clear out the contents of but keep length of In[]

IPython/core/tests/test_magic.py

@@ -211,7 +211,7 def test_clear():
     nt.assert_true('parrot' in [_ip.user_ns[x] for x in '_i','_ii','_iii'])
     _ip.magic('%clear in')
     nt.assert_false('parrot' in [_ip.user_ns[x] for x in '_i','_ii','_iii'])
-    nt.assert_true(len(_ip.user_ns['In']) == 0)
+    nt.assert_true(len(set(_ip.user_ns['In'])) == 1)
 
     # test '%clear dhist'
     _ip.run_cell("tmp = [d for d in _dh]") # copy before clearing
@@ -222,6 +222,11 def test_clear():
     nt.assert_true(len(_ip.user_ns['_dh']) == 0)
     _ip.run_cell("_dh = [d for d in tmp]") #restore
 
+    # test that In length is preserved for %macro
+    _ip.run_cell("print 'foo'")
+    _ip.run_cell("clear in")
+    nt.assert_true(len(_ip.user_ns['In']) == _ip.displayhook.prompt_count+1)
+
 def test_time():
     _ip.magic('time None')
 

IPython/extensions/clearcmd.py

@@ -45,8 +45,10 def clear_f(self,arg):
                 key = '_i'+repr(n)
                 user_ns.pop(key,None)
             user_ns.update(dict(_i=u'',_ii=u'',_iii=u''))
-            del self.history_manager.input_hist_parsed[:]
-            del self.history_manager.input_hist_raw[:]
+            # don't delete these, as %save and %macro depending on the length
+            # of these lists to be preserved
+            self.history_manager.input_hist_parsed[:] = [''] * pc
+            self.history_manager.input_hist_raw[:] = [''] * pc
 
         elif target == 'array':
             # Support cleaning up numpy arrays