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+---- Thread: CHAPTER 10 — Conditions & If Statements (/showthread.php?tid=228)
CHAPTER 10 — Conditions & If Statements - Leejohnston - 11-15-2025
Chapter 10 — Conditions & If Statements
This is where your programs start thinking for themselves.
Up until now, your programs ran the same way every time.
Conditions let your code choose between different actions, based on:
• user input
• numbers
• comparisons
• logic
---
10.1 Comparison Operators
Python uses the following:
Code:
== equal to
!= not equal to
> greater than
< less than
>= greater or equal
<= less or equalExamples:
Code:
print(5 > 2) # True
print(3 == 4) # False
print("a" != "b") # True---
10.2 Basic if Statement
Code:
age = 16
if age >= 18:
print("You can enter.")If the condition is False, Python skips the inside block.
---
10.3 if–else
Code:
age = 16
if age >= 18:
print("Adult ticket")
else:
print("Child ticket")---
10.4 if–elif–else (Multiple Options)
Code:
temp = 30
if temp > 35:
print("Too hot!")
elif temp > 20:
print("Warm")
else:
print("Cold")---
10.5 Logical Operators
Combine conditions:
Code:
and # both must be true
or # at least one is true
not # reverses a conditionExamples:
Code:
age = 25
has_id = True
if age >= 18 and has_id:
print("Entry approved")---
10.6 Nested Conditions
Code:
age = 20
member = True
if age >= 18:
if member:
print("VIP Entry")
else:
print("Standard Entry")---
10.7 Comparing Strings
Code:
name = "lee"
if name.lower() == "lee":
print("Welcome, Lee!")String comparisons must match exactly unless you force lowercase.
---
10.8 Typical Beginner Mistakes
❌ Using = instead of ==
Code:
if age = 18: # WRONG✔ Correct:
Code:
if age == 18:❌ Forgetting indentation
Python uses 4 spaces (or a tab).
---
10.9 Mini Project — Grade Checker
Ask the user for a score from 0–100.
Output:
• A if ≥ 90
• B if ≥ 80
• C if ≥ 70
• D if ≥ 60
• Fail otherwise
---
10.10 Challenge — Login System
Ask the user:
• username
• password
Stored credentials:
• username = admin
• password = python123
Correct → “Login successful”
Wrong → “Access denied”
BONUS:
• allow 3 attempts
---
10.11 Chapter Summary
• if statements execute only when True
• else handles all other cases
• elif checks additional conditions
• comparison operators compare values
• and, or, not combine logic
• indentation matters
• strings should be normalised (lowercase)
Next:
Chapter 11 — Loops & Repetition
Where you learn how to make Python repeat actions efficiently without writing the same line 50 times.
---
Written and Compiled by Lee Johnston — Founder of The Lumin Archive