How to Create a Git Branch if it Doesn't Exist in Python

import subprocess
import sys

def ensure_branch(branch_name):
    """Create a Git branch if it doesn't exist, otherwise checkout it."""
    try:
        # Check if the branch exists locally
        result = subprocess.run(
            ["git", "branch", "--list", branch_name],
            capture_output=True,
            text=True,
            check=True
        )
        
        if not result.stdout.strip():
            # Branch doesn't exist — create and switch to it
            subprocess.run(
                ["git", "checkout", "-b", branch_name],
                check=True
            )
            action = "created"
        else:
            # Branch exists — switch to it
            subprocess.run(
                ["git", "checkout", branch_name],
                check=True
            )
            action = "switched to existing"
        
        return f"Branch '{branch_name}' {action} successfully"
    except subprocess.CalledProcessError as e:
        return f"Error: {e}"

if __name__ == "__main__":
    branch = "feature/mock-implementation"
    print(ensure_branch(branch))