pandas.Series.dt.normalize
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Series.dt.normalize(*args, **kwargs)[source]
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Return DatetimeIndex with times to midnight. Length is unaltered Returns: normalized : DatetimeIndex 
    © 2008–2012, AQR Capital Management, LLC, Lambda Foundry, Inc. and PyData Development Team
Licensed under the 3-clause BSD License.
    https://pandas.pydata.org/pandas-docs/version/0.20.3/generated/pandas.Series.dt.normalize.html