@staticmethod
def list_package_dependency_versions():
    """
        Lists package dependency versions.

        ..  container:: example

            >>> abjad_configuration = abjad.AbjadConfiguration()
            >>> abjad_configuration.list_package_dependency_versions() # doctest: +SKIP
            {'sphinx': '1.1.2', 'pytest': '2.1.2'}

        Returns dictionary.
        """
    dependencies = {}
    dependencies['configobj'] = None
    try:
        import configobj
        dependencies['configobj'] = configobj.__version__
    except (AttributeError, ImportError):
        pass
    dependencies['ply'] = None
    try:
        from ply import lex
        dependencies['ply'] = lex.__version__
    except ImportError:
        pass
    dependencies['pytest'] = None
    try:
        import pytest
        dependencies['pytest'] = pytest.__version__
    except ImportError:
        pass
    dependencies['sphinx'] = None
    try:
        import sphinx
        dependencies['sphinx'] = sphinx.__version__
    except ImportError:
        pass
    return dependencies
