Bioinformatics Laboratory at BiUH.
Core Values: Respect, Reflection, Communication, Commitment.
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Section 5. Data Structures in Action
Section 1. Lists
1.1. What is a List?
Like a shopping list that can hold multiple items
# Shopping list example
groceries = ["apples", "milk", "eggs", "bread"]
print("My shopping list:" + str(groceries))
1.2. Four Ways to Create Lists
- Square brackets
[]
colors = ["red", "green", "blue"]
list()constructor
numbers = list((1, 2, 3)) # Converts tuple to list
1.3. More Creation Methods
- List comprehension
squares = [x**2 for x in range(5)]
# [0, 1, 4, 9, 16]
- Convert from string
word = list("hello")
# ['h', 'e', 'l', 'l', 'o']
1.4. Accessing Elements
Positive indexing:
games = ["Mario", "Zelda", "Pokémon"]
print(games[0]) # Mario
print(games[-1]) # Pokémon (negative index)
1.5. Slicing Lists
Get sub-lists with [start:end]
months = ["Jan", "Feb", "Mar", "Apr", "May"]
print(months[1:3]) # ['Feb', 'Mar']
print(months[:2]) # First two: ['Jan', 'Feb']
print(months[3:]) # Last two: ['Apr', 'May']
1.6. Adding Items
append() and insert()
todo = ["wake up"]
todo.append("brush teeth") # Add to end
todo.insert(1, "make bed") # Insert at position 1
print(todo) # ['wake up', 'make bed', 'brush teeth']
Q: todo.insert(0,’start’) ? todo.insert(len(todo),’end1’) ? todo.insert(-1,’end2’) ?
1.7. Removing Items
remove() and pop()
pets = ["cat", "dog", "hamster"]
pets.remove("dog") # Remove by value
last = pets.pop() # Remove last item
print(pets) # ['cat']
print(last) # 'hamster'
Q: pets=[“dog”, “bird”, “dog”, ‘cat’,”dog”]; pets.remove(“dog”) ?
Q: pets.index(‘dog’)?
1.8. Sorting Lists
sort() method
scores = [88, 92, 75, 100]
scores.sort()
print(scores) # [75, 88, 92, 100]
# Reverse sort
scores.sort(reverse=True)
print(scores) # [100, 92, 88, 75]
1.9. Practice: Student Grades System
Store multiple students’ scores
students = ["Alice", "Bob", "Charlie"]
scores = [88, 92, 75]
1.10. Calculate Average
total = sum(scores)
average = total / len(scores)
print("Class average: " + str(average))
# Output: Class average: 85.0
Q: how to convert the “+” to a f-string format (f””)?
1.11. Sort Scores
Combine data with zip()
combined = []
i=0
while i<len(scores):
combined.append( [scores[i], students[i]] )
i=i+1
combined.sort()
print("Ranking:")
for one in combined:
print(str(one[1]) + ": " + str(one[0]))
Q: sort in reverse order?
Section 2. Tuples
2.1. Tuples vs Lists: Immutability Demo
# Lists are mutable
fruits = ["apple", "banana", "cherry"]
fruits[0] = "avocado"
print(fruits) # Changes successfully
# Tuples are immutable (unchangeable)
colors = ("red", "green", "blue")
colors[0] = "pink"
# report error
Key difference: 📌 Tuples use () while lists use [] 📌 Tuple elements cannot be changed after creation
2.2. Why Immutability Matters?
Real-life examples of unchangeable data:
- Geographic coordinates (latitude, longitude)
- RGB color codes
- Date components (year, month, day)
# Valid tuple usage
black = (0, 0, 0)
current_position = (37.7749, -122.4194)
2.3. Tuple Unpacking
Basic unpacking:
dimensions = (1920, 1080)
width, height = dimensions
print("Screen: " + str(width) + "x" + str(height))
Swapping variables:
a = 5
b = 10
a, b = b, a
2.4. Advanced Unpacking Tricks
Ignoring values:
coordinates = (45, -73, 100)
lat, lon, _ = coordinates
Multiple assignment:
# Get first and last items
numbers = (3, 1, 4, 1, 5, 9)
first, *middle, last = numbers
Q: what is the content of “middle” ?
