Truncate semantic pointer names to 1 KB

Fixes #244. 1 KB was chosen somewhat arbitrarily, but it seems long enough to capture the majority of use cases where someone might want to read the name, while being a cheap amount of memory relative to the resource requirements of the semantic pointer itself and how it will be used.

CHANGES.rst

@@ -34,6 +34,12 @@ Release History
   (`#239 <https://github.com/nengo/nengo_spa/issues/239>`__,
   `#240 <https://github.com/nengo/nengo_spa/pull/240>`__)
 
+**Fixed**
+
+- Fixed an issue where the names of iteratively generated semantic pointers
+  could grow exponentially in length, by truncating them at 1 KB.
+  (`#244 <https://github.com/nengo/nengo_spa/issues/244>`__,
+  `#246 <https://github.com/nengo/nengo_spa/pull/246>`__)
 
 
 1.0.1 (December 14, 2019)

nengo_spa/semantic_pointer.py

@@ -42,6 +42,8 @@ class SemanticPointer(Fixed):
         Name of the Semantic Pointer.
     """
 
+    MAX_NAME = 1024
+
     def __init__(self, data, vocab=None, algebra=None, name=None):
         super(SemanticPointer, self).__init__(
             TAnyVocab if vocab is None else TVocabulary(vocab)
@@ -54,6 +56,9 @@ def __init__(self, data, vocab=None, algebra=None, name=None):
         self.v.setflags(write=False)
 
         self.vocab = vocab
+
+        if name is not None and len(name) > self.MAX_NAME:
+            name = "%s..." % (name[: self.MAX_NAME - 3])
         self.name = name
 
     def _get_algebra(cls, vocab, algebra):

nengo_spa/tests/test_semantic_pointer.py

@@ -323,3 +323,9 @@ def test_name():
 
     assert (a + unnamed).name is None
     assert (a * unnamed).name is None
+
+    # check that names that blow up exponentially in length are truncated
+    for i in range(10):
+        a += a * b
+    assert len(a.name) == a.MAX_NAME
+    assert a.name.endswith("...")