Merge pull request #180 from daico007/element.py

Make `Element` immutable

topology/core/element.py

@@ -2,34 +2,19 @@
 from re import sub
 
 import numpy as np
+from collections import namedtuple
 import unyt as u
 
 from topology.exceptions import TopologyError
 
-
-class Element(object):
+class Element(namedtuple('Element', 'atomic_number, name, symbol, mass')):
     """An element."""
-    def __init__(self, atomic_number=None, name=None, symbol=None, mass=None):
-        self._atomic_number = atomic_number
-        self._name = name
-        self._symbol = symbol
-        self._mass = mass
-
-    @property
-    def atomic_number(self):
-        return self._atomic_number
-
-    @property
-    def name(self):
-        return self._name
-
-    @property
-    def symbol(self):
-        return self._symbol
-
-    @property
-    def mass(self):
-        return self._mass
+
+    def __str__(self):
+        return 'Element: {}, symbol: {}, atomic number: {}, mass: {}'.format(
+                                                                      self.name, self.symbol,
+                                                                      self.atomic_number,
+                                                                      self.mass)
 
 
 def element_by_symbol(symbol):

topology/tests/base_test.py

@@ -4,7 +4,7 @@
 
 from topology.core.box import Box
 from topology.core.topology import Topology
-from topology.core.element import Element
+from topology.core.element import Hydrogen
 from topology.core.site import Site
 from topology.core.atom_type import AtomType
 
@@ -43,11 +43,11 @@ def topology_site(self):
         def _topology(sites=1):
             top = Topology()
             top.box = Box(lengths=[1, 1, 1])
-            H = Element(name='H', symbol='H', mass=1)
+            H = Hydrogen
             site1 = Site(name='site1',
                          element=H,
                          atom_type=AtomType(name="at1",
-                                            mass=H.mass)
+                                            mass=H.mass),
                          )
             for i in range(sites):
                 top.add_site(site1)