Data Types & Structures Loops & Control Flows

# ── int ──────────────────────────────────────────────────────x = 42big  = 1_000_000      # underscores improve readabilitybin_ = 0b1010         # binary literal  → 10hex_ = 0xFF           # hex literal     → 255print(x, big, bin_, hex_) # ── float ─────────────────────────────────────────────────────pi  = 3.14159sci = 2.5e3           # scientific notation → 2500.0print(pi, sci) # ── complex ───────────────────────────────────────────────────c = 3 + 4jprint(c.real, c.imag) # 3.0  4.0print(abs(c))         # 5.0  (magnitude √(3²+4²)) # ── type conversion ───────────────────────────────────────────print(int(3.9))       # 3   ← truncates, does NOT roundprint(float(7))       # 7.0print(str(42))        # '42'print(bool(0))        # Falseprint(bool(-5))       # True # ── useful built-ins ──────────────────────────────────────────print(abs(-15))            # 15print(round(3.14159, 2))   # 3.14print(pow(2, 10))          # 1024print(divmod(17, 5))       # (3, 2)  quotient and remainderprint(max(3, 7, 1, 9))     # 9print(min(3, 7, 1, 9))     # 1

s = "  Hello, Python World!  " # ── case & whitespace ─────────────────────────────────────────print(s.strip())          # "Hello, Python World!"print(s.lower())print(s.upper())print("hElLo".swapcase()) # "HeLlO" # ── search ────────────────────────────────────────────────────t = "Hello, Python World!"print(t.find("Python"))       # 7  (index; -1 if not found)print(t.count("l"))           # 3print(t.startswith("Hello"))  # Trueprint(t.endswith("!"))        # True # ── test ──────────────────────────────────────────────────────print("123".isdigit())    # Trueprint("abc".isalpha())    # Trueprint("abc123".isalnum()) # True # ── modify ────────────────────────────────────────────────────print(t.replace("Python", "Data Science"))print("a,b,c,d".split(","))           # ['a', 'b', 'c', 'd']print("-".join(["2024", "01", "15"]))  # '2024-01-15' # ── f-strings ─────────────────────────────────────────────────name  = "Alice"score = 98.567print(f"{name} scored {score:.2f}%")   # Alice scored 98.57%print(f"{'Python':^20}")               # centred in 20 charsprint(f"{42:08b}")                     # 00101010 (binary)

text = "Python"nums = [10, 20, 30, 40, 50] # ── indexing ──────────────────────────────────────────────────print(text[0], text[-1])    # P  nprint(nums[2], nums[-2])    # 30  40 # ── slicing strings ───────────────────────────────────────────print(text[0:3])   # Pytprint(text[2:])    # thonprint(text[:3])    # Pytprint(text[::2])   # Pto   every 2nd charprint(text[::-1])  # nohtyP  reversed # ── slicing lists ─────────────────────────────────────────────print(nums[1:4])   # [20, 30, 40]print(nums[::2])   # [10, 30, 50]print(nums[::-1])  # [50, 40, 30, 20, 10] # ── slicing returns a NEW object ──────────────────────────────subset = nums[1:3]print(subset)      # [20, 30]print(nums)        # [10, 20, 30, 40, 50]  unchanged

fruits = ["apple", "banana", "cherry"] # ── add ───────────────────────────────────────────────────────fruits.append("date")                 # add to endfruits.insert(1, "avocado")           # insert at index 1fruits.extend(["elderberry", "fig"])  # add multipleprint(fruits) # ── remove ────────────────────────────────────────────────────fruits.remove("avocado")   # remove by value (first match)popped = fruits.pop()      # remove & return last itemprint(f"Popped: {popped}") # ── search ────────────────────────────────────────────────────nums = [3, 1, 4, 1, 5, 9, 2, 6]print(nums.index(4))    # 2print(nums.count(1))    # 2 # ── sort ──────────────────────────────────────────────────────nums.sort()             # in placeprint(nums)words = ["banana", "apple", "cherry"]print(sorted(words))    # new list  — original unchangedprint(words) # ── mutability: two names, same list ─────────────────────────a = [1, 2, 3]b = ab.append(4)print(a)        # [1, 2, 3, 4]  ← also changed!c = a.copy()    # independent copyc.append(99)print(a)        # [1, 2, 3, 4]  ← unchanged

# ── creating tuples ───────────────────────────────────────────point  = (3, 7)rgb    = (255, 128, 0)single = (42,)       # trailing comma required! # ── access ────────────────────────────────────────────────────print(point[0])     # 3print(rgb[-1])      # 0print(rgb[0:2])     # (255, 128) # ── unpacking ─────────────────────────────────────────────────x, y = pointprint(f"x={x}, y={y}") r, g, b = rgbprint(f"R={r} G={g} B={b}") first, *rest = (1, 2, 3, 4, 5)print(first, rest)   # 1  [2, 3, 4, 5] # ── immutable ─────────────────────────────────────────────────try:    point[0] = 10except TypeError as e:    print(f"TypeError: {e}") # ── tuple as dict key ─────────────────────────────────────────loc = {(28.6, 77.2): "Delhi", (19.1, 72.9): "Mumbai"}print(loc[(28.6, 77.2)])   # Delhi # ── count & index ─────────────────────────────────────────────t = (1, 2, 2, 3, 2)print(t.count(2), t.index(3))   # 3  3

person = {"name": "Alice", "age": 28, "city": "Jaipur"} # ── access ────────────────────────────────────────────────────print(person["name"])             # Aliceprint(person.get("salary"))      # None  (no KeyError)print(person.get("salary", 0))   # 0     (default) # ── add / update ──────────────────────────────────────────────person["email"] = "alice@example.com"person["age"]   = 29person.update({"city": "Delhi", "role": "analyst"})print(person) # ── remove ────────────────────────────────────────────────────removed = person.pop("email")print(f"Removed: {removed}") # ── iterate ───────────────────────────────────────────────────for key, value in person.items():    print(f"  {key}: {value}") # ── membership check ──────────────────────────────────────────print("name"   in person)   # Trueprint("salary" in person)   # False # ── setdefault ────────────────────────────────────────────────person.setdefault("country", "India")print(person["country"])    # India

