print(set_first&set_second)

{1}

# Union '|'
print(set_first|set_second)

{1, 2, 3, 4, 5, 8}

# Difference '-'
print(set_first-set_second)

{3, 5}

# Check whether it is a subset
# A.issuperset(B) - whether B is a subset of A (whether A contains B)
set_third = {1, 3, 5, 7}
set_third.issuperset(set_first)

True

# Check membership
3 in set_first

True

3.4 Dictionaries

• A dictionary is similar to a list, but positions (indices) are managed using arbitrary values called 'keys' instead of integers;

1. Add an item
2. Add an item

is managed.

• Like a set, a dictionary is enclosed in { }, but each entry is stored as a key:value pair.

my_dictionary = {'name':'John', 'age':15, 'height': 1.76}
print(my_dictionary)

{'name': 'John', 'age': 15, 'height': 1.76}

• Selection is also similar to lists, but access uses a 'key' instead of a position (index).

my_dictionary['name']

'John'

• A dictionary can be an element of a list, and vice versa.

first_user = {'name':'John', 'age':15, 'height':1.76, 'position':[15,3]}
second_user = {'name':'Paul', 'age':17, 'height':1.88, 'position':[-2,7]}
users = [first_user, second_user]
print(users[0]['name'])

John