sagemathgh-39693: Added the rank method under ModulesWithBasis.ParentMethod.
    
sagemath#34445
It is based on the understanding that dimension is equal rank under the
context, assuming rank defined for infinite dimensional space.

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URL: sagemath#39693
Reported by: Henry Wu
Reviewer(s): Henry Wu, Travis Scrimshaw

Author: Release Manager

src/sage/categories/modules_with_basis.py

@@ -1309,6 +1309,30 @@ def dimension(self):
                 from sage.rings.integer_ring import ZZ
                 return ZZ(len(self.basis()))
 
+        def rank(self):
+            """
+            Return the rank of ``self``.
+
+            Since there is a (distinguished) basis, the rank of ``self``
+            is equal to the cardinality of the basis (which equals
+            the :meth:`dimension` of ``self``).
+
+            EXAMPLES::
+
+                sage: A.<x,y> = algebras.DifferentialWeyl(QQ)                           # needs sage.modules
+                sage: A.rank()                                                          # needs sage.modules
+                +Infinity
+
+                sage: R.<x,y> = QQ[]
+                sage: R.rank()
+                +Infinity
+
+                sage: F = CombinatorialFreeModule(QQ, ['a','b','c'])
+                sage: F.rank()
+                3
+            """
+            return self.dimension()
+
         def _from_dict(self, d, coerce=True, remove_zeros=True):
             """
             Construct an element of ``self`` from the dictionary ``d``.