Operators & Expressions

1# ============================================================
2# Arithmetic operators
3# ============================================================
4print(7 / 3)    # 2.3333... (true division — always returns float)
5print(7 // 3)   # 2 (floor division — rounds toward negative infinity)
6print(-7 // 3)  # -3 (NOT -2! Rounds toward negative infinity)
7print(7 % 3)    # 1 (modulus)
8print(-7 % 3)   # 2 (Python's modulus always returns non-negative for positive divisor)
9
10# Exponentiation
11print(2 ** 10)       # 1024
12print(16 ** 0.5)     # 4.0 (square root)
13print(pow(2, 10))    # 1024 (built-in function)
14print(pow(2, 10, 1000))  # 24 (modular exponentiation: 2^10 % 1000)
15
16# ============================================================
17# Comparison chaining (Pythonic!)
18# ============================================================
19age = 25
20
21# BAD (other languages style):
22if age >= 18 and age <= 65:
23    print("Working age")
24
25# GOOD (Pythonic):
26if 18 <= age <= 65:
27    print("Working age")
28
29# Multiple chaining
30x = 5
31print(1 < x < 10)        # True
32print(1 < x < 10 < 100)  # True (all comparisons must be true)
33
34# ============================================================
35# Logical operators: and, or, not
36# ============================================================
37# 'and' returns first falsy value, or last value if all truthy
38print(1 and 2 and 3)    # 3 (all truthy, returns last)
39print(1 and 0 and 3)    # 0 (first falsy value)
40print(1 and "" and 3)   # "" (first falsy value)
41
42# 'or' returns first truthy value, or last value if all falsy
43print(0 or "" or 3)     # 3 (first truthy value)
44print(0 or "" or [])    # [] (all falsy, returns last)
45
46# Practical use: default values
47name = ""
48display_name = name or "Anonymous"  # "Anonymous"
49print(display_name)
50
51# Short-circuit evaluation
52# 'and' stops at first falsy — right side not evaluated
53x = 0
54result = x != 0 and 10 / x  # 10/x never executes (no ZeroDivisionError)
55print(result)  # False
56
57# ============================================================
58# Walrus operator := (Python 3.8+)
59# ============================================================
60# Without walrus — compute twice or use temp variable
61data = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
62
63# BAD: compute len() twice
64# if len(data) > 5:
65#     print(f"List has {len(data)} items")
66
67# GOOD: compute once with walrus
68if (n := len(data)) > 5:
69    print(f"List has {n} items")
70
71# In while loops — read and check in one line
72import io
73buffer = io.StringIO("line1\nline2\nline3\n")
74while (line := buffer.readline()):
75    print(f"Read: {line.strip()}")
76
77# In list comprehensions — filter and transform
78numbers = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
79results = [y for x in numbers if (y := x ** 2) > 20]
80print(results)  # [25, 36, 49, 64, 81, 100]
81
82# ============================================================
83# Membership and identity operators
84# ============================================================
85fruits = ["apple", "banana", "cherry"]
86print("banana" in fruits)       # True
87print("grape" not in fruits)    # True
88
89# 'in' works with strings too
90print("hell" in "hello world")  # True
91
92# 'in' with dictionaries checks keys (not values)
93user = {"name": "Alice", "age": 30}
94print("name" in user)    # True (checks keys)
95print("Alice" in user)   # False (not a key)
96
97# Identity checks
98a = [1, 2, 3]
99b = [1, 2, 3]
100print(a == b)     # True (same value)
101print(a is b)     # False (different objects)
102
103c = a
104print(a is c)     # True (same object)
105
106# ============================================================
107# Bitwise operators
108# ============================================================
109a, b = 0b1010, 0b1100  # 10, 12
110
111print(f"a & b  = {a & b:04b}")   # 1000 (AND)
112print(f"a | b  = {a | b:04b}")   # 1110 (OR)
113print(f"a ^ b  = {a ^ b:04b}")   # 0110 (XOR)
114print(f"~a     = {~a}")           # -11 (NOT — two's complement)
115print(f"a << 2 = {a << 2}")       # 40 (left shift)
116print(f"a >> 1 = {a >> 1}")       # 5 (right shift)
117
118# Practical: using sets with bitwise operators
119set_a = {1, 2, 3, 4}
120set_b = {3, 4, 5, 6}
121print(set_a & set_b)    # {3, 4} — intersection
122print(set_a | set_b)    # {1, 2, 3, 4, 5, 6} — union
123print(set_a ^ set_b)    # {1, 2, 5, 6} — symmetric difference
124print(set_a - set_b)    # {1, 2} — difference