How to Check an External Gateway vs Use an Internal Mock in Python

import subprocess
import sys

def check_external_gateway():
    """True if we can reach an external network target."""
    try:
        subprocess.run(
            ["ping", "-c", "1", "-W", "2", "8.8.8.8"],
            capture_output=True,
            timeout=3,
            check=True,
        )
        return True
    except (subprocess.CalledProcessError, subprocess.TimeoutExpired, FileNotFoundError):
        return False

class MockGateway:
    """Deterministic stand-in for external network access during tests."""
    def __init__(self, success=True):
        self.success = success

    def reachable(self):
        return self.success

def main():
    external_available = check_external_gateway()
    mock = MockGateway(success=True)

    print(f"External gateway reachable: {external_available}")
    print(f"Internal mock reachable:    {mock.reachable()}")
    print(f"Using {'EXTERNAL' if external_available else 'MOCK'} gateway")

if __name__ == "__main__":
    main()