Conditionals (if/elif/else)

Objective

Write conditional logic in Python using if/elif/else, boolean operators, and ternary expressions.

Tools & Technologies

if
elif
else
bool
and/or/not
ternary

Key Commands

if x > 0:

elif x < 0:

else:

result = 'yes' if condition else 'no'

x and y or z

Architecture Overview

flowchart TD COND{condition is True?} -->|True| IF_BODY[if block executes] COND -->|False| ELIF{elif condition?} ELIF -->|True| ELIF_BODY[elif block] ELIF -->|False| ELSE[else block] IF_BODY --> CONT[Continue] ELIF_BODY --> CONT ELSE --> CONT style COND fill:#1a1a2e,stroke:#00d4ff,color:#e0e0e0

Step-by-Step Process

Basic if/elif/else

Standard conditional structure.

x = 10
if x > 0:
    print('positive')
elif x < 0:
    print('negative')
else:
    print('zero')

# Compound conditions
if age >= 18 and country == 'CA':
    print('eligible')

# in operator
if name in ['Alice', 'Bob', 'Charlie']:
    print('known user')

Truthy and Falsy Values

Python coerces values to bool in conditions.

# Falsy: False, None, 0, 0.0, '', [], {}, set()
# Truthy: everything else

if name:           # True if name is non-empty
    print(name)

if data:           # True if list is non-empty
    process(data)

# Pattern: if not value to check for empty
if not errors:
    print('All OK')

Ternary Expression

One-line conditional assignment.

# Traditional
if score >= 60:
    grade = 'pass'
else:
    grade = 'fail'

# Ternary
grade = 'pass' if score >= 60 else 'fail'

# Nested ternary (use sparingly)
label = 'high' if x > 100 else ('mid' if x > 50 else 'low')

Challenges & Solutions

= is assignment, == is comparison — classic bug in conditions
chained comparisons work in Python: 0 < x < 100 is valid

Key Takeaways

Python has no switch statement (until 3.10 match) — use elif chains or dicts
Short-circuit evaluation: in 'a and b', if a is False, b is never evaluated