Use pip to find pip installed packages in a given prefix.

def main():
    """Use pip to find pip installed packages in a given prefix."""
    pip_packages = {}
    for package in pip.get_installed_distributions():
        name = package.project_name
        version = package.version
        full_name = "{0}-{1}-pip".format(name.lower(), version)
        pip_packages[full_name] = {'version': version}
    data = json.dumps(pip_packages)
    print(data)