u03-slides-data-structures-flashcards
What are the main types of data structures in Python?
Sequence types (list, tuple, string, range), unordered collections (set), and mapping types (dictionary)
How is a list created in Python?
Using square brackets containing comma-separated values (e.g.
What is special about Python lists?
They are mutable, can contain mixed data types, can be nested, and preserve order
At what index do Python sequences start?
0
What is the difference between lists and tuples?
Tuples are immutable (cannot be changed after creation), while lists are mutable
How are tuples created in Python?
Using comma-separated values, optionally enclosed in parentheses (e.g., my_tuple = 42, “text”, 3.14)
What is a set in Python?
An unordered collection of unique elements, created using set() or curly braces
Set:
A collection of unordered, mutable, and unique elements.
Defined using curly braces {} or the set() constructor.
Example:
my_set = {1, 2, 3}
my_set = set([1, 2, 3]) # Alternative
What are common set operations in Python?
Union (|), intersection (&), difference (-)
What is a dictionary in Python?
A mutable and ordered collection of key-value pairs
How are dictionaries created in Python?
Output: {‘key1’: ‘value1’, ‘key2’: ‘value2’, ‘key3’: ‘value3’}
1. Using Curly Braces
my_dict = {
"key1": "value1",
"key2": "value2",
"key3": "value3"
}
print(my_dict)
2. Using the dict() Constructor
my_dict = dict(key1="value1", key2="value2", key3="value3")
print(my_dict)
# Output: {'key1': 'value1', 'key2': 'value2', 'key3': 'value3'}
3. From a List of Tuples
- Convert a list of key-value tuples into a dictionary:
my_dict = dict([("key1", "value1"), ("key2", "value2"), ("key3", "value3")])
print(my_dict)
# Output: {'key1': 'value1', 'key2': 'value2', 'key3': 'value3'}
4. Using Dictionary Comprehension
- Create a dictionary dynamically:
my_dict = {x: x**2 for x in range(1, 4)}
print(my_dict)
# Output: {1: 1, 2: 4, 3: 9}
5. From Two Separate Iterables
- Use the zip() function to pair keys and values:
keys = ["key1", "key2", "key3"]
values = ["value1", "value2", "value3"]
my_dict = dict(zip(keys, values))
print(my_dict)
# Output: {'key1': 'value1', 'key2': 'value2', 'key3': 'value3'}
6. Empty Dictionary
- Create an empty dictionary:
my_dict = {}
print(my_dict)
# Output: {}
What can be used as dictionary keys?
Any hashable object
What can be used as dictionary values?
Any object
What is a list comprehension?
Explain the key concepts!
Output: [0, 1, 4, 9, 16]
A compact way to create a list by looping over an iterable, with optional filtering and transformations
Key Concepts:
- Basic Syntax:
[expression for item in iterable]
- With Filter:
[expression for item in iterable if condition]
- Transform and Filter Together:
[transform for item in iterable if condition]
Create a list of squares using list comprehension (base values zero to five)
Simple List Comprehension
A list comprehension creates a new list by iterating over an existing sequence.
Example 1: Create a list of squares
squares = [x**2 for x in range(5)] print(squares)
Filter even numbers using list comprehension for the integer numbers from zero to ten
Output: [0, 2, 4, 6, 8]
List Comprehension with Filters
You can add a condition to include only certain elements in the resulting list.
Example 2: Filter even numbers
even_numbers = [x for x in range(10) if x % 2 == 0] print(even_numbers)
Using list comprehension create a list containing the double value of each element in a range from 0 to 5.
Output: [0, 2, 4, 6, 8]
List Comprehension with Transformers
You can apply a transformation to each element in the list.
Example 3: Double the value of each element
doubled_numbers = [x * 2 for x in range(5)] print(doubled_numbers)
Create a list of the squares of the odd numbers from 0 to 10 using list comprehension.
Output: [1, 9, 25, 49, 81]
Combining Filters and Transformers
You can filter elements and then transform them in the same comprehension.
Example 4: Squares of odd numbers
odd_squares = [x**2 for x in range(10) if x % 2 != 0] print(odd_squares)
What does this output
Example 5: Create a multiplication table
multiplication_table = [[i * j for j in range(1, 4)] for i in range(1, 4)] print(multiplication_table)
Output: [[1, 2, 3], [2, 4, 6], [3, 6, 9]]
[[1, 2, 3], [2, 4, 6], [3, 6, 9]]
You can use a list comprehension inside a
Nested List Comprehension
What is the syntax for slicing in Python?
sequence[start:end:step] where start is inclusive and end is exclusive
What happens when using negative numbers in slicing?
They count from the end (-1 for last element, -2 for second-last, etc.)
What is unpacking in Python?
Tuple unpacking
Assigning values from a sequence directly to multiple variables (e.g., a, b, c = [1, 2, 3])
How to unpack the following tuple or list into x, y coordinates?
point = (3, 4)
Unpacking a Tuple or List
point = (3, 4) x, y = point print(x) # Output: 3 print(y) # Output: 4 List unpacking colors = ["red", "green", "blue"] a, b, c = colors print(a, b, c) # Output: red green blue
What will the following code do and what do you call the operation?
numbers = [1, 2, 3, 4, 5] a, b, *rest = numbers start, *middle, end = numbers
Using * for Variable-Length Unpacking
numbers = [1, 2, 3, 4, 5] First two into separate variables, the rest into another a, b, *rest = numbers print(a, b, rest) # Output: 1 2 [3, 4, 5] Collect the middle values start, *middle, end = numbers print(start, middle, end) # Output: 1 [2, 3, 4] 5
What does this code do and what du you call the operaton?
pairs = [(1, 'a'), (2, 'b'), (3, 'c')]
for number, letter in pairs:
print(f"Number: {number}, Letter: {letter}")
Unpacking in a Loop
pairs = [(1, 'a'), (2, 'b'), (3, 'c')]
for number, letter in pairs:
print(f"Number: {number}, Letter: {letter}")
# Output:
# Number: 1, Letter: a
# Number: 2, Letter: b
# Number: 3, Letter: c
