code: def isin(X,Y):
      
      if len(Y) > 0:
          T = Y.copy()
          T.sort()
          D = T.searchsorted(X)
          T = np.append(T,np.array([0]))
          W = (T[D] == X)
          if isinstance(W,bool):
              return np.zeros((len(X),),bool)
          else:
              return (T[D] == X)
      else:
          return np.zeros((len(X),),bool)
docs: Indices of elements in a numpy array that appear in another.
  
      Fast routine for determining indices of elements in numpy array `X` that 
      appear in numpy array `Y`, returning a boolean array `Z` such that::
  
              Z[i] = X[i] in Y
  
      **Parameters**
  
              **X** :  numpy array
  
                      Numpy array to comapare to numpy array `Y`.  For each 
                      element of `X`, ask if it is in `Y`.
  
              **Y** :  numpy array
  
                      Numpy array to which numpy array `X` is compared.  For each 
                      element of `X`, ask if it is in `Y`.
  
      **Returns**
  
              **b** :  numpy array (bool)
  
                      Boolean numpy array, `len(b) = len(X)`.
  
      **See Also:**
  
              :func:`tabular.fast.recarrayisin`, 
              :func:`tabular.fast.arraydifference`