def to_timestamp(self, freq=None, how='<STR_LIT:start>', axis=<NUM_LIT:0>, copy=True):
new_data = self._data<EOL>if copy:<EOL><INDENT>new_data = new_data.copy()<EOL><DEDENT>axis = self._get_axis_number(axis)<EOL>if axis == <NUM_LIT:0>:<EOL><INDENT>new_data.set_axis(<NUM_LIT:1>, self.index.to_timestamp(freq=freq, how=how))<EOL><DEDENT>elif axis == <NUM_LIT:1>:<EOL><INDENT>new_data.set_axis(<NUM_LIT:0>, self.columns.to_timestamp(freq=freq, how=how))<EOL><DEDENT>else:  <EOL><INDENT>raise AssertionError('<STR_LIT>'.format(<EOL>ax=axis))<EOL><DEDENT>return self._constructor(new_data)<EOL>
Cast to DatetimeIndex of timestamps, at *beginning* of period.

Parameters
----------
freq : str, default frequency of PeriodIndex
    Desired frequency.
how : {'s', 'e', 'start', 'end'}
    Convention for converting period to timestamp; start of period
    vs. end.
axis : {0 or 'index', 1 or 'columns'}, default 0
    The axis to convert (the index by default).
copy : bool, default True
    If False then underlying input data is not copied.

Returns
-------
DataFrame with DatetimeIndex