if / elif / else + ternary

Conditional execution. Truthy values run the if branch; falsy values run else.

script.py v3.1

# Basic if/else
score = 78
if score >= 90:
    grade = 'A'
elif score >= 80:
    grade = 'B'
elif score >= 70:
    grade = 'C'
else:
    grade = 'F'
print(f'score {score} -> grade {grade}')

# Truthy vs falsy
# Falsy: False, None, 0, 0.0, '', [], {}, set()
# Truthy: everything else
values = [0, '', [], None, 1, 'hello', [1], {1: 2}]
for v in values:
    print(f'{v!r:>10} -> {bool(v)}')

# Ternary (one-line if/else)
x = 10
parity = 'even' if x % 2 == 0 else 'odd'
print(f'{x} is {parity}')

# 'in' check
fruits = ['apple', 'banana']
print('apple in fruits:', 'apple' in fruits)
print('cherry in fruits:', 'cherry' in fruits)

Python output click Run to execute

Click "Run" to execute the code on the left.
The output will appear here.

🧠 How it works

if condition: runs the block if condition is truthy. elif = 'else if'. else runs if nothing matched. Python has many falsy values: False, None, 0, 0.0, empty string '', empty list [], empty dict {}, empty set. Everything else is truthy — including non-empty containers, non-zero numbers, and any object. Ternary: value_if_true if condition else value_if_false — read it as 'X if condition else Y'. in checks membership: 'x' in [1, 2, 3], 'k' in dict, 'a' in 'apple'. Avoid '== True' — just use 'if x:' (Pythonic).

✏️ Try these changes

Change score = 78 to score = 95
→ grade becomes A
Change score = 78 to score = 50
→ grade becomes F
Add a value 0.0 to the values list
→ 0.0 is falsy too
Change the ternary to 'odd' if x % 2 else 'even'
→ logic flips — both work

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