def __iter__(self):
r"""
Iterator over representatives of the isomorphism classes of
posets with finitely many vertices.
.. warning:: this feature may become deprecated, since it does
of course not iterate through all posets.
EXAMPLES::
sage: P = Posets()
sage: it = iter(P)
sage: for _ in range(10): print next(it);
Finite poset containing 0 elements
Finite poset containing 1 elements
Finite poset containing 2 elements
Finite poset containing 2 elements
Finite poset containing 3 elements
Finite poset containing 3 elements
Finite poset containing 3 elements
Finite poset containing 3 elements
Finite poset containing 3 elements
Finite poset containing 4 elements
"""
from sage.combinat.posets.posets import FinitePosets_n
n = 0
while True:
for P in FinitePosets_n(n):
yield P
n += 1
def __classcall__(cls, n = None):
r"""
Return either the category of all posets, or the finite
enumerated set of all finite posets on ``n`` elements up to an
isomorphism.
EXAMPLES::
sage: Posets()
Category of posets
sage: Posets(4)
Posets containing 4 vertices
"""
if n is None:
return sage.categories.posets.Posets()
return FinitePosets_n(n)
def __classcall__(cls, n=None):
r"""
Return either the category of all posets, or the finite
enumerated set of all finite posets on ``n`` elements up to an
isomorphism.
EXAMPLES::
sage: Posets()
Category of posets
sage: Posets(4)
Posets containing 4 vertices
"""
if n is None:
return sage.categories.posets.Posets()
try:
n = Integer(n)
except TypeError:
raise TypeError(
"number of elements must be an integer, not {0}".format(n))
if n < 0:
raise ValueError(
"number of elements must be non-negative, not {0}".format(n))
return FinitePosets_n(n)