What is equivalent of MATLAB's fread with skip parameter in Python?

Question

I wonder how can I implement MATLAB

fread(fileID,sizeA,precision,skip)

in Python (documentation). There are many advices how to deal with it in case of

fread(fileID,sizeA,precision)

but I need the skip parameter. So I want to obtain some

def fread(fileID,sizeA,precision,skip):
    # some code which do the same thing as matlab fread(fileID,sizeA,precision,skip)
    pass

How can it be implemented without symbol-wise reading?

Does this answer your question? What is the equivalent of 'fread' from Matlab in Python? — lhoupert
– lhoupert, Commented Jul 10, 2020 at 16:47
@llhoupert No, as I said it is all examples without implementing of skip parameter. It's crucial for me — Nourless
– Nourless, Commented Jul 10, 2020 at 16:52

mtrw · Accepted Answer · 2020-07-10 19:12:07Z

1

You can use Python's struct module to parse complex binary structures, including pad bytes. For instance, copying the Matlab doc, if you want to read a file of 2 short ints followed by 2 pad bytes:

import struct
fmt = "=hhxx" #native endianness and no alignment (=), two shorts (h), two pad bytes (x)
data = [x for x in struct.iter_unpack(fmt, open("nine.bin", "rb").read())]
## [(1, 2), (4, 5), (7, 8)]

Note that the output of struct.iter_unpack, and the other unpack methods, is a tuple.

answered Jul 10, 2020 at 19:12

mtrw

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2 Comments

Nourless Over a year ago

it raises a error iterative unpacking requires a buffer of a multiple of 6 bytes

mtrw Over a year ago

@Nourless - you need to create the file like in the MATLAB docs. fwrite(fileID,[1:9],'uint16'); creates a file of exactly 18 bytes.

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