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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def select_time(da, **indexer):
 """Select entries according to a time period. Parameters da : xarray.DataArray Input data. **indexer : {dim: indexer, }, optional Time attribute and values over which to subset the array. For example, use season='DJF' to select winter values, month=1 to select January, or month=[6,7,8] to select summer months. If not indexer is given, all values are considered. Returns ------- xr.DataArray Selected input values. """

    if not indexer:
        selected = da
    else:
        key, val = indexer.popitem()
        time_att = getattr(da.time.dt, key)
        selected = da.sel(time=time_att.isin(val)).dropna(dim='time')

    return selected