Python programming with sequences of data

DASKEREL wrote this teaching and practice using Oak's sequence as a source. View the source lesson at Oak National Academy. Oak has not endorsed this material. Check Oak's terms and separate rights for third-party works.

Learning outcomes

Store several values in one ordered list
Trace zero-based indices and an out-of-range access

Vocabulary: list · element · index · zero-based · IndexError

Retrieve previous learning

What does assignment do in Python?

Check: It binds a name to a value for later use in the program.

Learn the concept

A Python list holds an ordered sequence of values. In scores = [4, 7, 5], the first item is scores[0] = 4 and the third is scores[2] = 5. Lists allow a program to manage related values without inventing a separate variable for each one. The list can change after creation.

Zero-based indexing makes scores[3] invalid for this three-item list and raises IndexError. len(scores) returns 3, which is a count, not the last valid index. Negative indices count from the end: scores[-1] is 5, though an introductory trace may focus on nonnegative positions.

Write a table of index and value before running code. Use invented numeric examples; do not put names or personal scores into a class exercise. A teacher should observe a learner type, run and correct the program because a written trace alone does not show device competence.

Fictional three-score list

scores = [4, 7, 5]
print(scores[0])
print(len(scores))

The output is 4 then 3 on separate lines.

Run Python in DASKEREL

Use this editor alongside “Create and index a Python list”. Write or change a program, predict its output, then run it. Standard-library Python runs in an isolated browser frame and disposable worker. Each run starts fresh.

Python code

Program input, one answer per lineYour predicted output

Preparing isolated runner…

Output and errors

Run your program to see its output here.

Ready for a longer exercise? Download a DASKEREL notebook for Google Colab. Colab opens separately and does not receive this editor's code automatically.

The Python runtime is downloaded from the pinned Pyodide distribution on first use. Code runs only in this isolated browser frame, with no DASKEREL account access. Programs stop after five seconds; output is capped. This tool does not save code or install packages. Avoid personal or sensitive data.

Worked model

Create scores = [4, 7, 5] and label indices 0, 1, 2.
Trace scores[0] to 4 and len(scores) to 3.
Predict scores[3] raises IndexError before trying it in a supervised environment.
Explain why a count of three does not imply index three exists.

Guided practice

What do colours = ['red', 'blue']; print(colours[1]) display?

Hint: The first element has index zero.

Check the guided answer

It displays blue. Index 1 is the second element in a zero-based list.

Independent practice

Write your own response to every question before viewing the model answers. Your writing stays in this page session; this activity does not submit, store or grade it. Avoid including private information.

Teacher observed practical evidence

A teacher must apply the school's risk assessment, allergy policy and any individual healthcare plan before the practical. Observe and record the criteria during supervised work. Written answers cannot certify practical safety or skill.

Teacher observes an original program running in an approved Python 3 environment using invented data.
Learner traces a test case, identifies and fixes at least one defect, and retains the code and test evidence.
Learner explains the result and limitation without entering private data or running untrusted code.

Find and correct a misconception

“A list with four items has indices 1, 2, 3 and 4.”

Correction: Its nonnegative indices are 0, 1, 2 and 3.

Extend and reflect

Explain what scores[-1] means and compare it with scores[len(scores)-1].

Guidance: Both refer to the final element of a nonempty list; state the nonempty condition.

Where this lesson could lead · Computer Science GCSE → Daskerel Computing and AI

This lesson practises: Store several values in one ordered list. Algorithms, digital systems and safe practice support later software and technology work.

Next school subject: Computer Science GCSE. Check the subject and examination board that fit your school.
Later DASKEREL learning: Daskerel Computing and AI. Explore further study and build evidence from practical work.
Later credential exploration: AWS Certified Developer - Associate is an example in this later specialism. Check current awarding-body requirements before planning an exam.
Example career direction: Software Engineer. Explore organisations and local support.

This is an exploratory route, not a promise of admission, a qualification, certification eligibility or employment. Years 7–9 learning is an early foundation; any later credential may require substantial study, experience or local approval.

Year 9 · Algorithms and programming · original lesson pack

DASKEREL beta · internal AI review pending

Change a list and trace its state

DASKEREL wrote this teaching and practice using Oak's sequence as a source. View the source lesson at Oak National Academy. Oak has not endorsed this material. Check Oak's terms and separate rights for third-party works.

Learning outcomes

Distinguish append, index assignment and removal
Trace list state after several operations

Vocabulary: append · mutation · assignment · remove · state

Retrieve previous learning

What are the indices of a three-element list?

Check: 0, 1 and 2 for nonnegative indexing.

Learn the concept

Lists are mutable. append(value) adds one element at the end; items[1] = value replaces an existing element at index 1; remove(value) removes the first matching value and raises ValueError if absent. These operations have different effects on list length.

Trace one operation per line. Start tasks = ['read', 'draw']; append('test') makes three items; tasks[0] = 'plan' changes the first but keeps length three; remove('draw') leaves ['plan', 'test']. Writing each intermediate state catches the common error of treating assignment as an insertion.

An in-place method such as append changes the list and returns None, so tasks = tasks.append('test') loses the list reference by assigning None. Use the operation as a statement. For real work, consider what happens if a value is missing and test with invented data first.

Original task-list trace

tasks = ['read', 'draw']
tasks.append('test')
tasks[0] = 'plan'
tasks.remove('draw')
print(tasks)

The final display is ['plan', 'test'].

Run Python in DASKEREL

Use this editor alongside “Change a list and trace its state”. Write or change a program, predict its output, then run it. Standard-library Python runs in an isolated browser frame and disposable worker. Each run starts fresh.

Python code

Program input, one answer per lineYour predicted output

Preparing isolated runner…

Output and errors

Run your program to see its output here.

Ready for a longer exercise? Download a DASKEREL notebook for Google Colab. Colab opens separately and does not receive this editor's code automatically.

The Python runtime is downloaded from the pinned Pyodide distribution on first use. Code runs only in this isolated browser frame, with no DASKEREL account access. Programs stop after five seconds; output is capped. This tool does not save code or install packages. Avoid personal or sensitive data.

Worked model

Write the starting list and its two indices.
After append, record ['read', 'draw', 'test'].
After replacement, record ['plan', 'draw', 'test'].
After removal, record ['plan', 'test'] and explain the length change.

Guided practice

What is the final list after x=[2,4]; x.append(6); x[1]=5?

Hint: Append changes length; assignment replaces one existing value.

Check the guided answer

After append it is [2,4,6]; replacing index 1 gives [2,5,6]. Its length remains three after the assignment.

Independent practice

Write your own response to every question before viewing the model answers. Your writing stays in this page session; this activity does not submit, store or grade it. Avoid including private information.

Teacher observed practical evidence

A teacher must apply the school's risk assessment, allergy policy and any individual healthcare plan before the practical. Observe and record the criteria during supervised work. Written answers cannot certify practical safety or skill.

Teacher observes an original program running in an approved Python 3 environment using invented data.
Learner traces a test case, identifies and fixes at least one defect, and retains the code and test evidence.
Learner explains the result and limitation without entering private data or running untrusted code.

Find and correct a misconception

“Setting items[1] adds a new element at index 1.”

Correction: Index assignment replaces an existing element; insertion needs an operation such as insert.

Extend and reflect

Predict remove('x') on a list without 'x'.

Guidance: It raises ValueError; design a presence check before removal if absence is possible.

Where this lesson could lead · Computer Science GCSE → Daskerel Computing and AI

This lesson practises: Distinguish append, index assignment and removal. Algorithms, digital systems and safe practice support later software and technology work.

Next school subject: Computer Science GCSE. Check the subject and examination board that fit your school.
Later DASKEREL learning: Daskerel Computing and AI. Explore further study and build evidence from practical work.
Later credential exploration: AWS Certified Developer - Associate is an example in this later specialism. Check current awarding-body requirements before planning an exam.
Example career direction: Software Engineer. Explore organisations and local support.

