Support Bytes dict completions, and test it.

Closes  #8647

IPython/core/completer.py

@@ -622,8 +622,27 b' def get__all__entries(obj):'
     return [cast_unicode_py2(w) for w in words if isinstance(w, str)]
 
 
-def match_dict_keys(keys, prefix, delims):
-    """Used by dict_key_matches, matching the prefix to a list of keys"""
+def match_dict_keys(keys: List[str], prefix: str, delims: str):
+    """Used by dict_key_matches, matching the prefix to a list of keys
+
+    Parameters
+    ==========
+        keys:
+            list of keys in dictionary currently being completed.
+        prefix:
+            Part of the text already typed by the user. e.g. `mydict[b'fo`
+        delims:
+            String of delimiters to consider when finding the current key.
+
+    Returns
+    =======
+
+    A tuple of three elements: ``quote``, ``token_start``, ``matched``, with
+    ``quote`` being the quote that need to be used to close current string.
+    ``token_start`` the position where the replacement should start occurring,
+    ``matches`` a list of replacement/completion
+
+    """
     if not prefix:
         return None, 0, [repr(k) for k in keys
                       if isinstance(k, (str, bytes))]
@@ -639,7 +658,6 b' def match_dict_keys(keys, prefix, delims):'
     token_start = token_match.start()
     token_prefix = token_match.group()
 
-    # TODO: support bytes in Py3k
     matched = []
     for key in keys:
         try:
@@ -652,7 +670,7 b' def match_dict_keys(keys, prefix, delims):'
         # reformat remainder of key to begin with prefix
         rem = key[len(prefix_str):]
         # force repr wrapped in '
-        rem_repr = repr(rem + '"')
+        rem_repr = repr(rem + '"') if isinstance(rem, str) else repr(rem + b'"')
         if rem_repr.startswith('u') and prefix[0] not in 'uU':
             # Found key is unicode, but prefix is Py2 string.
             # Therefore attempt to interpret key as string.

IPython/core/tests/test_completer.py

@@ -20,7 +20,7 b' from IPython.utils.tempdir import TemporaryDirectory, TemporaryWorkingDirectory'
 from IPython.utils.generics import complete_object
 from IPython.testing import decorators as dec
 
-from IPython.core.completer import Completion, provisionalcompleter
+from IPython.core.completer import Completion, provisionalcompleter, match_dict_keys
 from nose.tools import assert_in, assert_not_in
 
 #-----------------------------------------------------------------------------
@@ -526,7 +526,28 b' def test_magic_completion_order():'
 
     # Order of user variable and line and cell magics with same name:
     text, matches = c.complete('timeit')
-    nt.assert_equal(matches, ["timeit", "%timeit","%%timeit"])
+    nt.assert_equal(matches, ["timeit", "%timeit", "%%timeit"])
+
+def test_match_dict_keys():
+    """
+    Test that match_dict_keys works on a couple of use case does return what
+    expected, and does not crash
+    """
+    delims = ' \t\n`!@#$^&*()=+[{]}\\|;:\'",<>?'
+
+
+    keys = ['foo', b'far']
+    assert match_dict_keys(keys, "b'", delims=delims)  == ("'", 2 ,['far'])
+    assert match_dict_keys(keys, "b'f", delims=delims) == ("'", 2 ,['far'])
+    assert match_dict_keys(keys, 'b"', delims=delims)  == ('"', 2 ,['far'])
+    assert match_dict_keys(keys, 'b"f', delims=delims) == ('"', 2 ,['far'])
+
+    assert match_dict_keys(keys, "'", delims=delims)  == ("'", 1 ,['foo'])
+    assert match_dict_keys(keys, "'f", delims=delims) == ("'", 1 ,['foo'])
+    assert match_dict_keys(keys, '"', delims=delims)  == ('"', 1 ,['foo'])
+    assert match_dict_keys(keys, '"f', delims=delims) == ('"', 1 ,['foo'])
+    
+    match_dict_keys
 
 
 def test_dict_key_completion_string():