code: def _get_const_index(exog):
      """
      Returns a boolean array of non-constant column indices in exog and
      an scalar array of where the constant is or None
      """
      effects_idx = exog.var(0) != 0
      if np.any(~effects_idx):
          const_idx = np.where(~effects_idx)[0]
      else:
          const_idx = None
      return effects_idx, const_idx
  
imports: from statsmodels.compat.python import lzip
  import numpy
  from scipy.stats import norm
  from statsmodels.tools.decorators import cache_readonly
label_desc: Use image node_id 3 for calling a global function with example usage: _get_const_index(exog) and returns: effects_idx,  const_idx