code: def annual_volatility(
      returns, period=DAILY, alpha=2.0, annualization=None
  ):
      """
      Determines the annual volatility of a strategy.
  
      Parameters
      ----------
      returns : pd.Series or np.ndarray
          Periodic returns of the strategy, noncumulative.
          - See full explanation in :func:`~empyrical.stats.cum_returns`.
      period : str, optional
          Defines the periodicity of the 'returns' data for purposes of
          annualizing. Value ignored if `annualization` parameter is specified.
          Defaults are:
              'monthly':12
              'weekly': 52
              'daily': 252
      alpha : float, optional
          Scaling relation (Levy stability exponent).
      annualization : int, optional
          Used to suppress default values available in `period` to convert
          returns into annual returns. Value should be the annual frequency of
          `returns`.
  
      Returns
      -------
      float
          Annual volatility.
      """
  
      if len(returns) < 2:
          return np.nan
  
      ann_factor = annualization_factor(period, annualization)
  
      volatility = nanstd(returns, ddof=1) * (
          ann_factor ** (1.0 / alpha)
      )
  
      return volatility
  
imports: from __future__ import division
  from functools import wraps
  import pandas
  import numpy
  from scipy import stats
  from six import iteritems
  from empyrical.utils import nanmean, nanstd, nanmin
label_desc: Use image node_id 10 for calling a global function with example usage: annual_volatility(returns, period, alpha, annualization) and returns: volatility, np