NUMPY / FOUNDATIONS

Array creation, indexing, axes, and shapes

Learn how array creation, indexing, axes, and shapes works in NumPy, why the underlying model matters, and how to apply it in a small program without hiding important trade-offs.

What you will learn

Explain array creation in NumPy using the correct mental model
Trace a focused NumPy example and predict its result before execution
Recognize a boundary case involving indexing and handle it deliberately

Understanding Array creation, indexing, axes, and shapes

Array creation, indexing, axes, and shapes belongs to the practical core of NumPy. Start by identifying the values or state involved and the rule that connects the input to the result.

Trace the example one operation at a time. Keep array creation visible in the code rather than hiding it behind an abstraction before the behavior is understood.

Test a normal case and a boundary case. The difference between the prediction and the observed result is the most useful signal for deciding what to review next.

Key idea

Array creation, indexing, axes, and shapes is a defining part of practical NumPy work. Start by identifying the data or state involved, then trace the operation that changes or interprets it. Pay attention to the rules NumPy applies at this boundary, because those rules explain both the useful behavior and the common failure modes. This lesson keeps the example deliberately small, then connects it to names, views, copies, and memory sharing so the ideas form a coherent progression rather than a list of isolated syntax facts.

Worked examples

EXAMPLE 1

Array creation, indexing, axes, and shapes example

Open workspace

A focused NumPy example for array creation.

import numpy as np
values = np.array([1, 2, 3])
print(values.sum())

# Lesson 2: array creation. Change one value and predict the result before running it.

Example explained

Line 1Identify where array creation appears in the NumPy example and name the data it operates on.

Line 2Trace the relevant NumPy rule one operation at a time, recording any state, type, or control-flow change.

Line 3Change one input or boundary condition, predict the result, and compare that prediction with the documented outcome.

Important notes

Remember

Keep the first array creation example small enough to trace completely.

Good practice

Use the normal NumPy toolchain or browser workspace to compare the actual result with your prediction.

Common mistakes

Watch this boundary

Treating array creation as punctuation to memorize instead of a NumPy behavior to reason about.

Watch this boundary

Ignoring indexing until it appears in production data or a larger program.

Try it yourself

PRACTICE TASK

Change, predict, then run

Create a small NumPy example that demonstrates array creation. Add a normal case and a boundary case, write down the expected result for each, then explain which NumPy rule produces that result. Lesson 2 should remain small enough to trace without guessing.

Open NumPy workspace

Check your understanding

What is the best first step when working with array creation?

Identify the data and predict the result
Add more abstraction immediately
Ignore boundary cases
Memorize punctuation only

Show answer

A clear input, operation, and predicted result create a testable mental model.