Fix the behavior of Dop with no arguments

This fixes the `TestDop.test_empty_dop` test.

Author: eric-wieser

galgebra/mv.py

@@ -1964,16 +1964,20 @@ def __init__(self, *args, **kwargs):
         self.title = None
 
         if len(args) == 2:
-            if len(args[0]) != len(args[1]):
+            coefs, pdiffs = args
+            if len(coefs) != len(pdiffs):
                 raise ValueError('In Dop.__init__ coefficent list and Pdop list must be same length.')
-            self.terms = tuple(zip(args[0], args[1]))
+            self.terms = tuple(zip(coefs, pdiffs))
         elif len(args) == 1:
-            if isinstance(args[0][0][0], Mv):  # Mv expansion [(Mv, Pdop)]
-                self.terms = tuple(args[0])
-            elif isinstance(args[0][0][0], Sdop):  # Sdop expansion [(Sdop, Mv)]
+            arg, = args
+            if len(arg) == 0:
+                self.terms = ()
+            elif isinstance(arg[0][0], Mv):  # Mv expansion [(Mv, Pdop)]
+                self.terms = tuple(arg)
+            elif isinstance(arg[0][0], Sdop):  # Sdop expansion [(Sdop, Mv)]
                 coefs = []
                 pdiffs = []
-                for (sdop, mv) in args[0]:
+                for (sdop, mv) in arg:
                     for (coef, pdiff) in sdop.terms:
                         if pdiff in pdiffs:
                             index = pdiffs.index(pdiff)
@@ -2037,23 +2041,18 @@ def Add(dop1, dop2):
             if dop1.cmpflg != dop2.cmpflg:
                 raise ValueError('In Dop.Add complement flags have different values: %s vs. %s' % (dop1.cmpflg, dop2.cmpflg))
 
-            coefs1, pdiffs1 = list(zip(*dop1.terms))
-            coefs2, pdiffs2 = list(zip(*dop2.terms))
-
-            pdiffs1 = list(pdiffs1)
-            pdiffs2 = list(pdiffs2)
+            pdiffs1 = [pdiff for _, pdiff in dop1.terms]
+            pdiffs2 = [pdiff for _, pdiff in dop2.terms]
 
             pdiffs = pdiffs1 + [x for x in pdiffs2 if x not in pdiffs1]
             coefs = len(pdiffs) * [S(0)]
 
-            for pdiff in pdiffs1:
+            for coef, pdiff in dop1.terms:
                 index = pdiffs.index(pdiff)
-                coef = coefs1[pdiffs1.index(pdiff)]
                 coefs[index] += coef
 
-            for pdiff in pdiffs2:
+            for coef, pdiff in dop2.terms:
                 index = pdiffs.index(pdiff)
-                coef = coefs2[pdiffs2.index(pdiff)]
                 coefs[index] += coef
 
             return Dop(coefs, pdiffs, cmpflg=dop1.cmpflg, ga=dop1.Ga)

test/test_differential_ops.py

@@ -32,7 +32,6 @@ def test_associativity_and_distributivity(self):
         assert v ^ (ga.rgrad ^ ex) == (v ^ ga.rgrad) ^ ex != 0
         assert v ^ (ga.rgrad ^ 20) == (v ^ ga.rgrad) ^ 20 != 0
 
-    @pytest.mark.xfail(raises=IndexError)
     def test_empty_dop(self):
         """ Test that dop with zero terms is equivalent to multiplying by zero """
         coords = x, y, z = symbols('x y z', real=True)