'Efficiently update data source columns with new append-only data.
In cases where it is necessary to update data columns in, this method
can efficiently send only the new data, instead of requiring the
entire data set to be re-sent.
Args:
new_data (dict[str, seq]) : a mapping of column names to sequences of
new data to append to each column.
All columns of the data source must be present in ``new_data``,
with identical-length append data.
rollover (int, optional) : A maximum column size, above which data
from the start of the column begins to be discarded. If None,
then columns will continue to grow unbounded (default: None)
Returns:
None
Raises:
ValueError
Example:
.. code-block:: python
source = ColumnDataSource(data=dict(foo=[], bar=[]))
# has new, identical-length updates for all columns in source
new_data = {
\'foo\' : [10, 20],
\'bar\' : [100, 200],
source.stream(new_data)'

def stream(self, new_data, rollover=None):

    self._stream(new_data, rollover)
