18_zip_enumerate_tutorial.py

# ========== ZIP ==========

# 1. Basic use of zip()
# zip() combines multiple iterable objects into pairs

names = ["Pavel", "Ivan", "Maria"]
ages = [25, 30, 28]

# Combine into pairs (name, age)
pairs = zip(names, ages)
print(f"zip object: {pairs}")  # <zip object>

# Convert to list
pairs_list = list(zip(names, ages))
print(f"Pairs: {pairs_list}")

# 2. Iterating over zip
names = ["Pavel", "Ivan", "Maria"]
ages = [25, 30, 28]

for name, age in zip(names, ages):
    print(f"{name} - {age} years old")

# 3. Three or more lists
names = ["Pavel", "Ivan", "Maria"]
ages = [25, 30, 28]
cities = ["Moscow", "SPb", "Kazan"]

for name, age, city in zip(names, ages, cities):
    print(f"{name}, {age} years old, {city}")

# 4. Different length lists
# zip stops at the shortest list!
names = ["Pavel", "Ivan", "Maria", "Anna"]  # 4 elements
ages = [25, 30]  # 2 elements

pairs = list(zip(names, ages))
print(f"Short zip: {pairs}")  # Only 2 pairs

# 5. zip_longest (itertools) - for lists of different lengths
from itertools import zip_longest

names = ["Pavel", "Ivan", "Maria", "Anna"]
ages = [25, 30]

# fillvalue - value for missing elements
pairs = list(zip_longest(names, ages, fillvalue=None))
print(f"zip_longest: {pairs}")

# 6. Creating dictionary from two lists
keys = ["name", "age", "city"]
values = ["Pavel", 25, "Moscow"]

person = dict(zip(keys, values))
print(f"Dictionary: {person}")

# 7. Unpacking (unzip)
pairs = [("Pavel", 25), ("Ivan", 30), ("Maria", 28)]

# * unpacks list of pairs
names, ages = zip(*pairs)
print(f"Names: {names}")
print(f"Ages: {ages}")

# Note! zip returns tuples, not lists
names_list = list(names)
ages_list = list(ages)
print(f"Names (list): {names_list}")

# 8. Transposing matrix
matrix = [
    [1, 2, 3],
    [4, 5, 6],
    [7, 8, 9]
]

transposed = list(zip(*matrix))
print(f"Transposed: {transposed}")

# Convert tuples back to lists
transposed_lists = [list(row) for row in zip(*matrix)]
print(f"Transposed (lists): {transposed_lists}")

# 9. Parallel iteration with index
names = ["Pavel", "Ivan", "Maria"]
ages = [25, 30, 28]

for i, (name, age) in enumerate(zip(names, ages)):
    print(f"{i}: {name} - {age} years old")

# 10. Combining nested lists
list1 = [1, 2, 3]
list2 = [10, 20, 30]

# Pairwise addition
sums = [a + b for a, b in zip(list1, list2)]
print(f"Sums: {sums}")

# With map
sums_map = list(map(lambda pair: pair[0] + pair[1], zip(list1, list2)))
print(f"Sums (map): {sums_map}")

# ========== ENUMERATE ==========

# 11. Basic use of enumerate()
# enumerate() adds a counter to an iterable object

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

for index, fruit in enumerate(fruits):
    print(f"{index}: {fruit}")

# 12. Starting counter from a different number
fruits = ["apple", "banana", "orange"]

# Start from 1 instead of 0
for index, fruit in enumerate(fruits, start=1):
    print(f"{index}. {fruit}")

# 13. Converting enumerate to list
fruits = ["apple", "banana", "orange"]

indexed = list(enumerate(fruits))
print(f"Indexed list: {indexed}")

indexed_from_1 = list(enumerate(fruits, start=1))
print(f"Indexed from 1: {indexed_from_1}")

# 14. Creating dictionary with indices as keys
fruits = ["apple", "banana", "orange"]

fruit_dict = dict(enumerate(fruits))
print(f"Dictionary: {fruit_dict}")

# 15. Finding element index
fruits = ["apple", "banana", "orange", "banana"]

# Find all indices of "banana"
indices = [i for i, fruit in enumerate(fruits) if fruit == "banana"]
print(f"Indices of 'banana': {indices}")

# 16. Modifying list elements by index
numbers = [10, 20, 30, 40, 50]

# Double every second element
for i, num in enumerate(numbers):
    if i % 2 == 0:
        numbers[i] = num * 2

print(f"Modified list: {numbers}")

# 17. Enumerate with strings
text = "Python"

for index, char in enumerate(text):
    print(f"Position {index}: {char}")

# 18. Enumerate with condition
fruits = ["apple", "banana", "orange", "pear"]

# Print only elements with even indices
for i, fruit in enumerate(fruits):
    if i % 2 == 0:
        print(f"{i}: {fruit}")

# ========== Combining ZIP and ENUMERATE ==========

# 19. zip + enumerate
names = ["Pavel", "Ivan", "Maria"]
ages = [25, 30, 28]

for i, (name, age) in enumerate(zip(names, ages), start=1):
    print(f"{i}. {name} - {age} years old")

# 20. Practical example: comparing two lists
list1 = [1, 2, 3, 4, 5]
list2 = [1, 2, 9, 4, 7]

differences = []
for i, (a, b) in enumerate(zip(list1, list2)):
    if a != b:
        differences.append((i, a, b))

print(f"Differences (index, value1, value2): {differences}")

# 21. Practical example: numbered menu
menu_items = ["New Game", "Load", "Settings", "Exit"]

print("Menu:")
for i, item in enumerate(menu_items, start=1):
    print(f"{i}. {item}")

# 22. Practical example: combining data
first_names = ["Ivan", "Maria", "Peter"]
last_names = ["Ivanov", "Petrova", "Sidorov"]
ages = [25, 30, 28]

people = []
for first, last, age in zip(first_names, last_names, ages):
    people.append({
        "first_name": first,
        "last_name": last,
        "age": age,
        "full_name": f"{first} {last}"
    })

print(f"People: {people}")

# 23. Iterating over pairs of adjacent elements
numbers = [1, 2, 3, 4, 5]

# Pairs (1,2), (2,3), (3,4), (4,5)
pairs = list(zip(numbers, numbers[1:]))
print(f"Adjacent pairs: {pairs}")

# Check for ascending order
is_increasing = all(a < b for a, b in zip(numbers, numbers[1:]))
print(f"List is increasing: {is_increasing}")

# ========== When to use ==========

# ZIP:
# ✅ Parallel iteration over multiple lists
# ✅ Creating dictionaries from keys and values
# ✅ Transposing data
# ✅ Pairwise operations

# ENUMERATE:
# ✅ When you need the index of an element in a loop
# ✅ Creating numbered lists
# ✅ Tracking position in iteration
# ✅ Avoid range(len(list)) - use enumerate!

# Anti-pattern (bad):
fruits = ["apple", "banana"]
for i in range(len(fruits)):
    print(f"{i}: {fruits[i]}")

# Pythonic way (good):
for i, fruit in enumerate(fruits):
    print(f"{i}: {fruit}")