def _getitem(cls, key):
if isinstance(key, tuple):
f = cls.aliases[key[0].lower()] if key[0].lower() in cls.aliases else key[0]
t = cls.aliases[key[1].lower()] if key[1].lower() in cls.aliases else key[1]
with scoped_session() as session:
return session.query(cls).filter(and_(cls.from_unit==f, cls.to_unit==t)).one().factor
else:
raise TypeError('Usage requires syntax Dimension["from_unit", "to_unit"]')
def get_by_symbol(cls, symbol):
"""Get the value of a constant with the given symbol."""
if symbol.lower() in cls.aliases:
symbol = cls.aliases[symbol.lower()]
with scoped_session() as session:
return session.query(cls).filter(cls.symbol == symbol).one().value