Python: See if one set contains another entirely?

Question

Is there a fast way to check if one set entirely contains another?

Something like:

>>>[1, 2, 3].containsAll([2, 1])
True

>>>[1, 2,         


        

Answer 1

One option is left untouched -- subtraction:

>>> {1, 2} - {1, 2, 3}
set([])
>>> {1, 2, 3} - {1, 2}
set([3])

Basically you check what elements in first list are not in second list.

I found it very handy since you could show what values are missing:

>>> def check_contains(a, b):
...     diff = a - b
...     if not diff:
...         # All elements from a are present in b
...         return True
...     print('Some elements are missing: {}'.format(diff))
...     return False
...
>>> check_contains({1, 2}, {1, 2, 3})
True
>>> check_contains({1, 2, 3}, {1, 2})
Some elements are missing: set([3])
False