This is an exploratory route, not a promise of admission, a qualification, certification eligibility or employment. Years 7–9 learning is an early foundation; any later credential may require substantial study, experience or local approval.

Year 9 · Algorithms and programming · original lesson pack

DASKEREL beta · internal AI review pending

Trace each item in an ordered collection

DASKEREL wrote this teaching and practice using Oak's sequence as a source. View the source lesson at Oak National Academy. Oak has not endorsed this material. Check Oak's terms and separate rights for third-party works.

Learning outcomes

Explain iteration over list elements
Distinguish an element's value from its index

Vocabulary: iteration · element · index · loop body · trace

Retrieve previous learning

How does append differ from index assignment?

Check: Append adds a new final element; index assignment replaces an existing element.

Learn the concept

Iteration repeats a process for each member of a collection. In for score in [3, 5, 2]: print(score), the loop variable score takes the values 3, 5 and 2 in that order. It is a value, not automatically the index 0, 1 or 2.

Indentation marks the loop body in Python. A print inside the body runs three times; a print aligned after the loop runs once when the loop has finished. Trace with columns for iteration number, current value and output. An empty list executes the body zero times.

For a school-approved data activity, use invented values or aggregated non-personal data. A written trace checks understanding but cannot confirm a learner can debug an actual program; observe a run and compare it with the trace.

Iterate three invented scores

for score in [3, 5, 2]:
    print(score)
print('Finished')

Displays 3, 5, 2 and Finished on separate lines.

Run Python in DASKEREL

Use this editor alongside “Trace each item in an ordered collection”. Write or change a program, predict its output, then run it. Standard-library Python runs in an isolated browser frame and disposable worker. Each run starts fresh.

Python code

Program input, one answer per lineYour predicted output

Preparing isolated runner…

Output and errors

Run your program to see its output here.

Ready for a longer exercise? Download a DASKEREL notebook for Google Colab. Colab opens separately and does not receive this editor's code automatically.

The Python runtime is downloaded from the pinned Pyodide distribution on first use. Code runs only in this isolated browser frame, with no DASKEREL account access. Programs stop after five seconds; output is capped. This tool does not save code or install packages. Avoid personal or sensitive data.

Worked model

Write the list order 3, 5, 2.
Trace score taking each value and each indented print.
After the loop, execute the unindented print once.
Repeat the trace with an empty list and explain why only Finished appears.

Guided practice

What prints for for colour in ['red','blue']: print(colour)?

Hint: The variable receives each value, not its index.

Check the guided answer

It prints red then blue on separate lines because the body executes once for each list element.

Independent practice

Write your own response to every question before viewing the model answers. Your writing stays in this page session; this activity does not submit, store or grade it. Avoid including private information.

Teacher observed practical evidence

A teacher must apply the school's risk assessment, allergy policy and any individual healthcare plan before the practical. Observe and record the criteria during supervised work. Written answers cannot certify practical safety or skill.

Teacher observes an original program running in an approved Python 3 environment using invented data.
Learner traces a test case, identifies and fixes at least one defect, and retains the code and test evidence.
Learner explains the result and limitation without entering private data or running untrusted code.

Find and correct a misconception

“A for loop always uses a numeric counter.”

Correction: Python can iterate directly over values in a list; a separate index is only needed for some tasks.

Extend and reflect

Plan a loop that prints item position as well as value.

Guidance: Use enumerate or a separate index and distinguish position from the element itself.

Where this lesson could lead · Computer Science GCSE → Daskerel Computing and AI

This lesson practises: Explain iteration over list elements. Algorithms, digital systems and safe practice support later software and technology work.

Next school subject: Computer Science GCSE. Check the subject and examination board that fit your school.
Later DASKEREL learning: Daskerel Computing and AI. Explore further study and build evidence from practical work.
Later credential exploration: AWS Certified Developer - Associate is an example in this later specialism. Check current awarding-body requirements before planning an exam.
Example career direction: Software Engineer. Explore organisations and local support.

