For sets, <
is used to test if a set A is a proper subset of set B. For example,
In [147]: set('ab') < set('abc')
Out[147]: True
because set('ab')
is a proper subset of set('abc')
. In contrast,
In [149]: set('abc') < set('abc')
Out[149]: False
since set('abc')
is not a proper subset of itself.
This operator is documented here.