Import statement behavior in Python - Step-by-Step Execution

Concept Flow - Import statement behavior

Start program

↓

Encounter import statement

↓

Check if module is loaded

↓

Use cached

↓

Access module contents

↓

Continue program execution

When Python sees an import, it checks if the module is already loaded. If yes, it uses the cached module. If not, it loads the module, then continues.

Execution Sample

Python

import math
print(math.sqrt(16))
import math
print(math.pi)

This code imports the math module twice and uses its functions and constants.

Execution Table

Step	Action	Module Loaded?	Result	Output
1	import math	No	Load math module
2	print(math.sqrt(16))	Yes	Call sqrt(16)	4.0
3	import math	Yes	Use cached math module
4	print(math.pi)	Yes	Access pi constant	3.141592653589793

💡 Program ends after printing results

Variable Tracker

Variable	Start	After Step 1	After Step 2	After Step 3	After Step 4
math	undefined	module object	module object	module object	module object

Key Moments - 2 Insights

Why does importing the same module twice not reload it?

Because Python checks if the module is already loaded (see Step 3 in execution_table) and uses the cached version to save time.

What happens if you try to use a module before importing it?

You get an error because the module variable is undefined until the import runs (see variable_tracker start state).

Visual Quiz - 3 Questions

Look at the execution table, what is the output after Step 2?

A 4.0

B 16

C Error

D None

💡 Hint

Check the Output column at Step 2 in execution_table

At which step does Python decide to use the cached module instead of loading it again?

A Step 1

B Step 2

C Step 3

D Step 4

💡 Hint

Look at the Module Loaded? and Result columns in execution_table

If the first import was removed, what would happen at Step 2?

A print would output 4.0 anyway

B Error because math is not defined

C math module would be loaded at Step 2

D Program would skip Step 2

💡 Hint

Refer to variable_tracker start state and key moment about using module before import

Concept Snapshot

import module_name

- Loads module if not loaded yet
- Uses cached module if already loaded
- Access module contents with module_name.member
- Importing twice does not reload
- Must import before use

Full Transcript

When Python runs a program and sees an import statement, it checks if the module is already loaded in memory. If not, it loads the module and makes it available. If yes, it uses the cached module to save time. This means importing the same module multiple times does not reload it again. You must import a module before using it, or you get an error. In the example, math is imported first, then used to calculate square root and access pi. The second import just uses the cached math module.