subtypes.weaktuple

the weaktuple is a tuple with weakened immutability.

the main difference between the two is that the weaktuple’s immutability is only concerned with the size and the underlying type of each component.

in other words, tuple’s immutability property can be viewed as a set of three constraints C = (tupleSize, tupleComponentValue, tupleComponentType) (the third may be somehow implicit). The weaktuple’s set of constraints has only two components: C = (tupleSize,tupleComponentType), equivalent to “tuple has a product type” if you like.

the values of weaktuple’s component can be updated as long as the component’s type and tuple’s size constraints are verified.

applicability: storing the arguments to a function as a tuple for a later function call: while computing a set of conditions, the arguments may be needing updates. It’s easier, clearer and hopefully faster to do an inplace tuple member update:

>>> from subtypes.weaktuple import weaktuple
>>> def f(p1,p2,p3):
...     print "called with:(%r,%r,%r)"%(p1,p2,p3)
...
>>> o=weaktuple([1,'abc',[(1,2),(1,3),(2,3)]])
>>> o
(1, 'abc', [(1, 2), (1, 3),(2, 3)])
>>> f(*o)
called with:(1,'abc',[(1, 2),(1, 3), (2, 3)])
>>> if issubclass(weaktuple,tuple): o[1]='cba'
>>> f(*o)
called with:(1,'cba',[(1,2), (1,3), (2,3)])
>>>

see weaktuple module documentation for additional information

coming up:

• weakbool