Do not shadow explicit magic completion.

If a binding has the same name than a magic, the magic should be
shadowed; unless the use is explicitly requesting a magic with a leading
percent sign.

Closes  #10754

IPython/core/completer.py

@@ -1222,6 +1222,8 b' class IPCompleter(Completer):'
         pre = self.magic_escape
         pre2 = pre+pre
         
+        explicit_magic = text.startswith(pre)
+
         # Completion logic:
         # - user gives %%: only do cell magics
         # - user gives %: do both line and cell magics
@@ -1229,11 +1231,23 b' class IPCompleter(Completer):'
         # In other words, line magics are skipped if the user gives %% explicitly
         #
         # We also exclude magics that match any currently visible names:
-        # https://github.com/ipython/ipython/issues/4877
+        # https://github.com/ipython/ipython/issues/4877, unless the user has
+        # typed a %:
+        # https://github.com/ipython/ipython/issues/10754
         bare_text = text.lstrip(pre)
         global_matches = self.global_matches(bare_text)
-        matches = lambda magic: magic.startswith(bare_text) \
-                                and magic not in global_matches
+        if not explicit_magic:
+            def matches(magic):
+                """
+                Filter magics, in particular remove magics that match
+                a name present in global namespace.
+                """
+                return ( magic.startswith(bare_text) and
+                         magic not in global_matches )
+        else:
+            def matches(magic):
+                return magic.startswith(bare_text)
+
         comp = [ pre2+m for m in cell_magics if matches(m)]
         if not text.startswith(pre2):
             comp += [ pre+m for m in line_magics if matches(m)]

IPython/core/tests/test_completer.py

@@ -589,6 +589,24 b' def test_magic_completion_shadowing():'
     text, matches = c.complete("mat")
     nt.assert_equal(matches, ["%matplotlib"])
 
+def test_magic_completion_shadowing_explicit():
+    """
+    If the user try to complete a shadowed magic, and explicit % start should
+    still return the completions.
+    """
+    ip = get_ipython()
+    c = ip.Completer
+
+    # Before importing matplotlib, %matplotlib magic should be the only option.
+    text, matches = c.complete("%mat")
+    nt.assert_equal(matches, ["%matplotlib"])
+
+    ip.run_cell("matplotlib = 1")
+
+    # After removing matplotlib from namespace, the magic should still be
+    # the only option.
+    text, matches = c.complete("%mat")
+    nt.assert_equal(matches, ["%matplotlib"])
 
 def test_magic_config():
     ip = get_ipython()