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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def pip_create_virtualenv(path=None):
 """Create an isolated Python environment."""

    if six.PY2:
        apt_install('python-virtualenv')
    else:
        apt_install('python3-virtualenv')

    if path:
        venv_path = path
    else:
        venv_path = os.path.join(charm_dir(), 'venv')

    if not os.path.exists(venv_path):
        subprocess.check_call(['virtualenv', venv_path])