Lists and Dictionaries in Python

empty_list = []
numbers = [1, 2, 3, 4, 5]
fruits = ["apple", "banana", "orange"]
mixed = ["text", 42, True, 3.14]

fruits = ["apple", "banana", "orange"]
#          0          1          2

print(fruits[0])   # apple
print(fruits[-1])  # orange (last)
print(fruits[-2])  # banana (second to last)

fruits[1] = "pear"   # modify an element
print(len(fruits))   # 3

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

print(numbers[2:5])   # [2, 3, 4]
print(numbers[:5])    # [0, 1, 2, 3, 4]
print(numbers[5:])    # [5, 6, 7, 8, 9]
print(numbers[::2])   # [0, 2, 4, 6, 8]
print(numbers[::-1])  # [9, 8, 7, 6, 5, 4, 3, 2, 1, 0]
print(numbers[-3:])   # [7, 8, 9]

fruits = ["apple", "banana"]

fruits.append("orange")       # add to the end
fruits.insert(1, "pear")      # insert at a position
fruits.remove("banana")       # remove by value (first occurrence)
last = fruits.pop()           # remove and return the last element
first = fruits.pop(0)         # remove and return by index
fruits.clear()                # clear the entire list

numbers = [3, 1, 4, 1, 5, 9, 2]
numbers.sort()                # sort in place → [1, 1, 2, 3, 4, 5, 9]
numbers.sort(reverse=True)    # reverse sort
numbers.reverse()             # reverse in place

print(numbers.count(1))       # 2 — count occurrences
print(numbers.index(4))       # find index of element

list1 = [1, 2, 3]
list1.extend([4, 5, 6])       # add elements from another list

if "banana" in fruits:
    print("We have it!")

if "pear" not in fruits:
    print("No pears")

empty_dict = {}

student = {
    "name": "Anna",
    "age": 16,
    "city": "Moscow",
    "grade": 10
}

# Keys can be strings or numbers
scores = {1: 100, 2: 85, 3: 92}

print(student["name"])  # Anna
print(student["age"])   # 16

student["age"] = 17                  # modify
student["email"] = "a@mail.com"      # add a new key

del student["email"]                 # remove key
age = student.pop("age")             # remove and return value

student = {"name": "Anna", "age": 16, "city": "Moscow"}

# get() — safe lookup (no KeyError)
email = student.get("email", "No email")  # "No email"
age = student.get("age", 0)               # 16

# keys(), values(), items()
print(list(student.keys()))    # ['name', 'age', 'city']
print(list(student.values()))  # ['Anna', 16, 'Moscow']

# update() — update multiple keys at once
student.update({"age": 17, "grade": 11})

# Check key membership
if "name" in student:
    print("Name is present!")

student.clear()  # clear the dictionary

fruits = ["apple", "banana", "orange"]

for fruit in fruits:
    print(fruit)

# With index (enumerate):
for i, fruit in enumerate(fruits, 1):
    print(f"{i}. {fruit}")
# 1. apple
# 2. banana
# 3. orange

student = {"name": "Anna", "age": 16, "city": "Moscow"}

for key in student:              # keys only
    print(key)

for value in student.values():   # values only
    print(value)

for key, value in student.items():  # keys and values
    print(f"{key}: {value}")

tasks = []

# Adding tasks
tasks.append("Study")
tasks.append("Exercise")
tasks.append("Reading")

# Display
print("My tasks:")
for i, task in enumerate(tasks, 1):
    print(f"{i}. {task}")

# Remove a task
tasks.remove("Exercise")
print(f"Remaining: {len(tasks)} tasks")

# Check
if "Study" in tasks:
    print("Study is still pending!")

fruits = ["apple", "banana"]
print(fruits[5])  # ❌ IndexError!
# Check length first: if len(fruits) > 5: ...

student = {"name": "Anna"}
print(student["age"])  # ❌ KeyError!
# Use get(): student.get("age", 0)

# ❌ This is a reference, not a copy:
list2 = list1
list2[0] = 999
print(list1)  # [999, ...] — changed!

# ✅ An actual copy:
list2 = list1.copy()  # or list1[:]