Function as_interface

lib/sqlalchemy/util/langhelpers.py:1055–1138

Ensure basic interface compliance for an instance or dict of callables. Checks that ``obj`` implements public methods of ``cls`` or has members listed in ``methods``. If ``required`` is not supplied, implementing at least one interface method is sufficient. Methods present on ``obj`` th

(obj, cls=None, methods=None, required=None)

def as_interface(obj, cls=None, methods=None, required=None):
    """Ensure basic interface compliance for an instance or dict of callables.

    Checks that ``obj`` implements public methods of ``cls`` or has members
    listed in ``methods``. If ``required`` is not supplied, implementing at
    least one interface method is sufficient. Methods present on ``obj`` that
    are not in the interface are ignored.

    If ``obj`` is a dict and ``dict`` does not meet the interface
    requirements, the keys of the dictionary are inspected. Keys present in
    ``obj`` that are not in the interface will raise TypeErrors.

    Raises TypeError if ``obj`` does not meet the interface criteria.

    In all passing cases, an object with callable members is returned.  In the
    simple case, ``obj`` is returned as-is; if dict processing kicks in then
    an anonymous class is returned.

    obj
      A type, instance, or dictionary of callables.
    cls
      Optional, a type.  All public methods of cls are considered the
      interface.  An ``obj`` instance of cls will always pass, ignoring
      ``required``..
    methods
      Optional, a sequence of method names to consider as the interface.
    required
      Optional, a sequence of mandatory implementations. If omitted, an
      ``obj`` that provides at least one interface method is considered
      sufficient.  As a convenience, required may be a type, in which case
      all public methods of the type are required.

    """
    if not cls and not methods:
        raise TypeError("a class or collection of method names are required")

    if isinstance(cls, type) and isinstance(obj, cls):
        return obj

    interface = set(methods or [m for m in dir(cls) if not m.startswith("_")])
    implemented = set(dir(obj))

    complies = operator.ge
    if isinstance(required, type):
        required = interface
    elif not required:
        required = set()
        complies = operator.gt
    else:
        required = set(required)

    if complies(implemented.intersection(interface), required):
        return obj

    # No dict duck typing here.
    if not isinstance(obj, dict):
        qualifier = complies is operator.gt and "any of" or "all of"
        raise TypeError(