dtype : str, numpy.dtype, or ExtensionDtype, optional
        Data type for the output Series. If not specified, this will be
        inferred from `data`.
        See the :ref:`user guide <basics.dtypes>` for more usages.
        If ``data`` is Series then is ignored.

>>> import pandas as pd
>>> ser = pd.Series([1,2,3])
>>> ser
0    1
1    2
2    3
dtype: int64
>>> pd.Series(ser, dtype=float)
0    1.0
1    2.0
2    3.0
dtype: float64