np.save() and np.load() for binary in NumPy - Step-by-Step Execution

Concept Flow - np.save() and np.load() for binary

Create numpy array

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Call np.save(filename, array)

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Array saved as binary file

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Call np.load(filename)

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Binary file read into numpy array

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Use loaded array in program

First, you save a numpy array to a binary file using np.save(). Later, you load it back with np.load() to get the same array.

Execution Sample

NumPy

import numpy as np
arr = np.array([1, 2, 3])
np.save('data.npy', arr)
loaded_arr = np.load('data.npy')
print(loaded_arr)

This code saves a numpy array to a file and then loads it back, printing the loaded array.

Execution Table

Step	Action	Input/Condition	Result/Output
1	Create array	arr = [1, 2, 3]	arr is numpy array [1 2 3]
2	Save array	np.save('data.npy', arr)	File 'data.npy' created with binary data
3	Load array	loaded_arr = np.load('data.npy')	loaded_arr is numpy array [1 2 3]
4	Print loaded array	print(loaded_arr)	Output: [1 2 3]
5	End	No more code	Execution stops

💡 All steps completed, array saved and loaded successfully

Variable Tracker

Variable	Start	After Step 1	After Step 3	Final
arr	undefined	[1 2 3]	[1 2 3]	[1 2 3]
loaded_arr	undefined	undefined	[1 2 3]	[1 2 3]

Key Moments - 3 Insights

Why does np.save() create a file instead of returning data?

np.save() writes the array directly to a binary file on disk, so it does not return data but creates a file you can load later (see step 2 in execution_table).

What type is the object returned by np.load()?

np.load() returns a numpy array loaded from the binary file, exactly like the original array (see step 3 and 4 in execution_table).

Can you use np.load() without saving first?

No, np.load() needs a file created by np.save() or similar. If the file doesn't exist, it will cause an error.

Visual Quiz - 3 Questions

Look at the execution_table, what is the value of 'loaded_arr' after step 3?

A undefined

B [1 2 3]

C [3 2 1]

D None

💡 Hint

Check the 'Result/Output' column for step 3 in execution_table.

At which step is the binary file 'data.npy' created?

A Step 1

B Step 3

C Step 2

D Step 4

💡 Hint

Look for the action 'Save array' in execution_table.

If you change the array before saving to [4,5,6], what will be printed at step 4?

A [4 5 6]

B Error

C [1 2 3]

D Empty array

💡 Hint

The saved file stores the array at save time, so loading will return the saved array (see variable_tracker).

Concept Snapshot

np.save(filename, array) saves a numpy array to a binary file.
np.load(filename) loads the array back from the file.
The saved file has .npy extension by convention.
Use these to store and retrieve arrays efficiently.
np.save does not return data, it writes to disk.
np.load returns the original numpy array.

Full Transcript

This visual execution shows how np.save() writes a numpy array to a binary file and np.load() reads it back. First, an array is created. Then np.save() writes it to 'data.npy'. Next, np.load() reads the file and returns the array. Finally, printing shows the loaded array matches the original. Variables 'arr' and 'loaded_arr' track the array before and after saving/loading. Key points include understanding that np.save creates a file and np.load returns a numpy array. The quiz checks understanding of variable values and file creation steps.