elide long containers in pretty

limits sequence length to 1k items

avoids performance issues with pretty-printing large containers

IPython/lib/pretty.py

@@ -122,6 +122,7 b' else:'
 __all__ = ['pretty', 'pprint', 'PrettyPrinter', 'RepresentationPrinter',
     'for_type', 'for_type_by_name']
 
+SEQ_LENGTH_LIMIT = 1000
 
 _re_pattern_type = type(re.compile(''))
 
@@ -599,6 +600,12 b' def _seq_pprinter_factory(start, end, basetype):'
         step = len(start)
         p.begin_group(step, start)
         for idx, x in enumerate(obj):
+            if idx >= SEQ_LENGTH_LIMIT:
+                p.text(',')
+                p.breakable()
+                p.text('...')
+                p.end_group(step, end)
+                return
             if idx:
                 p.text(',')
                 p.breakable()
@@ -636,6 +643,12 b' def _set_pprinter_factory(start, end, basetype):'
                 # Sometimes the items don't sort.
                 pass
             for idx, x in enumerate(items):
+                if idx >= SEQ_LENGTH_LIMIT:
+                    p.text(',')
+                    p.breakable()
+                    p.text('...')
+                    p.end_group(step, end)
+                    return
                 if idx:
                     p.text(',')
                     p.breakable()
@@ -665,6 +678,12 b' def _dict_pprinter_factory(start, end, basetype=None):'
             # Sometimes the keys don't sort.
             pass
         for idx, key in enumerate(keys):
+            if idx >= SEQ_LENGTH_LIMIT:
+                p.text(',')
+                p.breakable()
+                p.text('...')
+                p.end_group(1, end)
+                return
             if idx:
                 p.text(',')
                 p.breakable()

IPython/lib/tests/test_pretty.py

@@ -196,4 +196,29 b' def test_super_repr():'
     sb = SB()
     output = pretty.pretty(super(SA, sb))
     nt.assert_in("SA", output)
-    
  No newline at end of file
+
+
+def test_long_list():
+    lis = list(range(10000))
+    p = pretty.pretty(lis)
+    last2 = p.rsplit('\n', 2)[-2:]
+    nt.assert_equal(last2, [' 999,', ' ...]'])
+
+def test_long_set():
+    s = set(range(10000))
+    p = pretty.pretty(s)
+    last2 = p.rsplit('\n', 2)[-2:]
+    nt.assert_equal(last2, [' 999,', ' ...}'])
+
+def test_long_tuple():
+    tup = tuple(range(10000))
+    p = pretty.pretty(tup)
+    last2 = p.rsplit('\n', 2)[-2:]
+    nt.assert_equal(last2, [' 999,', ' ...)'])
+
+def test_long_dict():
+    d = { n:n for n in range(10000) }
+    p = pretty.pretty(d)
+    last2 = p.rsplit('\n', 2)[-2:]
+    nt.assert_equal(last2, [' 999: 999,', ' ...}'])
+