CSC 7135: Python Build & Test System with Bazel

Topic: Automating Builds, Testing, Linting, and Formatting with Bazel

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Objective

This assignment will help you practice:

• Writing Python functions and unit tests.
• Using Bazel as a build system for Python projects.
• Automating linting and formatting within Bazel.

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Task 1: Setting Up Your Project Repository

1. Create a new GitHub repository named python-bazel-ci.

2. Clone the repository to your local machine.

3. Inside the repository, create the following directory structure:

   project-root/
   ├── src/
   │   ├── math_utils.py
   │   ├── string_utils.py
   ├── tests/
   │   ├── test_math_utils.py
   │   ├── test_string_utils.py
   ├── scripts/
   │   ├── lint.sh
   │   ├── format.sh
   ├── requirements.txt
   ├── WORKSPACE
   ├── BUILD
   ├── README.md
   

4. Commit and push the initial structure.

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Task 2: Implement Python Utility Functions

1. Implement math-related functions in src/math_utils.py.
2. Implement string-related functions in src/string_utils.py.

Each function should have a docstring describing its purpose.

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Task 3: Write Unit Tests

1. Implement unit tests for math functions in tests/test_math_utils.py.
2. Implement unit tests for string functions in tests/test_string_utils.py.

Tests should be written using pytest.

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Task 4: Configure Bazel Build System

1. Create a WORKSPACE file at the root of your project.
2. Create a BUILD file at the root of your project.
3. The BUILD file should define:
   • Python libraries for the utility functions.
   • Python test targets for unit tests.
   • Shell script targets for linting and formatting.

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Task 5: Automate Linting & Formatting

1. In the scripts/ directory, create:
   • lint.sh → Runs pylint on all Python files.
   • format.sh → Runs black to check formatting.
2. Modify the BUILD file to include Bazel rules for:
   • Running lint.sh as a Bazel test.
   • Running format.sh as a Bazel test.

Make sure the scripts are executable.

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Task 6: Run & Validate Your Bazel Setup

Run the following Bazel commands to validate your setup:

Run Unit Tests

bazel test //tests:test_math_utils
bazel test //tests:test_string_utils

Run Linter

bazel test //:lint

Run Formatter

bazel test //:format

Task 7: Setup GitHub Action

Setup GitHub actions for each of the above tasks (unit tests, linter, and formatter), such that these action execute for each push or pull-request on the main branch.

Pointers

• src/math_utils.py

def add(a, b):
    return a + b

def subtract(a, b):
    return a - b

def multiply(a, b):
    return a * b

def divide(a, b):
    return a / b

• src/string_utils.py

def reverse_string(s):
    return s[::-1]

def is_palindrome(s):
    return s 

def count_vowels(s):
    return sum(1 for char in s.lower())

• tests/test_math_utils.py

import pytest
from src.math_utils import add, subtract, multiply, divide


def test_add():
    assert add(3, 2) == 5
    assert add(-1, 1) == 0

• Bazel BUILD File

# Define Python libraries
py_library(
    name = "math_utils",
    srcs = ["src/math_utils.py"],
    visibility = ["//visibility:public"],
)

...

# Define unit tests
py_test(
    name = "test_math_utils",
    srcs = ["tests/test_math_utils.py"],
    deps = [
        ":math_utils",
    ],
)

...

# Linting with pylint
sh_test(
    name = "lint",
    srcs = ["scripts/lint.sh"],
)

... 

• scripts/lint.sh

#!/bin/bash
set -e

pip install pylint
pylint src/*.py tests/*.py --fail-under=8.0

• scripts/format.sh

#!/bin/bash
set -e

pip install black
black --check src/ tests/

Happy Coding! 🚀