Fix AlignedSegment's pack_tags()'s exceptions

There is no `array.typecode` class attribute, so the `array.array`
arm produced an AttributeError instead of the intended ValueError.
Perhaps `value.typecode` was intended; but this error only arises
when a `value_type` has been specified, so the array's typecode
has no influence on `typecode` anyway. So we simplify the message.

Also add a similar check in the scalar arm of this if-else to avoid
an invalid `typecode` here being reported as a raw KeyError.

Fixes #1233. Closes #1235 -- hat tip @marcus1487 for issue analysis.

[TODO] All this code is confusing and should be rewritten using
HTSlib's more recent aux field manipulation APIs.

pysam/libcalignedsegment.pyx

@@ -382,7 +382,7 @@ cdef inline pack_tags(tags):
                     raise ValueError("unsupported type code '{}'".format(value.typecode))
 
             if typecode not in DATATYPE2FORMAT:
-                raise ValueError("invalid value type '{}' ({})".format(chr(typecode), array.typecode))
+                raise ValueError("invalid value type '{}'".format(chr(typecode)))
 
             # use array.tostring() to retrieve byte representation and
             # save as bytes
@@ -407,8 +407,10 @@ cdef inline pack_tags(tags):
 
             if typecode == b'Z' or typecode == b'H':
                 datafmt = "2sB%is" % (len(value)+1)
-            else:
+            elif typecode in DATATYPE2FORMAT:
                 datafmt = "2sB%s" % DATATYPE2FORMAT[typecode][0]
+            else:
+                raise ValueError("invalid value type '{}'".format(chr(typecode)))
 
             args.extend([pytag[:2],
                          typecode,

tests/AlignedSegment_test.py

@@ -1624,6 +1624,18 @@ def test_set_tag_with_automated_type_detection(self):
             alt_value_type="I",
         )
 
+    def test_set_tag_invalid_value_type(self):
+        with self.assertRaises(ValueError):
+            self.check_tag("TT", "abc", value_type="#")
+
+    def test_set_array_tag_invalid_value_type(self):
+        with self.assertRaises(ValueError):
+            self.check_tag("TT", array.array('I', range(4)), value_type='#')
+
+    def test_set_array_tag_invalid_typecode(self):
+        with self.assertRaises(ValueError):
+            self.check_tag("TT", array.array('L', range(4)), value_type=None)
+
 
 class TestSetTagsGetTag(TestSetTagGetTag):
     def check_tag(self, tag, value, value_type, alt_value_type=None):