This is an exploratory route, not a promise of admission, a qualification, certification eligibility or employment. Years 7–9 learning is an early foundation; any later credential may require substantial study, experience or local approval.

Year 9 · Algorithms and programming · original lesson pack

DASKEREL beta · internal AI review pending

Use a loop and a condition to process list data

DASKEREL wrote this teaching and practice using Oak's sequence as a source. View the source lesson at Oak National Academy. Oak has not endorsed this material. Check Oak's terms and separate rights for third-party works.

Learning outcomes

Combine iteration with a condition
Trace how an accumulator changes

Vocabulary: accumulator · condition · filter · loop · invariant

Retrieve previous learning

What values does for n in [2,7] assign to n?

Check: It assigns 2, then 7, in list order.

Learn the concept

A loop can select some elements and update a running total. Initialise count = 0 before the loop. For each value, test a condition; if it is true, add one. With values [2, 7, 8], counting even numbers yields 2 because 2 and 8 satisfy value % 2 == 0.

The accumulator must be outside the loop so it retains its value. If count = 0 is indented inside, it resets on every iteration and the final result can be wrong. A trace table records the current value, condition and count after the body for each pass.

A loop over an empty list leaves count at zero. Handle that case explicitly when explaining a result. A classroom test should include no matches, one match and several matches; do not infer correctness from a single successful run.

Count even invented values

count = 0
for value in [2, 7, 8]:
    if value % 2 == 0:
        count += 1
print(count)

The count changes 0 → 1 → 1 → 2, then 2 is printed.

Run Python in DASKEREL

Use this editor alongside “Use a loop and a condition to process list data”. Write or change a program, predict its output, then run it. Standard-library Python runs in an isolated browser frame and disposable worker. Each run starts fresh.

Python code

Program input, one answer per lineYour predicted output

Preparing isolated runner…

Output and errors

Run your program to see its output here.

Ready for a longer exercise? Download a DASKEREL notebook for Google Colab. Colab opens separately and does not receive this editor's code automatically.

The Python runtime is downloaded from the pinned Pyodide distribution on first use. Code runs only in this isolated browser frame, with no DASKEREL account access. Programs stop after five seconds; output is capped. This tool does not save code or install packages. Avoid personal or sensitive data.

Worked model

Set count to zero before entering the loop.
For 2, the remainder is zero and count becomes one; for 7 it stays one.
For 8, the condition is true and count becomes two.
Check the empty-list case prints zero without running the body.

Guided practice

How many values in [1,4,6,9] satisfy value % 2 == 0?

Hint: Test each value and update the count only on true.

Check the guided answer

Two values, 4 and 6, are even. A correctly initialised accumulator ends at 2.

Independent practice

Write your own response to every question before viewing the model answers. Your writing stays in this page session; this activity does not submit, store or grade it. Avoid including private information.

Teacher observed practical evidence

A teacher must apply the school's risk assessment, allergy policy and any individual healthcare plan before the practical. Observe and record the criteria during supervised work. Written answers cannot certify practical safety or skill.

Teacher observes an original program running in an approved Python 3 environment using invented data.
Learner traces a test case, identifies and fixes at least one defect, and retains the code and test evidence.
Learner explains the result and limitation without entering private data or running untrusted code.

Find and correct a misconception

“Putting count = 0 anywhere in the program has the same effect.”

Correction: Its position relative to the loop determines whether the total is preserved or reset.

Extend and reflect

Change the condition to count values greater than 10.

Guidance: Use value > 10, then test boundary values 10 and 11.

Where this lesson could lead · Computer Science GCSE → Daskerel Computing and AI

This lesson practises: Combine iteration with a condition. Algorithms, digital systems and safe practice support later software and technology work.

Next school subject: Computer Science GCSE. Check the subject and examination board that fit your school.
Later DASKEREL learning: Daskerel Computing and AI. Explore further study and build evidence from practical work.
Later credential exploration: AWS Certified Developer - Associate is an example in this later specialism. Check current awarding-body requirements before planning an exam.
Example career direction: Software Engineer. Explore organisations and local support.

