Harshit Saini
Harshit Saini's Blog

Harshit Saini's Blog

Modules in Python

Modules in Python

Harshit Saini
·Apr 3, 2021·

3 min read

Subscribe to my newsletter and never miss my upcoming articles

Creating Modules

As our program grows we should split our code across multiple files. We refer to each file as a module. A module should contain related data, functions, and objects.

def calc_tax():
    pass

def calc_shipping():
    pass

Importing a module

Now we can import those functions to this file.

# import
from sales import calc_tax

# use it
calc_tax()

# ==============================

# import multiple functions 
from sales import calc_tax, calc_shipping

# ==============================

# import everything 
from sales import *

another way of importing

# import
import sales 

# use
sales.calc_tax()

Even if we imported only one function then also the entire module needs to be loaded.


Compiled Python Files

When we will compile the app.py file using the command python app.py then python will create a folder names __pycache__

In this folder, there will be a compiled version of the module that you just imported in the app.py file.

This is done to speed up compilation. And this will speed up the loading of the module.

This will not speed up the performance of the program.

app.py is not cached because the entry file is always recompiled.


Module Search Path

If the python compiler does not find the module in the current folder then it will search for the file in a bunch of predefined folders.

The built in modules like sys are kept in these folders.


Package

Packages are used if the file that we want to use is inside a sub folder.

The folder structure looks like this.

Untitled.png

We can not do this -

# we can not do this 
from ./ecommerce/sales import tax

We have to create a __init__.py file in the ecommerce folder. When we create this file then python will think of this folder as a package.

A package is a folder that contains one or more modules.

So a module is a file and a package is a folder.

The __init__.py file is empty.

Untitled 1.png

Now you can import and use it in three ways

# way 1
import ecommerce.sales

ecommerce.sales.tax()

# =========================
# way 2 
from ecommerce.sales import tax, sales

tax()

# =========================
# way 3
import sales from ecommerce

sales.tax()

Sub-packages

Now we have to create another __init__.py file in the sub folder also

Our folder structure is like this

Untitled 2.png now import like this

from ecommerce.shopping import sales

Intra Package Reference

This simply means, using one package into another package.

Untitled 3.png

In our sales modules, we want to use the contact module.

we can use absolute import

from ecommerce.customer import contact
contact.customer()

we can use relative import

from ../customer import contact
contact.customer()

The dir Function

This function will give us all the functions that are defined in a module

from ecommerce.shopping import sales 

print(dir(sales))

some functions such as__name__ , __package__ , etc are already defined for us.

print(__name__)
print(__package__)
print(__file__)

'''
These functions give us the file name of the module,
the package name and the address of the module 
'''

The name of the module that starts our program is always __main__

Did you find this article valuable?

Support Harshit Saini by becoming a sponsor. Any amount is appreciated!

Learn more about Hashnode Sponsors
 
Share this