skip encoding for strings with len > 4

rcsb/mmtf#37

simplemmtf.py

@@ -437,6 +437,22 @@ def _PackedIntBufStrategy(nbytes=1, dectype='i4'):
 ########## MEDIUM LEVEL ARRAY ENCODE/DECODE API #################
 
 
+def check_encodable(arr, codec, param=0):
+    '''Check if an array is encodable with the requested strategy.
+
+    Example of type 5 "fixed-length string array" with string length 4:
+
+        >>> check_encodable(["ABCD"], 5, 4)
+        True
+        >>> check_encodable(["ABCDE"], 5, 4)
+        False
+    '''
+    if codec == 5:
+        return all(len(s) <= param for s in arr)
+
+    return True
+
+
 def encode_array(arr, codec, param=0):
     strategy = strategies[codec](param)
 
@@ -757,7 +773,7 @@ def set(self, key, value, codec=-1, param=0):
         if codec == -1:
             codec, param = encodingrules.get(key, (0, 0))
 
-        if codec != 0:
+        if codec != 0 and check_encodable(value, codec, param):
             value = encode_array(value, codec, param)
 
         self._data[mmtfstr(key)] = value

test.py

@@ -110,11 +110,34 @@ def test_encode_recode():
             raise UserWarning(key)
 
 
+def test_encodable():
+    atoms = [{
+        u'atomName': u'N',
+        u'chainId': u'A',
+        u'coords': (12.284, 42.763, 10.037),
+        u'element': u'N',
+        u'groupName': u'MET',
+    }]
+
+    # len('A') <= 4: encodable -> binary
+    d = simplemmtf.from_atoms(atoms)
+    assert d.get(u'chainIdList') == ['A']
+    assert isinstance(d._data[u'chainIdList'], bytes)
+
+    atoms[0][u'chainId'] = u'ABCDE'
+
+    # len('ABCDE') > 4: not encodable -> array
+    d = simplemmtf.from_atoms(atoms)
+    assert d.get(u'chainIdList') == ['ABCDE']
+    assert isinstance(d._data[u'chainIdList'], list)
+
+
 def test():
     for fn in sys.argv[1:]:
         test_file(fn)
 
     test_encode_recode()
+    test_encodable()
 
 
 if __name__ == '__main__':