# Curly braces
student = {"name": "Alice", "age": 25, "grade": "A"}

# dict() constructor
student = dict(name="Alice", age=25, grade="A")

# From list of tuples
student = dict([("name", "Alice"), ("age", 25), ("grade", "A")])

# From two lists with zip
keys = ["name", "age", "grade"]
values = ["Alice", 25, "A"]
student = dict(zip(keys, values))

# Empty dictionary
empty = {}
empty = dict()

# dict.fromkeys() - all same value
defaults = dict.fromkeys(["a", "b", "c"], 0)
print(defaults)  # {'a': 0, 'b': 0, 'c': 0}

student = {"name": "Alice", "age": 25, "grade": "A"}

# Bracket notation
print(student["name"])   # Alice

# get() method (safer - returns None if key missing)
print(student.get("name"))      # Alice
print(student.get("email"))     # None
print(student.get("email", "N/A"))  # N/A (default value)

# Check if key exists
print("name" in student)     # True
print("email" in student)    # False
print("Alice" in student.values())  # True

student = {"name": "Alice", "age": 25}

# Add or update
student["grade"] = "A"         # Add new key
student["age"] = 26            # Update existing key

# update() - merge another dict
student.update({"city": "NYC", "age": 27})
print(student)
# {'name': 'Alice', 'age': 27, 'grade': 'A', 'city': 'NYC'}

# Merge operator | (Python 3.9+)
defaults = {"theme": "dark", "lang": "en"}
preferences = {"theme": "light", "font": "Arial"}
merged = defaults | preferences
print(merged)  # {'theme': 'light', 'lang': 'en', 'font': 'Arial'}

# |= operator (update in place)
defaults |= preferences
print(defaults)  # {'theme': 'light', 'lang': 'en', 'font': 'Arial'}

# setdefault() - set only if key doesn't exist
student.setdefault("country", "US")
print(student["country"])  # US
student.setdefault("country", "UK")  # Doesn't change
print(student["country"])  # US

student = {"name": "Alice", "age": 25, "grade": "A", "city": "NYC"}

# pop() - remove and return value
age = student.pop("age")
print(age)       # 25
print(student)   # {'name': 'Alice', 'grade': 'A', 'city': 'NYC'}

# pop with default (no error if key missing)
email = student.pop("email", "not found")
print(email)  # not found

# popitem() - remove last inserted pair
last = student.popitem()
print(last)      # ('city', 'NYC')

# del
del student["grade"]
print(student)   # {'name': 'Alice'}

# clear() - remove all
student.clear()
print(student)   # {}

scores = {"Alice": 92, "Bob": 85, "Charlie": 78, "Diana": 95}

# Iterate over keys (default)
for name in scores:
    print(name)

# Iterate over values
for score in scores.values():
    print(score)

# Iterate over key-value pairs
for name, score in scores.items():
    print(f"{name}: {score}")

# Sorted iteration
for name in sorted(scores):
    print(f"{name}: {scores[name]}")

# Sort by value
for name, score in sorted(scores.items(), key=lambda x: x[1], reverse=True):
    print(f"{name}: {score}")
# Diana: 95
# Alice: 92
# Bob: 85
# Charlie: 78

# Basic comprehension
squares = {x: x**2 for x in range(6)}
print(squares)  # {0: 0, 1: 1, 2: 4, 3: 9, 4: 16, 5: 25}

# With condition
even_squares = {x: x**2 for x in range(10) if x % 2 == 0}
print(even_squares)  # {0: 0, 2: 4, 4: 16, 6: 36, 8: 64}

# Transform values
prices = {"apple": 1.20, "banana": 0.50, "cherry": 2.00}
discounted = {item: round(price * 0.9, 2) for item, price in prices.items()}
print(discounted)  # {'apple': 1.08, 'banana': 0.45, 'cherry': 1.8}

# Swap keys and values
original = {"a": 1, "b": 2, "c": 3}
swapped = {v: k for k, v in original.items()}
print(swapped)  # {1: 'a', 2: 'b', 3: 'c'}

# Word frequency
text = "the cat sat on the mat the cat"
word_count = {word: text.split().count(word) for word in set(text.split())}
print(word_count)  # {'the': 3, 'cat': 2, 'sat': 1, 'on': 1, 'mat': 1}

students = {
    "alice": {
        "age": 25,
        "grades": {"math": 92, "science": 88, "english": 95}
    },
    "bob": {
        "age": 22,
        "grades": {"math": 78, "science": 82, "english": 85}
    }
}

# Access nested values
print(students["alice"]["grades"]["math"])  # 92

# Iterate nested
for name, info in students.items():
    avg = sum(info["grades"].values()) / len(info["grades"])
    print(f"{name.title()} — Age: {info['age']}, Average: {avg:.1f}")

text = "hello world hello python world hello"
words = text.split()

# Manual counting
counts = {}
for word in words:
    counts[word] = counts.get(word, 0) + 1
print(counts)  # {'hello': 3, 'world': 2, 'python': 1}

# Using Counter (preferred)
from collections import Counter
counts = Counter(words)
print(counts.most_common(2))  # [('hello', 3), ('world', 2)]

students = [
    ("Alice", "Engineering"),
    ("Bob", "Marketing"),
    ("Charlie", "Engineering"),
    ("Diana", "Marketing"),
    ("Eve", "Science")
]

# Group by department
from collections import defaultdict
departments = defaultdict(list)
for name, dept in students:
    departments[dept].append(name)

for dept, names in departments.items():
    print(f"{dept}: {', '.join(names)}")
# Engineering: Alice, Charlie
# Marketing: Bob, Diana
# Science: Eve

cache = {}

def fibonacci(n):
    if n in cache:
        return cache[n]
    if n <= 1:
        return n
    result = fibonacci(n - 1) + fibonacci(n - 2)
    cache[n] = result
    return result

print(fibonacci(100))  # 354224848179261915075 (instant!)