Create a Python Email Validator

Objective: Building a Email Validator in Python where script can processing a list of user inputs to generate a report of valid email addresses and their domains.

It demonstrates:

variables,
control structures (nested loops and conditionals),
functions,
exception handling,
functions (including *args and **kwargs)
basic string manipulation
pytest (for testing script)

What new Concept covered

`*args` (Variable Positional Arguments):

What: Allows a function to accept any number of positional arguments (e.g., generate_report(emails, "personal", "work")).
Why: Flexible for functions that need varying inputs (e.g., categories).
Where: Used in scripts or APIs to handle dynamic inputs.
New: *categories collects extra arguments as a tuple.
Exceptions: Misusing *args with incorrect types (handled by checking category.lower()).

`**kwargs` (Variable Keyword Arguments):

What: Allows a function to accept any number of keyword arguments similar like key-value pair (e.g., show_invalid=True).
Why: Provides optional configuration without fixed parameters.
Where: Common in utilities or APIs for customizable behavior.
New: **options collects keyword arguments as a dictionary; accessed with .get().
Exceptions: Missing keys (handled with .get(default)).

String Manipulation:

What: Uses split('@'), in operator, and lower() for email validation and domain extraction.
Why: Processes text data efficiently.
Where: Parsing user inputs or logs.
New: Basic email validation checks for @and a domain.
Exceptions: Invalid emails cause IndexError (handled in is_valid_email).

Nested Loops and `any()`:

What: Nested loop in list comprehension (any(category.lower() in email.lower() ...)).
Why: Checks if any category matches an email, simplifying control flow.
Where: Filtering data based on multiple criteria.
New: any() is a Python built-in that returns True if any element in an iterable is True.
Exceptions: Empty iterables or case mismatches (handled with lower()).

Pytest:

What: A testing framework for Python to write and run tests.
Why: Automates verification of code functionality, ensuring reliability.
Where: Used in development to validate logic and in CI/CD pipelines for DevOps.
New: Tests are written as functions with assert statements; pytest discovers and runs them.
Exceptions: Test failures indicate bugs or incomplete test coverage.

Test Functions:

What: Functions like test_is_valid_email() that check specific behaviors.
Why: Isolates functionality for targeted validation.
Where: Unit testing individual components (e.g., email validation).
New: Prefix with test_ for pytest to recognize; use descriptive assertions.
Exceptions: Overly specific tests may break with minor code changes.

Importing Modules:

What: Importing functions from email_validator.py (e.g., from basics.email_validator import ...).
Why: Tests need access to the code being tested.
Where: Common in modular projects with separate test files.
New: Path-based import requires correct directory structure.
Exceptions: Incorrect paths cause ModuleNotFoundError.

Project summary

Processing a list of user inputs to generate a report of valid email addresses and their domains.
Understand difference and use of *args and **kwargs in functions.
Why pytest needed - Automates verification of code functionality, ensuring reliability. .
Importing Modules - Tests need access to the code being tested

Structure

core-python
├── basics
│   └── email_validator
│       ├── README.md
│       └── main.py
└── tests
    └── test_email_validator.py

email_validator/main.py email validator script.
test_email_validator.py test script for email validator.

How I Built it

Build a pseudo flow chart with pen and paper.
Start writing code:
- Let’s start with main():
  - Execute each step with considering pseudo flow chart.
  - emails assign to a list of emails.
  - report1 assign to generate_report(emails) which return only valid emails.
  - report2 assign to generate_report(emails, "personal") which return only emails which has personal in it.
  - report3 assign to generate_report(emails, show_invalid=True) which return all emails (including invalid).
  - print_report() do the printing work.

About generate_report():
- Generate report depending on passed arguments.
- Take three arguments:
  - emails take all provided emails
  - *categories take all remaining argument after emails.
  - **options take only key-pair type argument. (e.g. show_invalid=True)
- Return:
  - → dict[str, list[str]] means a dictionary which has domain name and it’s corresponding email in a list.

About is_valid_email():
- Check weather email is valid or not.
- Has email parameter which takes email.
- Return: → bool means return be True or False.

About extract_domain():
- Extract the domain from a valid email.
- Has email parameter which takes email.
- Return: → str means return be
  - if email valid domain.com
  - if email is invalid ” “.

