Comprehensions

# Traditional loop
squares = []
for x in range(5):
    squares.append(x * x)

# Pythonic List Comprehension
squares = [x * x for x in range(5)]
print(squares)  # [0, 1, 4, 9, 16]

# With conditionals (only even squares)
even_squares = [x * x for x in range(10) if x % 2 == 0]
print(even_squares)  # [0, 4, 16, 36, 64]

# Map numbers to their square
squares_dict = {x: x * x for x in range(5)}
print(squares_dict)  # {0: 0, 1: 1, 2: 4, 3: 9, 4: 16}

names = ["alice", "bob", "alice", "charlie"]
unique_lengths = {len(name) for name in names}
print(unique_lengths)  # {5, 3, 7}

# Custom iterator that counts up to a limit
class Counter:
    def __init__(self, limit):
        self.limit = limit
        self.current = 0

    def __iter__(self):
        return self

    def __next__(self):
        if self.current < self.limit:
            self.current += 1
            return self.current
        else:
            raise StopIteration

for num in Counter(3):
    print(num)  # Prints: 1, 2, 3

def simple_generator():
    yield "First"
    yield "Second"
    yield "Third"

gen = simple_generator()
print(next(gen))  # "First"
print(next(gen))  # "Second"

# List comprehension (creates list in memory immediately)
list_comp = [x * x for x in range(1000000)]

# Generator expression (computes values lazily on the fly)
gen_exp = (x * x for x in range(1000000))

print(next(gen_exp))  # 0
print(next(gen_exp))  # 1

# File is automatically closed when exiting the block
with open("data.txt", "w") as file:
    file.write("Pythonic Programming")

from contextlib import contextmanager

@contextmanager
def managed_resource():
    print("Acquiring resource... 🔑")
    try:
        yield "Active Resource"  # Passes control to the 'with' block
    finally:
        print("Releasing resource... 🔒")

with managed_resource() as res:
    print(f"Using: {res}")
# Output:
# Acquiring resource... 🔑
# Using: Active Resource
# Releasing resource... 🔒