Merge branch 'issue_203' into 'stable'

Fix compatibility issues with Sympy 1.2.

Closes #203.

See merge request kwant/kwant!228

kwant/continuum/_common.py

@@ -190,6 +190,15 @@ def sympify(expr, locals=None):
             converter[list] = stored_value
         else:
             del converter[list]
+
+    # We assume that all present functions, like "sin", "cos", will be
+    # provided by user during the final evaluation through "params".
+    # Therefore we make sure they are define as AppliedUndef, not built-in
+    # sympy types.
+    subs = {r: sympy.Symbol(str(r.func))(*r.args)
+            for r in hamiltonian.atoms(sympy.Function)}
+
+    hamiltonian = hamiltonian.subs(subs)
     return hamiltonian
 
 

kwant/continuum/discretizer.py

@@ -457,6 +457,11 @@ def _discretize_expression(expression, coords):
 
 class _NumericPrinter(LambdaPrinter):
 
+    def __init__(self):
+        LambdaPrinter.__init__(self)
+        self.known_functions = {}
+        self.known_constants = {'pi': 'pi', 'Pi': 'pi'}
+
     def _print_ImaginaryUnit(self, expr):
         # prevent sympy from printing 'I' for imaginary unit
         return "1j"

kwant/continuum/tests/test_common.py

@@ -97,9 +97,9 @@ res_mat = sympy.Matrix([[x**3*A + x**2*A + x**2*B, x**3*A + x**2*A + x**2*B + x*
 
 
 def test_make_commutative():
-    assert make_commutative(expr1, x) == make_commutative(expr1, non_x)
-    assert make_commutative(expr1, x) == x**3*A + x**2*A + x**2*B
-    assert make_commutative(matr, x) == res_mat
+    assert make_commutative(expr1, x).expand() == (make_commutative(expr1, non_x)).expand()
+    assert make_commutative(expr1, x).expand() == (x**3*A + x**2*A + x**2*B).expand()
+    assert make_commutative(matr, x).expand() == (res_mat).expand()
 
 
 expr2 = non_x*A*non_x + x**2 * A*2 * x + B*non_x/2 + non_x*B/2 + x + A + non_x + x/A