Project: Package-Ready Mini App in Python0%

Project: Package-Ready Mini App in Python

Intermediate8 min read•Updated: 2026-10-01

Project: Package-Ready Mini App

In this capstone project, we will apply the software packaging and environment concepts covered across this chapter—Virtual Environments, Pip Management, Dependency Manifests, and PEP 621 Standard Packaging—to structure, package, and install a professional, distributable Command-Line Currency Converter Tool.

1. Professional Project Directory Layout

A production-ready Python project follows a standardized folder hierarchy that separates application source code, tests, documentation, and configuration files:

1currency_converter_app/
├── .gitignore                  # Prevents committing .venv and caches
├── README.md                   # Project documentation and quickstart
├── requirements.txt            # Pinned runtime dependencies
├── requirements-dev.txt        # Development dependencies (pytest, black)
├── pyproject.toml              # Modern Python packaging configuration (PEP 621)
├── currency_converter/         # Core application package
│    ├── __init__.py            # Package marker & version definition
│    ├── api_client.py          # Network API interactions
│    └── cli.py                 # Command-line interface & argument parser
└── tests/                      # Automated test suite
    └── test_converter.py

2. Defining Dependencies: `requirements.txt` & `.gitignore`

`.gitignore`

1.venv/
2venv/
3__pycache__/
4*.pyc
5*.egg-info/
6dist/
7build/
8.pytest_cache/

`requirements.txt`

1requests==2.31.0

`requirements-dev.txt`

1-r requirements.txt
2pytest==8.2.0
3flake8==7.0.0

3. Application Source Code

`currency_converter/init.py`

1"""Currency Converter Package."""
2__version__ = "1.0.0"

`currency_converter/api_client.py`

1import requests
2from typing import Dict, Optional
3 
4 
5class CurrencyAPI:
  """Fetches real-time exchange rates from public API."""
  
  BASE_URL = "https://api.frankfurter.app/latest"
9 
  @classmethod
  def get_rate(cls, base: str, target: str) -> Optional[float]:
      params = {"from": base.upper(), "to": target.upper()}
      try:
          response = requests.get(cls.BASE_URL, params=params, timeout=5)
          response.raise_for_status()
          data = response.json()
          return data["rates"][target.upper()]
      except (requests.RequestException, KeyError) as err:
          print(f"[API Error] Failed to fetch rate: {err}")
          return None

`currency_converter/cli.py`

1import sys
2from currency_converter.api_client import CurrencyAPI
3 
4 
5def convert(amount: float, base: str, target: str):
6    base = base.upper()
7    target = target.upper()
8    
9    print(f"\nFetching live conversion rate from {base} to {target}...")
10    rate = CurrencyAPI.get_rate(base, target)
11    
12    if rate is None:
13        print("Conversion failed. Please verify currency codes (e.g. USD, EUR, INR, GBP).")
14        return
15 
16    converted_amount = amount * rate
17    print("=" * 45)
18    print(f" {amount:,.2f} {base} = {converted_amount:,.2f} {target}")
19    print(f" Exchange Rate: 1 {base} = {rate:.4f} {target}")
20    print("=" * 45)
21 
22 
23def main():
24    if len(sys.argv) != 4:
25        print("Usage: currency-convert <amount> <base_currency> <target_currency>")
26        print("Example: currency-convert 100 USD INR")
27        sys.exit(1)
28 
29    try:
30        amount = float(sys.argv[1])
31    except ValueError:
32        print(f"Error: Invalid amount '{sys.argv[1]}'. Must be a numeric value.")
33        sys.exit(1)
34 
35    base = sys.argv[2]
36    target = sys.argv[3]
37 
38    convert(amount, base, target)
39 
40 
41if __name__ == "__main__":
42    main()

4. Modern Packaging Manifest: `pyproject.toml`

The pyproject.toml file is the unified standard configuration for Python packaging, replacing legacy setup.py scripts:

1[build-system]
2requires = ["setuptools>=61.0"]
3build-backend = "setuptools.build_meta"
4 
5[project]
6name = "currency-converter-cli"
7version = "1.0.0"
8authors = [
9  { name = "MSK Student Developer", email = "student@mskinstitute.com" },
10]
11description = "A clean CLI currency converter using real-time open exchange rates"
12readme = "README.md"
13requires-python = ">=3.8"
14dependencies = [
15    "requests>=2.28.0",
16]
17 
18# Defines command-line executable installed globally into the environment!
19[project.scripts]
20currency-convert = "currency_converter.cli:main"

5. Installing in Editable Mode (`pip install -e .`)

During development, install your package into your active virtual environment in Editable Mode (-e). This registers the package and its console scripts while linking directly to your source files, meaning edits to code take effect immediately without re-installing:

1# 1. Activate your virtual environment
2source .venv/bin/activate  # On Windows: .venv\Scripts\Activate.ps1
3 
4# 2. Install package locally in editable mode
5python -m pip install -e .
6 
7# 3. The CLI command is now available as a terminal utility!
8currency-convert 100 USD INR

Output:

1Fetching live conversion rate from USD to INR...
2=============================================
3 100.00 USD = 8,365.20 INR
4 Exchange Rate: 1 USD = 83.6520 INR
5=============================================

⚠️ Common Intermediate Mistakes & Gotchas

1. Hardcoding Absolute System Paths

Hardcoding paths like C:\Users\Sumit\project\data.json will break as soon as another developer clones your project. Use relative paths derived from __file__.

2. Missing `.gitignore` File

Always create a clean .gitignore including __pycache__/, .venv/, and *.pyc before publishing your project repository.

💻 Try It Yourself: Extension Challenge - Setup Script

Challenge

Create a basic setup.py or pyproject.toml configuration that makes your package installable in editable mode using pip install -e ..

Complete Solution

1# pyproject.toml
2"""
3[build-system]
4requires = ["setuptools>=61.0"]
5build-backend = "setuptools.build_meta"
6 
7[project]
8name = "msk_utility_tool"
9version = "1.0.0"
10authors = [{ name="MSK Institute" }]
11description = "Production utility package"
12dependencies = [
13    "requests>=2.31.0",
14]
15"""
16print("Created standard modern pyproject.toml for editable pip install.")

Interactive Quiz• Knowledge Check

Practice Quiz

Question 1

What does the -e flag stand for in pip install -e .?

Question 2

Which modern configuration file has become the standardized replacement for setup.py under PEP 518/621?

Question 3

In pyproject.toml, what does [project.scripts] define?

Question 4

Why is having an __init__.py file inside the currency_converter folder important?

Question 5

What file should always be included in version control to inform team members of the exact dependency versions required?

🚀 What's Next?

In the next lesson, we will continue your intermediate Python journey with Introduction to Matplotlib (13: Data Visualization Basics).

👉 Continue to Next Lesson: Introduction to Matplotlib →

Next Lesson

Introduction to Matplotlib

Continue learning with hands-on practice, examples, and exercises in the upcoming topic.

Related Lessons

Previous Lesson	Next Lesson
Requirements.txt	Introduction to Matplotlib

Practice Quiz

Test your understanding of this lesson with 5 questions. Each question has one correct answer.

Previous Next

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Introduction to Matplotlib

Project: Package-Ready Mini App in Python

Intermediate8 min read•Updated: 2026-10-01

Study Materials Cheatsheet

Project: Package-Ready Mini App

1. Professional Project Directory Layout

A production-ready Python project follows a standardized folder hierarchy that separates application source code, tests, documentation, and configuration files:

1currency_converter_app/
├── .gitignore                  # Prevents committing .venv and caches
├── README.md                   # Project documentation and quickstart
├── requirements.txt            # Pinned runtime dependencies
├── requirements-dev.txt        # Development dependencies (pytest, black)
├── pyproject.toml              # Modern Python packaging configuration (PEP 621)
├── currency_converter/         # Core application package
│    ├── __init__.py            # Package marker & version definition
│    ├── api_client.py          # Network API interactions
│    └── cli.py                 # Command-line interface & argument parser
└── tests/                      # Automated test suite
    └── test_converter.py

2. Defining Dependencies: `requirements.txt` & `.gitignore`

`.gitignore`

1.venv/
2venv/
3__pycache__/
4*.pyc
5*.egg-info/
6dist/
7build/
8.pytest_cache/

`requirements.txt`

1requests==2.31.0

`requirements-dev.txt`

1-r requirements.txt
2pytest==8.2.0
3flake8==7.0.0

3. Application Source Code

`currency_converter/init.py`

1"""Currency Converter Package."""
2__version__ = "1.0.0"

`currency_converter/api_client.py`

1import requests
2from typing import Dict, Optional
3 
4 
5class CurrencyAPI:
  """Fetches real-time exchange rates from public API."""
  
  BASE_URL = "https://api.frankfurter.app/latest"
9 
  @classmethod
  def get_rate(cls, base: str, target: str) -> Optional[float]:
      params = {"from": base.upper(), "to": target.upper()}
      try:
          response = requests.get(cls.BASE_URL, params=params, timeout=5)
          response.raise_for_status()
          data = response.json()
          return data["rates"][target.upper()]
      except (requests.RequestException, KeyError) as err:
          print(f"[API Error] Failed to fetch rate: {err}")
          return None

`currency_converter/cli.py`

1import sys
2from currency_converter.api_client import CurrencyAPI
3 
4 
5def convert(amount: float, base: str, target: str):
6    base = base.upper()
7    target = target.upper()
8    
9    print(f"\nFetching live conversion rate from {base} to {target}...")
10    rate = CurrencyAPI.get_rate(base, target)
11    
12    if rate is None:
13        print("Conversion failed. Please verify currency codes (e.g. USD, EUR, INR, GBP).")
14        return
15 
16    converted_amount = amount * rate
17    print("=" * 45)
18    print(f" {amount:,.2f} {base} = {converted_amount:,.2f} {target}")
19    print(f" Exchange Rate: 1 {base} = {rate:.4f} {target}")
20    print("=" * 45)
21 
22 
23def main():
24    if len(sys.argv) != 4:
25        print("Usage: currency-convert <amount> <base_currency> <target_currency>")
26        print("Example: currency-convert 100 USD INR")
27        sys.exit(1)
28 
29    try:
30        amount = float(sys.argv[1])
31    except ValueError:
32        print(f"Error: Invalid amount '{sys.argv[1]}'. Must be a numeric value.")
33        sys.exit(1)
34 
35    base = sys.argv[2]
36    target = sys.argv[3]
37 
38    convert(amount, base, target)
39 
40 
41if __name__ == "__main__":
42    main()

4. Modern Packaging Manifest: `pyproject.toml`

The pyproject.toml file is the unified standard configuration for Python packaging, replacing legacy setup.py scripts:

1[build-system]
2requires = ["setuptools>=61.0"]
3build-backend = "setuptools.build_meta"
4 
5[project]
6name = "currency-converter-cli"
7version = "1.0.0"
8authors = [
9  { name = "MSK Student Developer", email = "student@mskinstitute.com" },
10]
11description = "A clean CLI currency converter using real-time open exchange rates"
12readme = "README.md"
13requires-python = ">=3.8"
14dependencies = [
15    "requests>=2.28.0",
16]
17 
18# Defines command-line executable installed globally into the environment!
19[project.scripts]
20currency-convert = "currency_converter.cli:main"

5. Installing in Editable Mode (`pip install -e .`)

1# 1. Activate your virtual environment
2source .venv/bin/activate  # On Windows: .venv\Scripts\Activate.ps1
3 
4# 2. Install package locally in editable mode
5python -m pip install -e .
6 
7# 3. The CLI command is now available as a terminal utility!
8currency-convert 100 USD INR

Output:

1Fetching live conversion rate from USD to INR...
2=============================================
3 100.00 USD = 8,365.20 INR
4 Exchange Rate: 1 USD = 83.6520 INR
5=============================================

⚠️ Common Intermediate Mistakes & Gotchas

1. Hardcoding Absolute System Paths

Hardcoding paths like C:\Users\Sumit\project\data.json will break as soon as another developer clones your project. Use relative paths derived from __file__.

2. Missing `.gitignore` File

Always create a clean .gitignore including __pycache__/, .venv/, and *.pyc before publishing your project repository.

💻 Try It Yourself: Extension Challenge - Setup Script

Challenge

Create a basic setup.py or pyproject.toml configuration that makes your package installable in editable mode using pip install -e ..

Complete Solution

1# pyproject.toml
2"""
3[build-system]
4requires = ["setuptools>=61.0"]
5build-backend = "setuptools.build_meta"
6 
7[project]
8name = "msk_utility_tool"
9version = "1.0.0"
10authors = [{ name="MSK Institute" }]
11description = "Production utility package"
12dependencies = [
13    "requests>=2.31.0",
14]
15"""
16print("Created standard modern pyproject.toml for editable pip install.")

Interactive Quiz• Knowledge Check

Practice Quiz

Question 1

What does the -e flag stand for in pip install -e .?

Question 2

Which modern configuration file has become the standardized replacement for setup.py under PEP 518/621?

Question 3

In pyproject.toml, what does [project.scripts] define?

Question 4

Why is having an __init__.py file inside the currency_converter folder important?

Question 5

What file should always be included in version control to inform team members of the exact dependency versions required?

🚀 What's Next?

In the next lesson, we will continue your intermediate Python journey with Introduction to Matplotlib (13: Data Visualization Basics).

👉 Continue to Next Lesson: Introduction to Matplotlib →

Next Lesson

Introduction to Matplotlib

Continue learning with hands-on practice, examples, and exercises in the upcoming topic.

Related Lessons

Previous Lesson	Next Lesson
Requirements.txt	Introduction to Matplotlib

Practice Quiz

Test your understanding of this lesson with 5 questions. Each question has one correct answer.

Previous Next

Project: Package-Ready Mini App

1. Professional Project Directory Layout

2. Defining Dependencies: requirements.txt & .gitignore

.gitignore

requirements.txt

requirements-dev.txt

3. Application Source Code

currency_converter/__init__.py

currency_converter/api_client.py

currency_converter/cli.py

4. Modern Packaging Manifest: pyproject.toml

5. Installing in Editable Mode (pip install -e .)

Output:

⚠️ Common Intermediate Mistakes & Gotchas

1. Hardcoding Absolute System Paths

2. Missing .gitignore File

💻 Try It Yourself: Extension Challenge - Setup Script

Challenge

Complete Solution

Practice Quiz

🚀 What's Next?

Introduction to Matplotlib

Related Lessons

Practice Quiz

Loading Page Content...

Project: Package-Ready Mini App

1. Professional Project Directory Layout

2. Defining Dependencies: requirements.txt & .gitignore

.gitignore

requirements.txt

requirements-dev.txt

3. Application Source Code

currency_converter/__init__.py

currency_converter/api_client.py

currency_converter/cli.py

4. Modern Packaging Manifest: pyproject.toml

5. Installing in Editable Mode (pip install -e .)

Output:

⚠️ Common Intermediate Mistakes & Gotchas

1. Hardcoding Absolute System Paths

2. Missing .gitignore File

💻 Try It Yourself: Extension Challenge - Setup Script

Challenge

Complete Solution

Practice Quiz

🚀 What's Next?

Introduction to Matplotlib

Related Lessons

Practice Quiz

2. Defining Dependencies: `requirements.txt` & `.gitignore`

`.gitignore`

`requirements.txt`

`requirements-dev.txt`

`currency_converter/init.py`

`currency_converter/api_client.py`

`currency_converter/cli.py`

4. Modern Packaging Manifest: `pyproject.toml`

5. Installing in Editable Mode (`pip install -e .`)

2. Missing `.gitignore` File

2. Defining Dependencies: `requirements.txt` & `.gitignore`

`.gitignore`

`requirements.txt`

`requirements-dev.txt`

`currency_converter/init.py`

`currency_converter/api_client.py`

`currency_converter/cli.py`

4. Modern Packaging Manifest: `pyproject.toml`

5. Installing in Editable Mode (`pip install -e .`)

2. Missing `.gitignore` File