This is an exploratory route, not a promise of admission, a qualification, certification eligibility or employment. Years 7–9 learning is an early foundation; any later credential may require substantial study, experience or local approval.

Year 9 · Algorithms and programming · original lesson pack

DASKEREL beta · internal AI review pending

Calculate a total and mean from a list safely

DASKEREL wrote this teaching and practice using Oak's sequence as a source. View the source lesson at Oak National Academy. Oak has not endorsed this material. Check Oak's terms and separate rights for third-party works.

Learning outcomes

Compute a total and arithmetic mean
Handle an empty list before division

Vocabulary: sum · mean · length · division by zero · validation

Retrieve previous learning

Why does an accumulator start before a loop?

Check: It must retain earlier contributions rather than resetting each pass.

Learn the concept

For a list of numeric values, sum(values) calculates their total and len(values) counts them. The arithmetic mean is total divided by count. For [4, 6, 8], the total is 18, the count is 3 and the mean is 6. Units should remain attached to the result.

An empty list has count zero; dividing by len(values) then raises ZeroDivisionError. Check whether the list is nonempty before calculating a mean. Also check that values are numeric and comparable: averaging minutes and seconds without conversion yields a meaningless number.

A mean is a summary, not a complete description. An unusual value can pull it away from typical values; compare a sorted distribution and perhaps a median when appropriate. A program should label the data source, assumptions and whether values were missing.

Mean of invented measurements

values = [4, 6, 8]
if values:
    mean = sum(values) / len(values)
    print(mean)
else:
    print('No values to average')

Displays 6.0 for this list; the empty case avoids division by zero.

Run Python in DASKEREL

Use this editor alongside “Calculate a total and mean from a list safely”. Write or change a program, predict its output, then run it. Standard-library Python runs in an isolated browser frame and disposable worker. Each run starts fresh.

Python code

Program input, one answer per lineYour predicted output

Preparing isolated runner…

Output and errors

Run your program to see its output here.

Ready for a longer exercise? Download a DASKEREL notebook for Google Colab. Colab opens separately and does not receive this editor's code automatically.

The Python runtime is downloaded from the pinned Pyodide distribution on first use. Code runs only in this isolated browser frame, with no DASKEREL account access. Programs stop after five seconds; output is capped. This tool does not save code or install packages. Avoid personal or sensitive data.

Worked model

Calculate 4 + 6 + 8 = 18 and len(values) = 3.
Divide 18 by 3 to predict 6.0 in Python 3.
Follow the if branch for a nonempty list.
Replace values with [] and explain why the else branch runs.

Guided practice

What is the mean of [3, 9]?

Hint: Divide total by count.

Check the guided answer

The total is 12 and count is 2, so the mean is 6.0 in Python 3 division.

Independent practice

Write your own response to every question before viewing the model answers. Your writing stays in this page session; this activity does not submit, store or grade it. Avoid including private information.

Teacher observed practical evidence

A teacher must apply the school's risk assessment, allergy policy and any individual healthcare plan before the practical. Observe and record the criteria during supervised work. Written answers cannot certify practical safety or skill.

Teacher observes an original program running in an approved Python 3 environment using invented data.
Learner traces a test case, identifies and fixes at least one defect, and retains the code and test evidence.
Learner explains the result and limitation without entering private data or running untrusted code.

Find and correct a misconception

“sum([])/len([]) is zero because the sum is zero.”

Correction: The denominator is also zero, so the division is undefined and Python raises ZeroDivisionError.

Extend and reflect

Compare [1,1,10] with [4,4,4].

Guidance: Both have mean 4, but their spreads differ; explain why a decision might need more than the mean.

Where this lesson could lead · Computer Science GCSE → Daskerel Computing and AI

This lesson practises: Compute a total and arithmetic mean. Algorithms, digital systems and safe practice support later software and technology work.

