ENH: set display.max_seq_items default != None

Author: y-p

doc/source/release.rst

@@ -388,6 +388,8 @@ API Changes
     dates are given (:issue:`5242`)
   - ``Timestamp`` now supports ``now/today/utcnow`` class methods
     (:issue:`5339`)
+  - default for `display.max_seq_len` is now 100 rather then `None`. This activates
+    truncated display ("...") of long sequences in various places. (:issue:`3391`)
   - **All** division with ``NDFrame`` - likes is now truedivision, regardless
     of the future import. You can use ``//`` and ``floordiv`` to do integer
     division.

doc/source/v0.13.0.txt

@@ -147,6 +147,8 @@ These were announced changes in 0.12 or prior that are taking effect as of 0.13.
 - Remove deprecated ``_verbose_info`` (:issue:`3215`)
 - Remove deprecated ``read_clipboard/to_clipboard/ExcelFile/ExcelWriter`` from ``pandas.io.parsers`` (:issue:`3717`)
 - default for ``tupleize_cols`` is now ``False`` for both ``to_csv`` and ``read_csv``. Fair warning in 0.12 (:issue:`3604`)
+- default for `display.max_seq_len` is now 100 rather then `None`. This activates
+  truncated display ("...") of long sequences in various places. (:issue:`3391`)
 
 Deprecations
 ~~~~~~~~~~~~

pandas/core/config_init.py

@@ -246,7 +246,7 @@ def mpl_style_cb(key):
                        validator=is_text)
     cf.register_option('expand_frame_repr', True, pc_expand_repr_doc)
     cf.register_option('chop_threshold', None, pc_chop_threshold_doc)
-    cf.register_option('max_seq_items', None, pc_max_seq_items)
+    cf.register_option('max_seq_items', 100, pc_max_seq_items)
     cf.register_option('mpl_style', None, pc_mpl_style_doc,
                        validator=is_one_of_factory([None, False, 'default']),
                        cb=mpl_style_cb)

pandas/tests/test_format.py

@@ -141,9 +141,8 @@ def test_repr_chop_threshold(self):
     def test_repr_obeys_max_seq_limit(self):
         import pandas.core.common as com
 
-        #unlimited
-        reset_option("display.max_seq_items")
-        self.assertTrue(len(com.pprint_thing(lrange(1000)))> 2000)
+        with option_context("display.max_seq_items",2000):
+            self.assertTrue(len(com.pprint_thing(lrange(1000))) > 1000)
 
         with option_context("display.max_seq_items",5):
             self.assertTrue(len(com.pprint_thing(lrange(1000)))< 100)