Consider the following:
a = np.array([(1, 'a'), (2, 'b'), (3, 'c')], dtype=[('foo', 'i'), ('bar', 'a1')])
b = np.append(a, (4, 'd'))
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
File "/home/ben/miniconda/lib/python2.7/site-packages/numpy/lib/function_base.py", line 3555, in append
return concatenate((arr, values), axis=axis)
TypeError: invalid type promotion
b = np.insert(a, 4, (4, 'd'))
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
File "/home/ben/miniconda/lib/python2.7/site-packages/numpy/lib/function_base.py", line 3464, in insert
new[slobj] = values
ValueError: could not convert string to float: d
In my original code snippet I was developing which has a more involved dtype, I actually got a different exception:
b = np.append(a, c)
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
File "/home/ben/miniconda/lib/python2.7/site-packages/numpy/lib/function_base.py", line 3553, in append
values = ravel(values)
File "/home/ben/miniconda/lib/python2.7/site-packages/numpy/core/fromnumeric.py", line 1367, in ravel
return asarray(a).ravel(order)
File "/home/ben/miniconda/lib/python2.7/site-packages/numpy/core/numeric.py", line 460, in asarray
return array(a, dtype, copy=False, order=order)
ValueError: setting an array element with a sequence.
The same happens whether I enclose the value with square bracket or not. I suspect that this array type just wasn't considered when its checking logic was developed. This is with 1.8.2 from miniconda. Should we consider this a bug or are structured arrays just not expected to be modified like this?