17399: handle series in ex.coefficients()

src/sage/symbolic/expression.pyx

@@ -5173,6 +5173,8 @@ cdef class Expression(CommutativeRingElement):
             [[2*a^2 + 1, 0], [-2*sqrt(2)*a + 1, 1], [1, 2]]
             sage: p.coefficients(x, sparse=False)
             [2*a^2 + 1, -2*sqrt(2)*a + 1, 1]
+            
+        TESTS:
 
         The behaviour is undefined with noninteger or negative exponents::
 
@@ -5190,17 +5192,34 @@ cdef class Expression(CommutativeRingElement):
             doctest:...: DeprecationWarning: coeffs is deprecated. Please use coefficients instead.
             See http://trac.sagemath.org/17438 for details.
             [[1, 1]]
+        
+        Series coefficients are now handled correctly (:trac:`17399`)::
+        
+            sage: s=(1/(1-x)).series(x,6); s
+            1 + 1*x + 1*x^2 + 1*x^3 + 1*x^4 + 1*x^5 + Order(x^6)
+            sage: s.coefficients()
+            [[1, 0], [1, 1], [1, 2], [1, 3], [1, 4], [1, 5]]
+            sage: s.coefficients(x, sparse=False)
+            [1, 1, 1, 1, 1, 1]
+            sage: x,y = var("x,y")
+            sage: s=(1/(1-y*x-x)).series(x,3); s
+            1 + (y + 1)*x + ((y + 1)^2)*x^2 + Order(x^3)
+            sage: s.coefficients(x, sparse=False)
+            [1, y + 1, (y + 1)^2]
         """
-        f = self._maxima_()
-        maxima = f.parent()
-        maxima._eval_line('load(coeflist)')
         if x is None:
             x = self.default_variable()
-        x = self.parent().var(repr(x))
-        G = f.coeffs(x)
-        from sage.calculus.calculus import symbolic_expression_from_maxima_string
-        S = symbolic_expression_from_maxima_string(repr(G))
-        l = S[1:]
+        if is_a_series(self._gobj):
+            l = [[self.coefficient(x, d), d] for d in xrange(self.degree(x))]
+        else:
+            f = self._maxima_()
+            maxima = f.parent()
+            maxima._eval_line('load(coeflist)')
+            G = f.coeffs(x)
+            from sage.calculus.calculus import symbolic_expression_from_maxima_string
+            S = symbolic_expression_from_maxima_string(repr(G))
+            l = S[1:]
+
         if sparse is True:
             return l
         else:
@@ -5237,16 +5256,17 @@ cdef class Expression(CommutativeRingElement):
             (x, y, a)
             sage: (x^5).list()
             [0, 0, 0, 0, 0, 1]
-            sage: p = x^3 - (x-3)*(x^2+x) + 1
-            sage: p.list()
-            [1, 3, 2]
             sage: p = x - x^3 + 5/7*x^5
             sage: p.list()
             [0, 1, 0, -1, 0, 5/7]
             sage: p = expand((x-a*sqrt(2))^2 + x + 1); p
             -2*sqrt(2)*a*x + 2*a^2 + x^2 + x + 1
             sage: p.list(a)
             [x^2 + x + 1, -2*sqrt(2)*x, 2]
+            sage: s=(1/(1-x)).series(x,6); s
+            1 + 1*x + 1*x^2 + 1*x^3 + 1*x^4 + 1*x^5 + Order(x^6)
+            sage: s.list()
+            [1, 1, 1, 1, 1, 1]
         """
         return self.coefficients(x=x, sparse=False)