adding snake case auto complete for https://github.com/ipython/ipython/issues/9420

IPython/core/completer.py

@@ -656,6 +656,15 b' class Completer(Configurable):'
             for word in lst:
                 if word[:n] == text and word != "__builtins__":
                     match_append(word)
+
+        snake_case_re = re.compile(r"[^_]+(_[^_]+)+?")
+        for lst in [self.namespace.keys(),
+                    self.global_namespace.keys()]:
+            shortened = {"_".join([sub[0] for sub in word.split('_')]) : word
+                         for word in lst if snake_case_re.fullmatch(word)}
+            for word in shortened.keys():
+                if word[:n] == text and word != "__builtins__":
+                    match_append(shortened[word])
         return [cast_unicode_py2(m) for m in matches]
 
     def attr_matches(self, text):

IPython/core/tests/test_completer.py

@@ -858,3 +858,11 b' def test_from_module_completer():'
     _, matches = ip.complete('B', 'from io import B', 16)
     nt.assert_in('BytesIO', matches)
     nt.assert_not_in('BaseException', matches)
+
+def test_snake_case_completion():
+    ip = get_ipython()
+    ip.user_ns['some_three'] = 3
+    ip.user_ns['some_four'] = 4
+    _, matches = ip.complete("s_", "print(s_f")
+    nt.assert_in('some_three', matches)
+    nt.assert_in('some_four', matches)
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