Python validation function pattern

Code pattern

Jump to a topic

See every item in the sequence

Definition

Loop until the input is valid, using try/except for the conversion and if for range checks.

Example

while True: try: n = int(input()) ... except ValueError: ...

Found in: syllabus, course specifications, sample exam and familiarisation guidelines, school notes, past SDD papers.

Where you'll use it in the test

Syllabus area: Code patterns.

Question types it can appear in

Python: Input validation (sample Q18b, fam Q9b)

Where it has appeared in the paper

Secure Software Architecture (Part B, C). Part letters follow each paper’s own layout.

How to use it

A model sentence

General advice, built from the definition and example above

Code pattern: “Loop until the input is valid, using try/except for the conversion and if for range checks.” Then apply it: while True: try: n = int(input()) ... except ValueError: ...

In a short answer, give the definition in your own words first, then tie it to the situation in the question. Do not copy the example above unless it fits the scenario.

Official worked answer

Sample exam Q18b (3 marks): Developing secure code (Python input validation) (3 marks): official criteria and sample answer

Criteria

3: Correct function in Python to check whether a username satisfies the rules. 2: Partially correct function. 1: Some understanding of the problem and Python.

Sample answer

def validate_username(username): valid = True

 # length check
 if len(username) < 8:
      valid = False
 elif (not username[0].isupper()):
      valid = False
 elif (not username[-2].islower()):
      valid = False
 elif (not username[-1].isdigit()):
      valid = False

 return valid

Open the question page

Go deeper

Flashcard: Python validation function pattern in Code Patterns: Pseudocode, Python, SQL, CSS (Years 11 and 12) · study that set
Memorise: Python basics: input, selection, loops, strings
Full term page: every question, note and marking comment for Python validation function pattern

Check yourself

Write or say the “Python validation function pattern” pattern from memory: the syntax and what it does.

Reveal the answer