REF: repr - allow block to override values that get formatted

pandas/core/internals.py

@@ -159,6 +159,10 @@ def internal_values(self, dtype=None):
         """
         return self.values
 
+    def formatting_values(self):
+        """Return the internal format used by the DataFrame/SeriesFormatter"""
+        return self.internal_values()
+
     def get_values(self, dtype=None):
         """
         return an internal format, currently just the ndarray

pandas/core/series.py

@@ -398,6 +398,12 @@ def _values(self):
         """ return the internal repr of this data """
         return self._data.internal_values()
 
+    def _formatting_values(self):
+        """Return the values that can be formatted (used by Series and
+        DataFrameFormatter)
+        """
+        return self._data._block.formatting_values()
+
     def get_values(self):
         """ same as values (but handles sparseness conversions); is a view """
         return self._data.get_values()

pandas/io/formats/format.py

@@ -237,7 +237,8 @@ def _get_formatted_index(self):
         return fmt_index, have_header
 
     def _get_formatted_values(self):
-        return format_array(self.tr_series._values, None,
+        values_to_format = self.tr_series._formatting_values()
+        return format_array(values_to_format, None,
                             float_format=self.float_format, na_rep=self.na_rep)
 
     def to_string(self):
@@ -694,7 +695,8 @@ def to_latex(self, column_format=None, longtable=False, encoding=None,
     def _format_col(self, i):
         frame = self.tr_frame
         formatter = self._get_formatter(i)
-        return format_array(frame.iloc[:, i]._values, formatter,
+        values_to_format = frame.iloc[:, i]._formatting_values()
+        return format_array(values_to_format, formatter,
                             float_format=self.float_format, na_rep=self.na_rep,
                             space=self.col_space, decimal=self.decimal)
 

pandas/tests/test_internals_external_block.py

@@ -0,0 +1,28 @@
+# -*- coding: utf-8 -*-
+# pylint: disable=W0102
+
+import numpy as np
+
+import pandas as pd
+from pandas.core.internals import Block, BlockManager
+
+
+class CustomBlock(Block):
+
+    def formatting_values(self):
+        return np.array(["Val: {}".format(i) for i in self.values])
+
+
+def test_custom_repr():
+    values = np.arange(3)
+
+    # series
+    block = CustomBlock(values, placement=slice(0, 3))
+    s = pd.Series(block, index=pd.RangeIndex(3), fastpath=True)
+    assert repr(s) == '0    Val: 0\n1    Val: 1\n2    Val: 2\ndtype: int64'
+
+    # dataframe
+    block = CustomBlock(values.reshape(1, -1), placement=slice(0, 1))
+    blk_mgr = BlockManager([block], [['col'], range(3)])
+    df = pd.DataFrame(blk_mgr)
+    assert repr(df) == '      col\n0  Val: 0\n1  Val: 1\n2  Val: 2'