Support adding/removing address checksums

Two new methods in Address class:

 - add_checksum: appends a valid checksum to
   the Address object.

 - remove_checksum: slices off the checksum from
   an Address object.

iota/types.py

@@ -870,6 +870,28 @@ def _generate_checksum(self):
 
         return AddressChecksum.from_trits(checksum_trits[-checksum_length:])
 
+    def add_checksum(self):
+        # type: () -> None
+        """
+        Add checksum to :py:class:`Address` object.
+        """
+        if self.is_checksum_valid():
+            # Address already has a valid checksum.
+            return
+
+        # Fill checksum attribute
+        self.checksum = self._generate_checksum()
+
+        # Add generated checksum to internal buffer.
+        self._trytes = self._trytes + self.checksum._trytes
+
+    def remove_checksum(self):
+        # type: () -> None
+        """
+        Remove checksum from :py:class:`Address` object.
+        """
+        self.checksum = None
+        self._trytes = self._trytes[:self.LEN]
 
 class AddressChecksum(TryteString):
     """

test/types_test.py

@@ -1049,6 +1049,39 @@ def test_with_checksum_attributes(self):
     self.assertEqual(checked.key_index, 42)
     self.assertEqual(checked.balance, 86)
 
+  def test_add_checksum(self):
+    """
+    Checksum is added to an address without it.
+    """
+    addy = Address(
+      trytes =
+        b'ZKIUDZXQYQAWSHPKSAATJXPAQZPGYCDCQDRSMWWCGQJNI'
+        b'PCOORMDRNREDUDKBMUYENYTFVUNEWDBAKXMV'
+    )
+
+    addy.add_checksum()
+
+    self.assertTrue(addy.is_checksum_valid())
+    self.assertTrue(len(addy) == Address.LEN + AddressChecksum.LEN)
+
+  def test_remove_checksum(self):
+    """
+    Checksum is removed from an address.
+    """
+    addy = Address(
+      trytes =
+        b'ZKIUDZXQYQAWSHPKSAATJXPAQZPGYCDCQDRSMWWCGQJNI'
+        b'PCOORMDRNREDUDKBMUYENYTFVUNEWDBAKXMVJJJGBARPB'
+    )
+
+    self.assertTrue(addy.is_checksum_valid())
+    self.assertTrue(len(addy) == Address.LEN + AddressChecksum.LEN)
+
+    addy.remove_checksum()
+
+    self.assertFalse(addy.is_checksum_valid())
+    self.assertTrue(len(addy) == Address.LEN)
+
 
 # noinspection SpellCheckingInspection
 class AddressChecksumTestCase(TestCase):