NumPy `fromstring` function works fine in Python 2.7 but returns error in Python 3.7

Question

I use this syntax to convert the byte array dataword (2 bytes for each sample):

data = numpy.fromstring(dataword, dtype=numpy.int16)

same instruction in Python 3.7 returns the error:

TypeError: fromstring() argument 1 must be read-only bytes-like object, not memoryview

dataword = scope.ReadBinary(rlen-4) #dataword is a byte array, each 2 byte is an integer
data = numpy.fromstring(dataword, dtype=numpy.int16)# data is the int16 array

This is the content of data in Python 2.7.14:

[-1.41601562 -1.42382812 -1.42578125 ...,  1.66992188  1.65234375  1.671875  ]

I am expecting to get the same result with Python 3.7.

How am I supposed to use numpy.fromstring() in 3.7?

scope is an activex object, needed the receive the binary vector from an instrument. in python 2.7.14 dataword is defined as a binary array: buffer: ��P��0��@�p��p��........... — Maurizio Mastrofini
– Maurizio Mastrofini, Commented Mar 28, 2019 at 12:58
python 3.7: in the variable tab of LIclipse i can see that dataword is defined as memoryview:<memory at 0x0f..... definetely not a binary vector as in python 2.17 — Maurizio Mastrofini
– Maurizio Mastrofini, Commented Mar 28, 2019 at 13:33

mossymountain · Accepted Answer · 2019-03-27 16:48:01Z

1

The TypeError tries to tell you that dataword is of the non-supported type memoryview.
It needs to be passed as an unmutable type, like bytes:

data = numpy.fromstring(dataword.tobytes(), dtype=numpy.int16)

Even better; it seems like scope is a file-like object, so this could also work:

data = numpy.fromfile(scope, dtype=numpy.int16, count=rlen//2-4)

edited Mar 27, 2019 at 16:48

answered Mar 27, 2019 at 13:23

mossymountain

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Maurizio Mastrofini Over a year ago

Understood, all based on the how python3 is handling binary strings. I beleive this will work, going to try and give you an answer. Thanks

Maurizio Mastrofini · Accepted Answer · 2019-03-29 11:10:13Z

1

simple solution... found reading numpy manual: replace fromstring with frombuffer

data = numpy.frombuffer(dataword, dtype=numpy.int16) works perfectly

answered Mar 29, 2019 at 11:10

Maurizio Mastrofini

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Maurizio Mastrofini · Accepted Answer · 2023-09-15 10:49:38Z

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fromstring doesn't work because dataword is a memeoryview not a string, then frombuffer musty be used

data = numpy.frombuffer(dataword.tobytes(), dtype=numpy.int16)

answered Sep 15, 2023 at 10:49

Maurizio Mastrofini

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