2.5. Single-element Tuple Trap
Common mistake:
not_a_tuple = (42)
print(type(not_a_tuple)) # <class 'int'>
Correct way:
proper_tuple = (42,)
print(type(proper_tuple)) # <class 'tuple'>
Visual reminder: ❗ Always add comma for single items ❗
Q: proper_tuple[0] ? proper_tuple[1] ?
2.6. Returning Multiple Values
Simple example:
def circle_calc(radius):
area = 3.14 * radius ** 2
circumference = 2 * 3.14 * radius
return (area, circumference)
results = circle_calc(5)
print("Area: " + str(results[0]) + ", Circumference: " + str(results[1]))
Better usage with unpacking:
area, circ = circle_calc(7)
print("Area is " + str(area) + " units")
2.7. When to Use Tuples?
Perfect for:
- Data that shouldn’t change (constants)
- Dictionary keys (unlike lists!)
- Function return values
- Protecting important data
# Valid dictionary key
locations = {
(40.7128, -74.0060): "New York",
(51.5074, -0.1278): "London"
}
2.8. Tuple Operations Summary
Essential methods:
my_tuple = (1, 2, 3)
print(len(my_tuple)) # 3
print(2 in my_tuple) # True
print(my_tuple.index(2)) # 1
print(my_tuple.count(2)) # 1
Remember:
No append/remove/pop methods!
Section 3. Dictionaries
3.1. Phone Book Analogy 📞
# Think of dictionaries like phone contacts:
phone_book = {
"Alice": "555-1234",
"Bob": "555-5678",
"Charlie": "555-9012"
}
print(phone_book["Alice"]) # Outputs: 555-1234
3.2. Three Ways to Create Dictionaries
Method 1: Curly Braces {}
student = {"name": "Emma", "age": 20, "major": "CS"}
Method 2: dict() Constructor
colors = dict(red="#FF0000", green="#00FF00")
Method 3: List of Tuples
weekdays = dict([(1, "Mon"), (2, "Tue"), (3, "Wed")])
3.3. Adding & Changing Entries
animal_sounds = {}
animal_sounds["dog"] = "Woof!" # Add new entry
animal_sounds["cat"] = "Mew" # Add another
animal_sounds["cat"] = "Meow" # Update existing
print(animal_sounds) # {'dog': 'Woof!', 'cat': 'Meow'}
3.4. Removing Entries
del animal_sounds["dog"] # Delete entry
removed = animal_sounds.pop("cat")
print(removed) # "Meow"
print(animal_sounds) # Empty now
3.5. Safe Value Access with get()
grades = {"Math": 90, "Science": 85}
print(grades.get("History", "Subject not found"))
# Outputs: Subject not found
3.6. Building a Simple Translator
nano translator.py
translator = {
"hello": "hola",
"goodbye": "adiós",
"thank you": "gracias"
}
word = input("Enter English word: ").lower()
translation = translator.get(word, "Translation not available")
print("Spanish: " + str(translation))
3.7. Handling Unknown Words
if translation == "Translation not available":
print("Please check spelling!")
print("Current dictionary words:" + str(list(translator.keys())))
3.8. Dictionary Methods Summary
my_dict = {"a": 1, "b": 2}
print(my_dict.keys()) # dict_keys(['a', 'b'])
print(my_dict.values()) # dict_values([1, 2])
print(my_dict.items()) # dict_items([('a', 1), ('b', 2)])
3.9. Real-World Example: Movie Ratings
nano movie_rating.py
movies = {
"Moana": 7.5,
"Toy Story": 8.6,
"Frozen": 8.5
}
movie = input("Enter movie title: ")
print("Rating: " + str(movies.get(movie, "Not in database")) + "/10")
3.10. Dictionary Power Tips 💡
- Keys can be numbers/strings/tuples
- Values can be ANY data type
- Fast lookup speed
- Great for organizing related data
mixed_example = {
1: "Number key",
(2,3): "Tuple key",
"list": ["can", "be", "value"]
