How to use the virtualenv.main function in virtualenv

def create_virtualenv(where, distribute=False):
    save_argv = sys.argv

    try:
        import virtualenv
        distribute_opt = distribute and ['--distribute'] or []
        sys.argv = ['virtualenv', '--quiet'] + distribute_opt + ['--no-site-packages', '--unzip-setuptools', where]
        virtualenv.main()
    finally:
        sys.argv = save_argv

    return virtualenv.path_locations(where)

def create_virtualenv(venv_name, dir_path=None):
    dir_path = dir_path or tempfile.mkdtemp()
    old_args = sys.argv
    try:
        from virtualenv import main
        sys.argv = ['virtualenv', op.join(dir_path, venv_name)]
        main()
    finally:
        sys.argv = old_args
    print("Created virtualenv %s at %s" % (venv_name, dir_path))
    return dir_path

if not os.path.isdir(TARGET_DIR):
        sys.exit('Existing non-directory found at: {}'.format(TARGET_DIR))
else:
    os.mkdir(TARGET_DIR)

if os.path.exists(VENV_DIR):
    shutil.rmtree(VENV_DIR)

if os.path.exists(TMP_DIR):
    shutil.rmtree(TMP_DIR)

original = sys.argv
sys.argv = ['', VENV_DIR]
try:
    sys_stdout.write('creating virtualenv {}\n'.format(VENV_DIR).encode())
    virtualenv.main()
finally:
    sys.argv = original


if platform.system() == 'Windows':
    pip_exe = os.path.join(VENV_DIR, 'Scripts', 'pip.exe')
    deps_dir = os.path.join(VENV_DIR, 'Lib', 'site-packages')
else:
    pip_exe = os.path.join(VENV_DIR, 'bin', 'pip')
    python_dir = os.listdir(os.path.join(VENV_DIR, 'lib'))[0]
    deps_dir = os.path.join(VENV_DIR, 'lib', python_dir, 'site-packages')

if not os.path.isfile(pip_exe):
    sys.exit('Pip not found in: {}'.format(pip_exe))

for req_file in REQ_FILES:

if reason:
                info('Removing invalidated virtualenv. (%s)' % reason)
                run(('rm', '-rf', venv_path))
            else:
                info('Keeping valid virtualenv from previous run.')
                raise SystemExit(0)  # looks good! we're done here.

    # this is actually a documented extension point:
    #   http://virtualenv.readthedocs.org/en/latest/reference.html#adjust_options
    import virtualenv
    virtualenv.adjust_options = adjust_options

    from sys import argv
    argv[:] = ('virtualenv',) + args
    info(colorize(argv))
    raise_on_failure(virtualenv.main)
    # There might not be a venv_path if doing something like "venv= --version"
    # and not actually asking virtualenv to make a venv.
    if return_values.venv_path is not None:
        run(('rm', '-rf', join(return_values.venv_path, 'local')))

def create_virtual_env(project_path, install_path, ve_args):
    # remove existing virtual env if exists
    ve_path = os.path.join(project_path, cfg.VIRTUAL_ENV_PATH)
    if os.path.exists(ve_path):
        shutil.rmtree(ve_path)
    try:
        logger.info('creating virtual env')
        sys.argv = ['']
        if '--no-wheel' not in ve_args:
            sys.argv.append('--no-wheel')

        sys.argv.extend(ve_args)
        sys.argv.append(ve_path)
        try:
            virtualenv.main()
        except SystemExit as sysext:
            if sysext.code != 0:
                raise SystemExit(sysext)
    except Exception:
        logger.exception('failed to create virtualenv: ')
        raise Exception('failed to create virtualenv!')

    try:
        logger.info('installing requirements for virtualenv')
        # update pip to latest version
        run_command(['{}/{}/bin/pip'.format(project_path,
                                            cfg.VIRTUAL_ENV_PATH),
                     'install',
                     '-U',
                     'pip'])

def run(inst):
    virtualenv.after_install = inst.after_install
    virtualenv.adjust_options = inst.adjust_options
    virtualenv.main()    

def run():
    virtualenv.after_install = after_install
    virtualenv.adjust_options = adjust_options
    virtualenv.main()