import bpy

filepath = "//link_library.blend"

# load a single scene we know the name of.
with bpy.data.libraries.load(filepath) as (data_from, data_to):
    data_to.scenes = ["Scene"]


# load all meshes
with bpy.data.libraries.load(filepath) as (data_from, data_to):
    data_to.meshes = data_from.meshes


# link all objects starting with 'A'
with bpy.data.libraries.load(filepath, link=True) as (data_from, data_to):
    data_to.objects = [name for name in data_from.objects if name.startswith("A")]


# append everything
with bpy.data.libraries.load(filepath) as (data_from, data_to):
    for attr in dir(data_to):
        setattr(data_to, attr, getattr(data_from, attr))


# the 'data_to' variables lists are
with bpy.data.libraries.load(filepath) as (data_from, data_to):
    data_to.scenes = ["Scene"]


# the loaded objects can be accessed from 'data_to' outside of the context
# since loading the data replaces the strings for the datablocks or None
# if the datablock could not be loaded.
with bpy.data.libraries.load(filepath) as (data_from, data_to):
    data_to.meshes = data_from.meshes
# now operate directly on the loaded data
for mesh in data_to.meshes:
    if mesh is not None:
        print(mesh.name)