Learning

Conditional Statements

if Statement

python

age = 20

if age >= 18:
    print('You are an adult')

# One-liner (only for simple cases)
if age >= 18: print('Adult')

if / else

python

age = 15

if age >= 18:
    print('Adult')
else:
    print('Minor')

# One-liner (ternary / conditional expression)
status = 'Adult' if age >= 18 else 'Minor'
print(status)  # 'Minor'

if / elif / else

python

score = 85

if score >= 90:
    grade = 'A'
elif score >= 80:
    grade = 'B'
elif score >= 70:
    grade = 'C'
elif score >= 60:
    grade = 'D'
else:
    grade = 'F'

print(f'Grade: {grade}')  # 'B'

Key points:

Only ONE block executes (first match wins)
elif is short for 'else if'
The else block is optional
Order matters — put most specific conditions first!

Nested Conditions

python

age = 25
has_license = True

if age >= 18:
    if has_license:
        print('Can drive')
    else:
        print('Needs license')
else:
    print('Too young to drive')

# Better: flatten with 'and'
if age >= 18 and has_license:
    print('Can drive')
elif age >= 18:
    print('Needs license')
else:
    print('Too young')

Truthiness in Conditions

python

# These are all VALID conditions
name = 'Alice'
if name:                    # Truthy (non-empty string)
    print(f'Hello {name}')

items = []
if not items:               # Falsy (empty list)
    print('Cart is empty')

value = 0
if value is not None:       # Check for None specifically
    print(f'Value: {value}')

# Dangerous: 0, '', [], None, False all evaluate to False
x = 0
if x:           # This is False!
    print('Won\'t print')

if x is not None:  # This correctly distinguishes 0 from None
    print(f'Value is {x}')  # This prints!

Common Patterns

python

# Early return pattern (guard clauses)
def process(data):
    if data is None:
        return None
    if len(data) == 0:
        return []
    # Main logic here
    return [x * 2 for x in data]

# Match-case (Python 3.10+)
command = 'start'
match command:
    case 'start':
        print('Starting...')
    case 'stop':
        print('Stopping...')
    case 'pause' | 'resume':
        print('Toggling...')
    case _:
        print('Unknown command')

Key Rules

•elif checks are mutually exclusive — only the FIRST matching block runs
•Order matters: put most specific/restrictive conditions BEFORE general ones
•Use 'and' to flatten nested ifs when possible — improves readability
•Use 'is None' / 'is not None' instead of == None or not x (avoids 0/''/[] confusion)
•Ternary expression: value_if_true IF condition ELSE value_if_false — note the order!
•Match-case (Python 3.10+) is cleaner than long if/elif chains for single-value checks

Your Task

Create a function `calculate_bmi(weight_kg, height_m)` that calculates BMI and returns a tuple: (bmi_value, category). Categories: Underweight (<18.5), Normal (18.5-24.9), Overweight (25-29.9), Obese (≥30). Format BMI to 1 decimal place. Also create a function `get_discount(price, customer_type)` where customer_type is 'student', 'senior', 'regular' — student gets 20%, senior 15%, regular 0%. Return discounted price.

Learning

Conditional Statements

if Statement

python

age = 20

if age >= 18:
    print('You are an adult')

# One-liner (only for simple cases)
if age >= 18: print('Adult')

if / else

python

age = 15

if age >= 18:
    print('Adult')
else:
    print('Minor')

# One-liner (ternary / conditional expression)
status = 'Adult' if age >= 18 else 'Minor'
print(status)  # 'Minor'

if / elif / else

python

score = 85

if score >= 90:
    grade = 'A'
elif score >= 80:
    grade = 'B'
elif score >= 70:
    grade = 'C'
elif score >= 60:
    grade = 'D'
else:
    grade = 'F'

print(f'Grade: {grade}')  # 'B'

Key points:

Only ONE block executes (first match wins)
elif is short for 'else if'
The else block is optional
Order matters — put most specific conditions first!

Nested Conditions

python

age = 25
has_license = True

if age >= 18:
    if has_license:
        print('Can drive')
    else:
        print('Needs license')
else:
    print('Too young to drive')

# Better: flatten with 'and'
if age >= 18 and has_license:
    print('Can drive')
elif age >= 18:
    print('Needs license')
else:
    print('Too young')

Truthiness in Conditions

python

# These are all VALID conditions
name = 'Alice'
if name:                    # Truthy (non-empty string)
    print(f'Hello {name}')

items = []
if not items:               # Falsy (empty list)
    print('Cart is empty')

value = 0
if value is not None:       # Check for None specifically
    print(f'Value: {value}')

# Dangerous: 0, '', [], None, False all evaluate to False
x = 0
if x:           # This is False!
    print('Won\'t print')

if x is not None:  # This correctly distinguishes 0 from None
    print(f'Value is {x}')  # This prints!

Common Patterns

python

# Early return pattern (guard clauses)
def process(data):
    if data is None:
        return None
    if len(data) == 0:
        return []
    # Main logic here
    return [x * 2 for x in data]

# Match-case (Python 3.10+)
command = 'start'
match command:
    case 'start':
        print('Starting...')
    case 'stop':
        print('Stopping...')
    case 'pause' | 'resume':
        print('Toggling...')
    case _:
        print('Unknown command')

Key Rules

•elif checks are mutually exclusive — only the FIRST matching block runs
•Order matters: put most specific/restrictive conditions BEFORE general ones
•Use 'and' to flatten nested ifs when possible — improves readability
•Use 'is None' / 'is not None' instead of == None or not x (avoids 0/''/[] confusion)
•Ternary expression: value_if_true IF condition ELSE value_if_false — note the order!
•Match-case (Python 3.10+) is cleaner than long if/elif chains for single-value checks

Your Task