Hello everyone,
I had quite some trouble figuring out the _correct_ way to create
heterogeneous arrays.
What I wanted to do was something like the following:
>>> numpy.array( [(0,0,0)], dtype={'names':['a','b','c'],
'formats':['f4','f4','f4']})
This works fine. Now, let's do something wrong, e.g. leave out the
'formats' specifier:
>>> numpy.array( [(0,0,0)], dtype={'names':['a','b','c']})
Traceback (most recent call last):
File "<stdin>", line 1, in ?
File "/usr/lib/python2.4/site-packages/numpy/core/_internal.py", line
53, in _usefields
names, formats, offsets, titles = _makenames_list(adict)
File "/usr/lib/python2.4/site-packages/numpy/core/_internal.py", line
21, in _makenames_list
raise ValueError, "entry not a 2- or 3- tuple"
ValueError: entry not a 2- or 3- tuple
This error message was totally unclear to me. After reading a little on
the scipy wiki I finally realized that (maybe) numpy internally converts
the dict with the names and the formats to a list of 2-tuples of the
form (name, format). Since no formats were given, these 2-tuples were
invalid.
I would suggest a check for the required dict keys and some meaningful
error message like: "The dtype dictionary must at least contain the
'names' and the 'formats' items."
Keep up the great work,
Niklas.
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