@classmethod<EOL><INDENT>def load_system(cls, dict_, system_id='<STR_LIT>'):<DEDENT>
obj = cls()<EOL>obj.system = dict_<EOL>obj.system_id = system_id<EOL>return obj<EOL>
Create a :class:`MolecularSystem` from a python :class:`dict`.

As the loaded :class:`MolecularSystem` is storred as a :class:`dict` in
the :class:`MolecularSystem.system` it can also be loaded directly from
a :class:`dict` input. This feature is used by :mod:`trajectory` that
extracts trajectory frames as dictionaries and returns them
as :class:`MolecularSystem` objects through this classmethod.

Parameters
----------
dict_ : :class:`dict`
   A python dictionary.

system_id : :class:`str` or :class:'int', optional
   Inherited or user defined system id. (default='system')

Returns
-------
:class:`pywindow.molecular.MolecularSystem`
    :class:`MolecularSystem`