Next school subject: Computer Science GCSE. Check the subject and examination board that fit your school.
Later DASKEREL learning: Daskerel Computing and AI. Explore further study and build evidence from practical work.
Later credential exploration: AWS Certified Developer - Associate is an example in this later specialism. Check current awarding-body requirements before planning an exam.
Example career direction: Software Engineer. Explore organisations and local support.

This is an exploratory route, not a promise of admission, a qualification, certification eligibility or employment. Years 7–9 learning is an early foundation; any later credential may require substantial study, experience or local approval.

Year 9 · Algorithms and programming · original lesson pack

DASKEREL beta · internal AI review pending

Plan, implement and test a small list-based program

DASKEREL wrote this teaching and practice using Oak's sequence as a source. View the source lesson at Oak National Academy. Oak has not endorsed this material. Check Oak's terms and separate rights for third-party works.

Learning outcomes

Break a program brief into data, operations and tests
Explain one defect and its correction with evidence

Vocabulary: specification · test case · edge case · debugging · version

Retrieve previous learning

What special case needs a check before calculating the mean of a list?

Check: An empty list, because its length is zero.

Learn the concept

A small project should solve a bounded task. A fictional club score analyser can store invented points in a list, display the count and highest value, and report 'No results' for an empty list. Write acceptance criteria and expected outputs before coding. Avoid collecting real classmates' scores or names.

Implement a simple version first, then add one feature at a time. max(values) works only when values is nonempty. A conditional such as if values: chooses the safe branch. Keep the code readable with names that state their purpose and comments only where a choice is not obvious.

Test ordinary, boundary and empty cases against expected results. If a test fails, record the input, expected output, observed output and code change. A successful run on one example does not establish correctness. A teacher should inspect the saved program and watch the learner explain and debug it.

Fictional club result summary

points = [3, 5, 4]
if points:
    print('Count:', len(points))
    print('Highest:', max(points))
else:
    print('No results')

For this invented list, outputs Count: 3 and Highest: 5 on separate lines.

Run Python in DASKEREL

Use this editor alongside “Plan, implement and test a small list-based program”. Write or change a program, predict its output, then run it. Standard-library Python runs in an isolated browser frame and disposable worker. Each run starts fresh.

Python code

Program input, one answer per lineYour predicted output

Preparing isolated runner…

Output and errors

Run your program to see its output here.

Ready for a longer exercise? Download a DASKEREL notebook for Google Colab. Colab opens separately and does not receive this editor's code automatically.

The Python runtime is downloaded from the pinned Pyodide distribution on first use. Code runs only in this isolated browser frame, with no DASKEREL account access. Programs stop after five seconds; output is capped. This tool does not save code or install packages. Avoid personal or sensitive data.

Worked model

Write criteria for a count, highest value and empty-list message.
Build the list and conditional, then predict the output for [3,5,4].
Test [0], [] and [3,5,4], comparing observed with expected output.
Record one defect, correction and retest; save the version for teacher review.

Guided practice

What happens if max(points) runs when points=[]?

Hint: max needs an item to choose from.

Check the guided answer

It raises ValueError because there is no maximum in an empty list. Put max inside an if points: branch and give a defined empty-case message.

Independent practice

Write your own response to every question before viewing the model answers. Your writing stays in this page session; this activity does not submit, store or grade it. Avoid including private information.

Teacher observed practical evidence

A teacher must apply the school's risk assessment, allergy policy and any individual healthcare plan before the practical. Observe and record the criteria during supervised work. Written answers cannot certify practical safety or skill.

Teacher observes an original program running in an approved Python 3 environment using invented data.
Learner traces a test case, identifies and fixes at least one defect, and retains the code and test evidence.
Learner explains the result and limitation without entering private data or running untrusted code.

Find and correct a misconception

“One successful program run proves every possible input works.”

Correction: Different ordinary, boundary and empty cases can reveal different defects; testing gives evidence within its tested scope.

Extend and reflect

Add a mean feature while keeping the empty case safe.

Guidance: Use sum(points)/len(points) only inside the nonempty branch and label the resulting number.