TypeError when appending fields to a structured array of size ONE

Question

I'm getting a run-time error when trying to append field(s) to a structured array of size ONE. I've written a simple example below:

import numpy as np
import numpy.lib.recfunctions as rcfuncs

dtype_ = np.dtype( { 'names': ["field_a","field_b","field_c"]
                  , 'formats': ['S32', 'i4', 'f8']}
                  )
data_ = [("1",17, 123.45)]
numpy_array = np.array(data_, dtype_)            

# append 2 fields
numpy_array = rcfuncs.append_fields( numpy_array,["field_d","field_e"],data=[ "1","3" ] )

# append 1 field fails :(
numpy_array = rcfuncs.append_fields( numpy_array, "field_f", data=["123456"] )

I'm getting the error:

TypeError: descriptor 'ravel' requires a 'numpy.ndarray' object but received a 'numpy.void'

As well, if I 'invert' the appends, the statement with the two fields append will fail:

# append 1 field
numpy_array = rcfuncs.append_fields( numpy_array, "field_f", data=["123456"] )

# append 2 fields fails :(
numpy_array = rcfuncs.append_fields( numpy_array,["field_d","field_e"],data=[ "1", "3" ] )

I am running with python 2.7.11 and numpy 1.11.0 and I do not have the issue when the initial array is of size greater than 2.

How to solve the type error?

Thanks

Answer 1

We do not get the TypeError when setting the optional parameter usemask to False

numpy_array = \
  rcfuncs.append_fields(numpy_array, "field_f", data=["123456"], usemask=False)
numpy_array = \
  rcfuncs.append_fields(numpy_array,["field_d","field_e"],data=[ "1", "3" ], usemask=False)