How to Create an App Using Python (CLI, Desktop and Web)

Here’s how to create an app using Python: decide what kind of app it is (command line, desktop or web), pick the matching library, and build a small working version first. For a desktop window, PyQt6 takes about 30 lines:

python -m pip install PyQt6      # desktop apps
python -m pip install flask      # web apps

To keep things comparable, I built the same tip calculator three ways and ran each one on Python 3.12.5, Flask 3.1.3 and PyQt6. The screenshots are the real apps running on Windows.

You’ll see a command-line app with argparse, a desktop app with PyQt6, a web app with Flask, how to test it, and how to package an app so others can run it.

Which kind of Python app should you build?

App type	Library	Good for
Command line (CLI)	argparse (built in), Typer, Click	Scripts and tools for yourself or developers
Desktop (GUI)	Tkinter (built in), PyQt6 / PySide6	Windows, Mac and Linux programs with windows and buttons
Web	Flask, Django, FastAPI	Anything people use in a browser
Data apps	Streamlit	Dashboards from data scripts, quickly
Mobile	Kivy, BeeWare	Possible, but Python is rarely the first choice for phones

1. Create a command-line app with argparse

A command-line app is the quickest to build. argparse turns command arguments into Python values and writes the --help text for you:

import argparse

def split_bill(bill, tip_pct, people):
    total = bill * (1 + tip_pct / 100)
    return round(total, 2), round(total / people, 2)

parser = argparse.ArgumentParser(description="Split a restaurant bill with tip.")
parser.add_argument("bill", type=float, help="bill amount in dollars")
parser.add_argument("--tip", type=float, default=18, help="tip percent (default 18)")
parser.add_argument("--people", type=int, default=1, help="number of people")
args = parser.parse_args()

total, each = split_bill(args.bill, args.tip, args.people)
print(f"Total with {args.tip:g}% tip: ${total:,.2f}")
print(f"Each of {args.people} pays: ${each:,.2f}")

Output:

Total with 20% tip: $101.40
Each of 3 pays: $33.80
usage: tipcalc.py [-h] [--tip TIP] [--people PEOPLE] bill

Split a restaurant bill with tip.

positional arguments:
  bill             bill amount in dollars

options:
  -h, --help       show this help message and exit
  --tip TIP        tip percent (default 18)
  --people PEOPLE  number of people

More on reading arguments in Python command-line arguments.

2. Create a desktop app with PyQt6

For a real window with text boxes and a button, PyQt6 is a solid choice. The class builds a form; clicking the button runs calculate():

import sys
from PyQt6.QtWidgets import QApplication, QFormLayout, QLabel, QLineEdit, QPushButton, QWidget

class TipCalculator(QWidget):
    def __init__(self):
        super().__init__()
        self.setWindowTitle("Tip Calculator")
        self.bill, self.tip, self.people = QLineEdit("84.50"), QLineEdit("20"), QLineEdit("3")
        self.result = QLabel("")
        button = QPushButton("Calculate")
        button.clicked.connect(self.calculate)

        form = QFormLayout(self)
        form.addRow("Bill ($):", self.bill)
        form.addRow("Tip (%):", self.tip)
        form.addRow("People:", self.people)
        form.addRow(button)
        form.addRow(self.result)
        self.resize(320, 200)
        self.calculate()

    def calculate(self):
        try:
            total = float(self.bill.text()) * (1 + float(self.tip.text()) / 100)
            each = total / int(self.people.text())
            self.result.setText(f"Total ${total:,.2f}  |  Each ${each:,.2f}")
        except ValueError:
            self.result.setText("Please enter numbers only.")

app = QApplication(sys.argv)
window = TipCalculator()
window.show()
app.exec()

Tkinter comes with Python and is fine for simple tools; PyQt6 looks more polished and scales to bigger apps. See Python GUI programming for a broader overview.

3. Create a web app with Flask

A web app runs in any browser, with nothing to install for your users. Flask maps a URL to a Python function that returns HTML:

from flask import Flask, request

app = Flask(__name__)

PAGE = """<!doctype html><title>Tip Calculator</title>
<body style="font-family:Segoe UI,Arial;max-width:420px;margin:40px auto">
<h2>Tip Calculator</h2>
<form>
  <p>Bill ($) <input name="bill" value="{bill}"></p>
  <p>Tip (%) <input name="tip" value="{tip}"></p>
  <p>People <input name="people" value="{people}"></p>
  <button>Calculate</button>
</form>
<p style="font-size:20px"><b>{result}</b></p>
</body>"""

@app.route("/")
def home():
    bill = request.args.get("bill", "84.50")
    tip = request.args.get("tip", "20")
    people = request.args.get("people", "3")
    try:
        total = float(bill) * (1 + float(tip) / 100)
        result = f"Total ${total:,.2f} | Each ${total / int(people):,.2f}"
    except ValueError:
        result = "Please enter numbers only."
    return PAGE.format(bill=bill, tip=tip, people=people, result=result)

if __name__ == "__main__":
    app.run(port=5057)

Run it with python tipweb.py and open http://127.0.0.1:5057. Here’s the page from my local run:

How do you test a Python app?

Flask’s test client calls your routes without starting a server, so you can check results and error handling in a normal script or test suite:

from tipweb import app

client = app.test_client()                   # call the app without starting a server
resp = client.get("/?bill=120&tip=18&people=4")
print("status:", resp.status_code)
html = resp.get_data(as_text=True)
print(html[html.index("Total"):html.index("</b>")])
print(client.get("/?bill=abc").get_data(as_text=True).count("numbers only"), "error message shown for bad input")

Output:

status: 200
Total $141.60 | Each $35.40
1 error message shown for bad input

I’d add tests like this before sharing any app. For a broader look at checking code, see best AI for Python code, which includes a pytest example.

Sharing your Python app

• Desktop: bundle it into a single .exe with PyInstaller; see converting a Python file to an exe.
• Web: deploy to a host such as Render, Railway, PythonAnywhere or a cloud provider, behind a production server like Gunicorn or Waitress.
• Command line: publish it as a package, or share the script with a requirements.txt; see pip install -r requirements.txt.

Helpful guides for your first Python app:

• How to run a Python script
• Python virtual environments
• Import from another directory
• Types of errors in Python

Frequently asked questions