Question

I use python only occasionally, sorry for a seemingly trivial question

>>> a = set(((1,1),(1,6),(6,1),(6,6)))
>>> a
set([(6, 1), (1, 6), (1, 1), (6, 6)])
>>> a - set(((1,1)))
set([(6, 1), (1, 6), (1, 1), (6, 6)])
>>> a.remove((1,1))
>>> a
set([(6, 1), (1, 6), (6, 6)])

why ‘-‘ operator didn’t delete the element but the remove did ?

Answer 1

Because you missed a comma:

>>> set(((1,1)))
set([1])

should be:

>>> set(((1,1),))
set([(1, 1)])

or, to be more readable:

set([(1,1)])

or even (Py2.7+):

{(1,1)}