Correction for BooleanLattice(n) for n=0 and n=1; some checks for input.

src/sage/combinat/posets/poset_examples.py

@@ -74,6 +74,12 @@ def __classcall__(cls, n = None):
         """
         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)
 
     @staticmethod
@@ -86,6 +92,16 @@ def BooleanLattice(n):
             sage: Posets.BooleanLattice(5)
             Finite lattice containing 32 elements
         """
+        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))
+        if n==0:
+            return LatticePoset( ([0], []) )
+        if n==1:
+            return LatticePoset( ([0,1], [[0,1]]) )
         return LatticePoset([[Integer(x|(1<<y)) for y in range(0,n) if x&(1<<y)==0] for
             x in range(0,2**n)])
 
@@ -120,6 +136,12 @@ def ChainPoset(n):
             sage: C.cover_relations()
             [[0, 1]]
         """
+        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 LatticePoset((range(n), [[x,x+1] for x in range(n-1)]))
 
     @staticmethod
@@ -152,6 +174,12 @@ def AntichainPoset(n):
             sage: C.cover_relations()
             []
         """
+        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 Poset((range(n), []))
 
     @staticmethod
@@ -209,6 +237,10 @@ def DiamondPoset(n, facade = None):
             sage: Posets.DiamondPoset(7)
             Finite lattice containing 7 elements
         """
+        try:
+            n = Integer(n)
+        except TypeError:
+            raise TypeError("Number of elements must be an integer, not {0}.".format(n))
         if n <= 2:
             raise ValueError("n must be an integer at least 3.")
         c = [[n-1] for x in range(n)]
@@ -370,9 +402,9 @@ def RandomPoset(n,p):
         try:
             n = Integer(n)
         except TypeError:
-            raise TypeError("number of elements must be an integer, not {0}".format(n))
+            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))
+            raise ValueError("Number of elements must be non-negative, not {0}.".format(n))
         try:
             p = float(p)
         except Exception: