class_docstr: Computes the dispersion relative to the mean value, ignoring `NaN`.
  
  Examples:
      >>> std = Std()
      >>> round(std([1, 2, 3, 4, 5, None]), 3)
      1.414
code: def get_function(self, agg_type=Library.PANDAS):
      if agg_type in [Library.DASK, Library.SPARK]:
          return "std"
  
      return np.std
  
imports: import numpy
  from woodwork.column_schema import ColumnSchema
  from featuretools.primitives.base.aggregation_primitive_base import AggregationPrimitive
  from featuretools.utils.gen_utils import Library
label_desc: Use image node_id 1 for calling the Std obj's underlying member method code with example usage: obj.get_function(agg_type) and returns: np, str