}
Section 4. Sets
4.1. What Makes Sets Special?
- Unique Elements: Automatically removes duplicates
- Unordered: No index-based access
- Mutable: Can add/remove elements
- Math Operations: Built-in set operations
4.2. Automatic Deduplication Demo
# List vs Set comparison
fruits_list = ['apple', 'banana', 'apple', 'orange']
fruits_set = {'apple', 'banana', 'apple', 'orange'}
print("List: " + str(fruits_list)) # Keeps duplicates
print("Set: " + str(fruits_set)) # Auto-removes duplicates
4.3. Real-World Deduplication Example
# Removing duplicate votes
votes = ['Alice', 'Bob', 'Alice', 'Charlie', 'Bob']
unique_voters = set(votes)
print("Total votes: " + str(len(votes)))
print("Unique voters: " + str(len(unique_voters)))
4.4. Set Operations: Intersection
# Common elements in both sets
art_students = {'Tom', 'Alice', 'Bob', 'Eve'}
music_students = {'Alice', 'Eve', 'John'}
both = art_students & music_students
print("Students in both clubs: " + str(both))
4.5. Set Operations: Union
# Combine sets (no duplicates)
week1_customers = {'Alice', 'Bob'}
week2_customers = {'Bob', 'Charlie'}
all_customers = week1_customers | week2_customers
print("All customers: " + str(all_customers))
4.6. Set Operations: Difference
# Elements in first set not in second
available_colors = {'red', 'blue', 'green'}
used_colors = {'blue', 'yellow'}
remaining = available_colors - used_colors
print("Remaining colors: " + str(remaining))
4.7. Voting System Case Study
nano vote.py
# Counting unique votes
votes = []
while True:
vote = input("Enter candidate name (or 'done'): ")
if vote.lower() == 'done':
break
votes.append(vote)
unique_votes = set(votes)
print("Candidates: " + ', '.join(unique_votes))
Q: how can we get the number of votes? hint: use dict
4.8. Friend Finder System
# Finding common friends
alice_friends = {'Bob', 'Charlie', 'Diana'}
bob_friends = {'Charlie', 'Diana', 'Eve'}
common = alice_friends & bob_friends
print("Common friends: " + str(common))
# Adding new friend
alice_friends.add('Eve')
print("Updated friends: " + str(alice_friends))
4.9. Set Methods Cheat Sheet
| Method | Example | Description |
|---|---|---|
add() |
s.add('x') |
Add element |
remove() |
s.remove('x') |
Remove element |
clear() |
s.clear() |
Empty the set |
copy() |
new_set = s.copy() |
Create duplicate |
List also has “clear()” and “copy()”
4.10. Why Use Sets?
- Fast membership testing:
'a' in set - Mathematical operations: Easy intersections/unions
- Data cleaning: Quick duplicate removal
- Relationship modeling: Social networks, groups
Q: write a program to get all unique letters in your name?
Section 5. Data Structures in Action
5.1. Student Information System Demo
0. A demo
a = []
def add():
a.append(1)
add()
print(a)
a = set()
def add():
a.add(1)
add()
print(a)
a = {}
def add():
a[1]=1
add()
print(a)
a=0
def add():
print(a)
add()
print(a)
a=0
def add():
a=a+1
add()
print(a)
Q: What happended here ?
mutable variable: list, dict, set
Variable “assignment” and “modifying its contents” (mutable) are two different things!
Assignment = replacing the box → requires global
Modifying contents = changing what’s inside the box → no global needed
5.2. Storing Students
# Create empty list
students = []
# Create student dictionary
student1 = {
"name": "Alice",
"age": 20,
"major": "Computer Science"
}
students.append(student1)
5.3. Adding Students
def add_student():
name = input("Enter name: ")
age = int(input("Enter age: "))
major = input("Enter major: ")
new_student = {
"name": name,
"age": age,
"major": major
}
students.append(new_student)
print("Student added!")
5.4. Sorting Students
Q: add two students, order students by age ?
5.5. Word Frequency Analyzer
1. Splitting Text
text = "apple banana orange apple pear orange apple ok yes yes ok no no want"
words = text.lower().split()
print(words)
5.6. Counting Words
word_counts = {}
for word in words:
if word in word_counts:
word_counts[word] += 1
else:
word_counts[word] = 1
print(word_counts)
5.7. Finding TOP5 Words
Q: How can we get top5 words?
End