efficient use of ustruct.unpack?

[mathieu]

Dear all,

I've been trying for a while to read values from a binary file containing unsigned short integers ('H'), without much success beyond reading and appending each value in a for loop. There must be a better option...

What is the most efficient way to read from such a file and output an array('H')?

Thanks in advance,

- Mathieu

[cefn]

Hard to know what you've done, what you're trying to do.

You say you are without much success, but then seem to go on and say that you are successfully reading values. What is it that you can't do?

No code or console output provided to give us a clue what you are doing.

Could you share a bit more about your situation with clarity, please?

[OutoftheBOTS_]

very easy you can unpack muitlpe items at once even if they r different types, for you it will be even easier as they r all the same types.

Something like this will unpack 100 integers into an array

Code: Select all

format_string = "H" * 100
array_of_intergers = ustruct.unpack (format_string, string_2b_unpacked)

[deshipu]

If it was cpython, the most efficient way would be https://docs.python.org/2/library/array ... y.fromfile

[mathieu]

Hard to know what you've done, what you're trying to do.

You say you are without much success, but then seem to go on and say that you are successfully reading values. What is it that you can't do?

No code or console output provided to give us a clue what you are doing.

Could you share a bit more about your situation with clarity, please?

Sorry, I believed I was clear enough. I was trying to do something like this:

Code: Select all

import array, ustruct

with open('data.bin', 'wb') as f :
	for x in range(100) :
		f.write( ustruct.pack('H', x) )

with open('data.bin', 'rb') as f :
	data = array.array('H', ustruct.unpack('H', f.read()))

And of course I was not getting the expected results because of my incorrect ustruct format specifier ('H' instead of 'H'*100), as pointed out by OutoftheBOTS_. Thanks for taking the time to reply.

very easy you can unpack muitlpe items at once even if they r different types, for you it will be even easier as they r all the same types.

Something like this will unpack 100 integers into an array

Code: Select all

format_string = "H" * 100
array_of_intergers = ustruct.unpack (format_string, string_2b_unpacked)

Duh. Of course! Thanks a lot.

If it was cpython, the most efficient way would be https://docs.python.org/2/library/array ... y.fromfile

Yes, that's what I tried first. I really wish that array.array.fromfile() were available in uPython!

Thanks again everyone,

- Mathieu

[SpotlightKid]

Code: Select all

format_string = "H" * 100
array_of_intergers = ustruct.unpack (format_string, string_2b_unpacked)

A better way is this:

Code: Select all

>>> import ustruct as struct
>>> struct.pack('10H', *range(10))
b'\x00\x00\x01\x00\x02\x00\x03\x00\x04\x00\x05\x00\x06\x00\x07\x00\x08\x00\t\x00'
>>> struct.unpack('10H', _)
(0, 1, 2, 3, 4, 5, 6, 7, 8, 9)

i.e. just prefix the format char with the number of elements.