Module 4 Quick Reference: Conditionals

Comparison Operators

Operator	Meaning	Example	Result
`==`	Equal to	`5 == 5`	`True`
`!=`	Not equal to	`5 != 3`	`True`
`<`	Less than	`3 < 5`	`True`
`>`	Greater than	`5 > 3`	`True`
`<=`	Less than or equal	`5 <= 5`	`True`
`>=`	Greater than or equal	`7 >= 10`	`False`

Remember: = is assignment, == is comparison!

if / elif / else Syntax

# Basic if
if condition:
    # code runs if condition is True

# if-else
if condition:
    # runs if True
else:
    # runs if False

# if-elif-else
if condition1:
    # runs if condition1 is True
elif condition2:
    # runs if condition2 is True
elif condition3:
    # runs if condition3 is True
else:
    # runs if none above are True

Key rules: Colon : after every if/elif/else. Indent the block with 4 spaces. Only the first True branch runs in an elif chain.

Logical Operators

Operator	Meaning	Example	Result
`and`	Both must be True	`True and False`	`False`
`or`	At least one True	`True or False`	`True`
`not`	Reverses the value	`not True`	`False`

Precedence: not → and → or (use parentheses to be clear)

Common Patterns

# Range check
if 1 <= x <= 100:   # Python supports chained comparisons!

# Case-insensitive comparison
if name.lower() == "alice":

# Checking for valid input
if user_input.isdigit():

# Guard clause (check failures first)
if not logged_in:
    print("Please log in")
elif not has_permission:
    print("Access denied")
else:
    # do the actual work

Common Mistakes

Mistake	Fix
`if x = 5:` (assignment)	`if x == 5:` (comparison)
Forgetting the colon `:`	Always end if/elif/else with `:`
Wrong indentation	Use exactly 4 spaces per level
`"5" == 5` (type mismatch)	`int("5") == 5`
`"Yes" == "yes"` (case)	`"Yes".lower() == "yes"`

Short-Circuit Evaluation

# and: stops at first False
if x != 0 and 10/x > 2:   # Safe: won't divide if x is 0

# or: stops at first True
if is_admin or is_owner:     # Skips is_owner check if is_admin is True