# ── range variants ────────────────────────────────────────────for i in range(5):          print(i, end=" ")   # 0 1 2 3 4print()for i in range(1, 6):       print(i, end=" ")   # 1 2 3 4 5print()for i in range(0, 20, 5):   print(i, end=" ")   # 0 5 10 15print()for i in range(10, 0, -2):  print(i, end=" ")   # 10 8 6 4 2print() # ── iterating a list and string ───────────────────────────────fruits = ["apple", "banana", "cherry"]for fruit in fruits:    print(fruit.upper()) for char in "Python":    print(char, end="-")   # P-y-t-h-o-n-print() # ── enumerate: index + value ──────────────────────────────────for i, fruit in enumerate(fruits, start=1):    print(f"{i}. {fruit}") # ── zip: pair two lists ───────────────────────────────────────names  = ["Alice", "Bob", "Charlie"]scores = [92, 85, 78]for name, score in zip(names, scores):    print(f"{name}: {score}") # ── iterating a dictionary ────────────────────────────────────grades = {"Maths": "A", "Science": "B", "English": "A"}for subject, grade in grades.items():    print(f"{subject} → {grade}")

# ── basic while ───────────────────────────────────────────────count = 1while count <= 5:    print(f"Count: {count}")    count += 1print("Done!") # ── countdown ─────────────────────────────────────────────────n = 10while n > 0:    print(n, end=" ")    n -= 3print(f"\nFinal n: {n}") # ── while-else ────────────────────────────────────────────────attempts = 0while attempts < 3:    attempts += 1    print(f"Attempt {attempts}")else:    print("All attempts used")   # runs when loop ends naturally # ── search (break skips the else) ─────────────────────────────items  = [4, 7, 2, 9, 1, 5]target = 9i = 0while i < len(items):    if items[i] == target:        print(f"Found {target} at index {i}")        break    i += 1else:    print(f"{target} not found")   # skipped because break fired

# ── break ─────────────────────────────────────────────────────print("-- break --")for i in range(1, 10):    if i == 5:        print("Reached 5, stopping!")        break    print(i)              # prints 1 2 3 4 # ── continue ──────────────────────────────────────────────────print("-- continue --")for i in range(1, 8):    if i % 2 == 0:        continue          # skip even numbers    print(i)              # prints 1 3 5 7 # ── pass ──────────────────────────────────────────────────────print("-- pass --")for i in range(5):    if i == 2:        pass              # placeholder — handle later    else:        print(i)          # prints 0 1 3 4 # ── break + else pattern ──────────────────────────────────────numbers = [3, 7, 12, 5, 8]for num in numbers:    if num > 10:        print(f"First > 10: {num}")        breakelse:    print("None greater than 10")   # runs only if no break

# ── basic ─────────────────────────────────────────────────────squares = [x**2 for x in range(1, 6)]print(squares)     # [1, 4, 9, 16, 25] # ── with condition ────────────────────────────────────────────evens = [x for x in range(20) if x % 2 == 0]print(evens)       # [0, 2, 4, 6, 8, 10, 12, 14, 16, 18] # ── transform strings ─────────────────────────────────────────words = ["hello", "world", "python"]upper = [w.upper() for w in words]print(upper)       # ['HELLO', 'WORLD', 'PYTHON'] # ── filter AND transform ──────────────────────────────────────fruits = ["apple", "Banana", "cherry", "Date", "elderberry"]long_lower = [f.lower() for f in fruits if len(f) > 5]print(long_lower)  # ['banana', 'cherry', 'elderberry'] # ── equivalent for-loop (more verbose) ────────────────────────result = []for f in fruits:    if len(f) > 5:        result.append(f.lower())print(result)      # same result # ── nested: flatten a 2D list ─────────────────────────────────matrix = [[1, 2, 3], [4, 5, 6], [7, 8, 9]]flat   = [num for row in matrix for num in row]print(flat)        # [1, 2, 3, 4, 5, 6, 7, 8, 9]

# ── immutable int: reassignment creates a NEW object ─────────x = 10y = xx = 20print(y)        # 10  — y unaffected # ── immutable str: methods return a new string ───────────────s = "hello"t = ss = s.upper()   # s → "HELLO" (new object)print(t)        # "hello"  — t unchanged # ── mutable list: shared reference ────────────────────────────a = [1, 2, 3]b = a           # b is NOT a copy!b.append(4)print(a)        # [1, 2, 3, 4]  ← a also changed # ── fix with .copy() ──────────────────────────────────────────c = a.copy()c.append(99)print(a)        # [1, 2, 3, 4]  ← unchangedprint(c)        # [1, 2, 3, 4, 99] # ── mutable dict: same shared-reference behaviour ────────────d1 = {"x": 1}d2 = d1d2["y"] = 2print(d1)       # {'x': 1, 'y': 2}  ← shared! # ── immutable tuple ───────────────────────────────────────────try:    (1, 2, 3)[0] = 99except TypeError as e:    print(f"TypeError: {e}") print("Mutable  :", ["list", "dict", "set"])print("Immutable:", ["int", "float", "str", "tuple", "bool"])