Creating custom modules in Python - Visual Walkthrough

Concept Flow - Creating custom modules

Write functions/classes in a .py file

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Save file as module_name.py

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In another file, use import statement

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Call functions or use classes from module

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Program runs using custom module code

You write code in a file, save it as a module, then import and use it in another file.

Execution Sample

Python

def greet(name):
    return f"Hello, {name}!"

# In another file:
import mymodule
print(mymodule.greet("Alice"))

Defines a greet function in a module and uses it from another file to print a greeting.

Execution Table

Step	Action	Code Line	Result/Output
1	Define function greet in mymodule.py	def greet(name): ...	Function greet created
2	Save file as mymodule.py	File saved	Module ready to import
3	Import mymodule in main.py	import mymodule	Module loaded
4	Call greet with 'Alice'	mymodule.greet("Alice")	Returns 'Hello, Alice!'
5	Print the returned greeting	print(mymodule.greet("Alice"))	Output: Hello, Alice!

💡 Program ends after printing the greeting

Variable Tracker

Variable	Start	After greet('Alice')	Final
name	undefined	"Alice"	undefined after function ends
return value	undefined	"Hello, Alice!"	"Hello, Alice!"

Key Moments - 3 Insights

Why do we save the code in a separate .py file?

Because the module must be a separate file to import it, as shown in execution_table step 2.

What happens when we import the module?

Python loads the module file so we can use its functions, as seen in step 3.

Why do we use the module name before the function call?

To tell Python which module the function comes from, shown in step 4 calling mymodule.greet.

Visual Quiz - 3 Questions

Look at the execution table, what is the output at step 5?

A Hello, Alice!

B greet

C mymodule

D Alice

💡 Hint

Check the 'Result/Output' column in step 5 of the execution_table.

At which step is the module file saved?

A Step 3

B Step 1

C Step 2

D Step 4

💡 Hint

Look for the action mentioning saving the file in the execution_table.

If we forget to import the module, what will happen when calling greet?

A The program prints the greeting anyway

B Python raises an error because greet is undefined

C The program runs but prints nothing

D The module imports automatically

💡 Hint

Think about what happens if you call a function without importing its module, related to step 3 and 4.

Concept Snapshot

Create a Python module by saving functions/classes in a .py file.
Import the module in another file using 'import module_name'.
Call functions with 'module_name.function()'.
This helps organize code and reuse it easily.

Full Transcript

Creating custom modules in Python means writing functions or classes in a separate .py file and saving it. This file becomes a module. In another Python file, you import this module using the import statement. Then you can call the functions or use classes from the module by prefixing them with the module name. For example, if you have a greet function in mymodule.py, you import mymodule and call mymodule.greet('Alice'). The program runs by loading the module and executing the function, printing the greeting. This method helps keep code organized and reusable.