items = ["apple", "banana", "cherry"]
items.append("date")          # add to end
items.insert(1, "avocado")     # insert at index
items.pop()                    # remove last
print(items[0])               # "apple" — 0-indexed
print(items[-1])              # last element
print(items[1:3])             # slice [1,3) = ["avocado","banana"]

# List comprehension — Pythonic and fast
squares = [x**2 for x in range(10) if x % 2 == 0]
# [0, 4, 16, 36, 64]

user = {"name": "Ajay", "age": 28, "city": "Mumbai"}
user["email"] = "ajay@example.com"   # add key
user.get("phone", "N/A")            # safe get with default

# Dict comprehension
word_len = {w: len(w) for w in ["python", "java", "c++"]}
# {"python": 6, "java": 4, "c++": 3}

# Iterating
for key, val in user.items():
    print(f"{key}: {val}")

coords = (19.07, 72.87)          # lat, lon of Mumbai
lat, lon = coords                  # tuple unpacking

# Use tuples for fixed data that should not change
# e.g. HTTP status codes, RGB colours, database records
HTTP_OK = (200, "OK")

tags = {"python", "ml", "llm", "python"}  # duplicates removed
print(tags)  # {"python", "ml", "llm"}

# Set operations — fast membership testing O(1)
a = {1,2,3,4}
b = {3,4,5,6}
print(a & b)   # {3, 4}  — intersection
print(a | b)   # {1,2,3,4,5,6} — union
print(a - b)   # {1, 2}  — difference

# List comprehension — replaces most for loops
even_squares = [x**2 for x in range(20) if x % 2 == 0]

# Dict comprehension — used constantly with API responses
response_data = [{"id": 1, "name": "alice"}, {"id": 2, "name": "bob"}]
id_map = {item["id"]: item["name"] for item in response_data}
# {1: "alice", 2: "bob"}

# Generator — lazy evaluation, memory efficient for large data
def token_chunks(text: str, size: int):
    words = text.split()
    for i in range(0, len(words), size):
        yield " ".join(words[i:i+size])

# Use with large LLM context windows
for chunk in token_chunks(long_document, 500):
    process(chunk)   # never loads full doc into memory

# zip and enumerate — essential for pairing data
names  = ["alice", "bob", "charlie"]
scores = [85, 92, 78]
for i, (name, score) in enumerate(zip(names, scores)):
    print(f"{i}: {name} = {score}")