python - numpy structured arrays: help understanding output -

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i trying learn how use numpy's structured arrays. specifically, trying add information more 1 field @ time. tried:

import numpy np  numrec = np.zeros(8, dtype=[('col0', 'int16'), ('col1', 'int16'),                             ('col2', 'int16'), ('col3', 'int16')])  numrec[['col1','col2']][0:2] = [(3,5), (1,8)] print numrec

the above not work. values not added columns specified. surprising do not error when run it. can please explain happening?

thanks.

you setting values on temporary.

numrec[["col1", "col2"]]

returns copy of array. can see owndata flag.

>>> numrec[["col1", "col2"]].flags["owndata"] true

when index numpy array list, numpy returns copy of data. has copy, because, in general, list may not resolve regular, ordered view of underlying data. (this holds numpy array, not structured arrays.)

compare

>>> numrec[["col1"]].flags["owndata"] true >>> numrec["col1"].flags["owndata"] false

also, if numpy array view, base member holds underlying array.

>>> id(numrec["col1"].base) == id(numrec) true

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