What is wrong branch order?

A broad condition placed first captures values meant for a later branch; order from highest or most specific.

What is bad indentation?

Python uses indentation to group a branch's statements; inconsistent spaces cause errors or wrong behaviour.

SingaporeComputer ScienceSyllabus dot point

How does Python make decisions with if, elif and else, and how do we build conditions?

Use Python selection with if, elif and else, build conditions with comparison and logical operators, and order branches correctly

A focused answer to the O-Level Computing point on Python selection. Using if, elif and else, comparison operators, combining conditions with and, or and not, and ordering branches so each value falls into the right one.

Generated by Claude Opus 4.87 min answerUpdated 2026-06-06

Reviewed by: AI editorial process; not yet individually human-reviewed

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What this dot point is asking
The answer
Examples in context
Try this

What this dot point is asking

SEAB wants you to use selection in Python with if, elif and else, to build conditions with comparison and logical operators, and to order branches so every value goes into the intended one. The central idea is that selection lets a program choose what to do based on a condition, and the order and combination of conditions decide which branch runs.

The answer

if, elif and else

Selection chooses between blocks of code:

if temperature > 30:
    print("Hot")
elif temperature > 20:
    print("Warm")
else:
    print("Cool")

Python tests the conditions top to bottom. The first true condition runs its block, and the rest are skipped. elif (else if) adds more cases; else catches everything not matched above. Indentation (four spaces) shows which lines belong to each branch.

Comparison operators

A condition usually compares two values:

Operator	Meaning
`==`	equal to
`!=`	not equal to
`>`	greater than
`<`	less than
`>=`	greater than or equal to
`<=`	less than or equal to

Note == tests equality; a single = assigns a value, which is a common slip.

Combining conditions

Logical operators join or reverse conditions:

and: true only if both sides are true.
or: true if either side is true.
not: reverses a condition.

if age >= 13 and age <= 19:
    print("Teenager")

Ordering branches

When ranges meet, order matters. Check the most specific or highest band first, so a value is caught by the right branch:

if mark >= 75:      # checked first
    grade = "A"
elif mark >= 60:    # only reached if below 75
    grade = "B"

If you checked >= 60 first, a mark of $80$ would wrongly be labelled "B".

Worked example

Write a program that reads a year and prints whether it is a "Child" (under $13$ ), "Teenager" ( $13$ to $19$ ) or "Adult" ( $20$ and over) by age.

Step 1: Read and convert the input

age = int(input("Enter age: "))

Step 2: Check the lowest band first

if age < 13:
    print("Child")

Step 3: Add the middle band with elif

Because the Child case has been handled, this branch is only reached for ages $13$ and over:

elif age <= 19:
    print("Teenager")

Step 4: Catch the rest with else

else:
    print("Adult")

The branches cover every age exactly once: under $13$ , then up to $19$ , then everything else.

Examples in context

Example 1. A ticket price calculator. A cinema program uses if/elif/else on age to set a child, standard or senior price. Checking the bands in order, youngest first, ensures each customer gets exactly one correct price with no overlap.

Example 2. Validating a menu choice. A program checks if choice == 1 ... elif choice == 2 ... else: print("Invalid"). The final else handles any unexpected input, so a wrong key gives a clear message rather than silently doing nothing.

Try this

Q1. State the difference between = and == in Python. [2 marks]

Cue. = assigns a value to a variable; == tests whether two values are equal.

Q2. Write a condition that is true when score is at least $50$ and at most $100$ . [2 marks]

Cue. if score >= 50 and score <= 100:.

Q3. Explain why the order of if and elif branches matters with overlapping ranges. [2 marks]

Cue. The first true branch runs, so a broad condition placed too early captures values meant for a later, more specific branch.

Exam-style practice questions

Practice questions written in the style of SEAB exam questions on this dot point, with worked answer explainers. The year tag is the paper they imitate, not the source.

Original6 marksWrite a Python program that reads a mark out of

100

and prints a grade: 'A' for

75

and above, 'B' for

60

74

, 'C' for

50

59

, and 'Fail' below

50

Show worked answer →

Use an if/elif/else chain, checking the highest band first:

mark = int(input("Enter mark: "))
if mark >= 75:
    print("A")
elif mark >= 60:
    print("B")
elif mark >= 50:
    print("C")
else:
    print("Fail")

Because the branches are checked top to bottom, once mark >= 75 is false we know the mark is below $75$ before testing >= 60, so each range is covered exactly once.

Markers reward converting the input to an int, the correct boundaries ( $\ge 75$ , $\ge 60$ , $\ge 50$ , else), and ordering the conditions from highest to lowest.

Original5 marks(a) Write a condition that is true only when a number `n` is between

1

and

10

inclusive. (b) Write a condition that is true when a character `c` is 'y' or 'Y'. (c) State what the operator `not` does in a condition.

Show worked answer →

(a) Combine two comparisons with and:

if n >= 1 and n <= 10:

Both parts must be true, so n must be at least $1$ and at most $10$ .

(b) Combine two equality tests with or:

if c == "y" or c == "Y":

Either match makes the condition true.

Markers reward and for the inclusive range, or for the two characters, and not reversing a condition's truth value.