About print_report():
- First check report empty or not then do the printing work on report.
- Has report parameter which take a report.
- Return: → None means no return.

How to run

Change directoru to core-python, so that test can also be performed.

 # optional: in python-foundation dir
 # source venv/bin/activate    # Windows: venv\Scripts\activate
 cd core-python

Run main.py.

 python3 basics/email_validator/main.py

Output:

 Report 1: All valid emails

     Domain: gmail.com
       - alice@gmail.com

     Domain: work.com
       - bob@work.com

     Domain: yahoo.com
       - charlie.personal@yahoo.com

     Domain: outlook.com
       - dave@outlook.com

 Report 2: Personal emails only

     Domain: yahoo.com
       - charlie.personal@yahoo.com

 Report 3: All emails (including invalid)

     Domain: gmail.com
       - alice@gmail.com

     Domain: work.com
       - bob@work.com

     Domain: invalid
       - invalid.email

     Domain: yahoo.com
       - charlie.personal@yahoo.com

     Domain: outlook.com
       - dave@outlook.com

Run test_email_validator.py:

 PYTHONPATH=. pytest tests/test_email_validator.py -vv

Output:

 PYTHONPATH=. pytest tests/test_email_validator.py -vv
 ============================= test session starts ==============================
 platform linux -- Python 3.12.8, pytest-8.4.0, pluggy-1.6.0 -- /usr/bin/python3.12
 cachedir: .pytest_cache
 rootdir: /Path/to/repos/PYTHON-FOUNDATION/core-python
 plugins: anyio-4.9.0
 collected 4 items                                                              

 tests/test_email_validator.py::test_is_valid_email PASSED                [ 25%]
 tests/test_email_validator.py::test_extract_domain PASSED                [ 50%]
 tests/test_email_validator.py::test_generate_report PASSED               [ 75%]
 tests/test_email_validator.py::test_generate_report_edge_cases PASSED    [100%]

 ============================== 4 passed in 0.08s ===============================

Possible Issues

Of email_validator

Invalid Emails: Handled by is_valid_email() with IndexError` protection.
Empty Inputs: Empty email lists or categories (handled with checks).
Type Hints: Use mypy for static checking:

pip install mypy 
mypy basics/email_validator/main.py

Of Test

Test Failures: Indicate bugs in email_validator/main.py (e.g., incorrect domain extraction).
Module Import Errors: Ensure basics/email_validator/main.py exists; fix path if ModuleNotFoundError occurs.
Incomplete Coverage: Tests cover main cases but not every scenario (e.g., very long emails); add more as needed.
Pytest Setup: Ensure pytest is installed; update requirements.txt if missed.

Functions demonstrates decorators and lambda functions.

Links

Github: Repo - Python Foundation/email_validator

Click here for: Project list

🤝 How to Contribute / Follow Along

Clone the repo or copy scripts to try on your own machine.
Share your output or improvements in the comments.
DM me on GitHub or Hashnode for feedback!

📢 Let’s Connect

Follow me on Hashnode to get notified when I publish new Python projects 👇

➡️ Chetan Tekam

Build a Email Validator in Python

Table of contents

What new Concept covered

`*args` (Variable Positional Arguments):

`**kwargs` (Variable Keyword Arguments):

String Manipulation:

Nested Loops and `any()`:

Pytest:

Test Functions:

Importing Modules:

Project summary

Structure

How I Built it

How to run

Possible Issues

Of email_validator

Of Test

Next

Links

🤝 How to Contribute / Follow Along

📢 Let’s Connect

Subscribe to my newsletter

Chetan Tekam

Chetan Tekam

Build a Email Validator in Python

Table of contents

What new Concept covered

*args (Variable Positional Arguments):

**kwargs (Variable Keyword Arguments):

String Manipulation:

Nested Loops and any():

Pytest:

Test Functions:

Importing Modules:

Project summary

Structure

How I Built it

How to run

Possible Issues

Of email_validator

Of Test

Next

Links

🤝 How to Contribute / Follow Along

📢 Let’s Connect

Subscribe to my newsletter

Chetan Tekam

Chetan Tekam

`*args` (Variable Positional Arguments):

`**kwargs` (Variable Keyword Arguments):

Nested Loops and `any()`: