☆ Exercise 1

In this exercise we are going to use the a simple statistics library https://github.com/Bristol-Training/demo-stats-lib.Repository: https://github.com/Bristol-Training/demo-stats-lib

Form groups of 3-6 people and assign roles within your group:

• 1 person: Repository Owner (creates fork and manages PRs)
• 1-2 people: Feature Developers A (add std_dev function)
• 1-2 people: Feature Developers B (add NA handling)
• 1-2 people: Code Formatters (apply Black formatting)

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Part 1: Repository Setup

Repository Owner does these steps:

Step 1: Fork the Repository

1. Go to https://github.com/Bristol-Training/demo-stats-lib
2. Click Fork (top-right)
3. This creates a copy under your GitHub account

Step 2: Add Collaborators

1. In your forked repository, go to Settings → Collaborators
2. Click Add people
3. Add each team member by their GitHub username
4. Team members will receive an email invitation they must accept

Step 3: Everyone Clones the Fork

All team members (including owner):

# Replace OWNER-USERNAME with the repository owner's username
git clone https://github.com/OWNER-USERNAME/demo-stats-lib.git
cd demo-stats-lib

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Part 2: Parallel Development

Task A

Objective: Make statistics functions robust to missing values NA.

Task Instructions

Step 1: Create and switch to your feature branch

git checkout main
git pull origin main
git checkout -b feature/na-handling

Step 2: Modify stats_lib.py

Add NA handling to existing functions. For example:

# Filter out None values
clean_data = [x for x in data if x is not None]

Step 3: Update stats_demo.py to test with NA values

# Add test cases with None values
test_data_with_na = [1, 2, None, 4, 5, None, 7]
print(f"Mean (with NAs): {mean(test_data_with_na)}")
print(f"Variance (with NAs): {variance(test_data_with_na)}")

Step 4: Test your changes

python stats_demo.py data/temp1995.csv

Step 5: Commit and push

git add stats_lib.py stats_demo.py
git commit -m "Add NA handling to statistics functions"
git push origin feature/na-handling

Step 6: Create Pull Request

1. Go to GitHub repository

2. Click “Compare & pull request”

3. Title: "Add NA handling to statistics functions"

4. Description:

   ## Changes
   - Added None value filtering to all statistics functions
   - Updated demo.py with NA test cases
   
   ## Testing
   - Tested with datasets containing None values
   - All functions handle empty datasets appropriately

5. Click “Create pull request” (don’t merge yet!)

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Task B

Objective: Add a new standard deviation function to the statistics library.

Task Instructions

Step 1: Create your feature branch

git checkout main
git pull origin main
git checkout -b feature/add-stdev

Step 2: Add the std_dev function to stats_lib.py

You can use:

import math

math.sqrt(variance(data))

Step 3: Update stats_demo.py to demonstrate std_dev

from stats_lib import mean, variance, std_dev

# Demonstrate standard deviation
print("\n--- Standard Deviation ---")
print(f"Standard deviation: {std_dev(data)}")

Step 4: Test your function

python stats_demo.py data/temp1995.csv

You should see the standard deviation calculated for the temperature data.

Step 5: Commit and push

git add stats_lib.py demo.py
git commit -m "Add std_dev function to calculate standard deviation"
git push origin feature/add-stdev

Step 6: Create Pull Request

1. Go to GitHub repository

2. Click “Compare & pull request”

3. Title: "Add standard deviation function"

4. Description:

   ## Changes
   - Added `std_dev(data)` function to statistics.py
   - Function calculates standard deviation as sqrt(variance)
   - Updated stats_demo.py to demonstrate the new function
   
   ## Testing
   - Manually tested with temperature datasets
   - Verified output matches expected results

5. Click “Create pull request” (don’t merge yet!)

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Task C

Objective: Reformat the codebase using Black for consistent style.

Task Instructions

Step 1: Create your feature branch

git checkout main
git pull origin main
git checkout -b style/black-formatting

Step 2: Apply Black formatting to your project

# Format the entire project
black .

# You should see output like:
# reformatted stats_lib.py
# reformatted stats_demo.py
# 2 files reformatted, X files left unchanged

Step 3: Review the changes

git diff

Notice how Black has: - Adjusted line spacing - Reformatted string quotes - Fixed indentation - Wrapped long lines

Step 4: Commit and push

git add .
git commit -m "Apply Black formatting to entire codebase"
git push origin style/black-formatting

Step 5: Create Pull Request

1. Go to GitHub repository

2. Click “Compare & pull request”

3. Title: "Apply Black code formatting"

4. Description:

   ## Changes
   - Applied Black formatter to all Python files
   - Ensures PEP 8 compliance
   - No functional changes, style only
   
   ## Testing
   - Verified all existing tests still pass
   - Code functionality unchanged

5. Click “Create pull request” (don’t merge yet!)

Part 3: The Merge Challenge

Everyone gathers together for this part.

Step 1: Observe the Pull Requests

Repository Owner should now have THREE open pull requests: - feature/na-handling (modifies existing functions + demo.py) - feature/add-stdev (adds new function + demo.py) - style/black-formatting (reformats all files)

All three modified stats_lib.py and demo.py!

Step 2: Merge the First PR

Repository Owner:

1. Choose one PR (e.g., feature/na-handling)
2. Review the changes on GitHub
3. Click “Merge pull request”
4. Click “Confirm merge”
5. Optionally delete the branch

✅ First PR merged successfully!

Step 3: Attempt to Merge the Second PR

Now try to merge the second PR (e.g., feature/add-stdev):

❌ GitHub shows: “This branch has conflicts that must be resolved”

Why conflicts exist:

• stats_lib.py: If Group A modified existing functions and Group B added a new function, there might be conflicts in imports or at the end of the file
• stats_demo.py: Both groups added different test code to the same file