[Tutor] Help with building bytearray arrays

[Chip Wachob]

On Sat, Sep 8, 2018 at 9:14 PM, Cameron Simpson <cs at cskk.id.au> wrote:
> On 08Sep2018 11:40, Alan Gauld <alan.gauld at yahoo.co.uk> wrote:
>>
>> On 08/09/18 03:15, Chip Wachob wrote:
>>>
>>> Ideally, I'd like to take the slice_size chunks that have been read
>>> and concatenate them back togetjer into a long MAX_LOOP_COUNT size
>>> array to pass back to the rest of my code.  Eg:
>>
>>
>> You need to create a list of read_ary
>>
>> results = []
>>
>> then after creating each read_ary value append it
>> to results.
>>
>> results.append(read_ary)
>>
>> Then, at the very end, return the summation of all
>> the lists in results.
>>
>> return sum(results,[])
>

Cameron is correct (Gold Star for you Cameron)

>
> Actually he's getting back bytearray instances from transfer and wants to
> join them up (his function does a few small transfers to work around an
> issue with one big transfer). His earlier code is just confused. So he
> wants:
>
>  bytearray().join(results)
>
> Hacked example:
>
>  >>> bytearray().join( (bytearray("foo"),bytearray("bah")) )
>  bytearray(b'foobah')

I understand this example and I can replicate it in the interpreter..

But, I'm still missing something here.

I presume that I need to instantiate an array of slice_size-sized bytearrays.

So, when I'm looping through, I can do:

for i in range (0, slice_count):
   results[i] = spi.transfer(data_out)

Then I can :

all_together = butearray().join(results)

But I can't seem to be able to find the proper syntax to create the
initial array.

And any attempt at filling the arrays to test some stand-alone code
only give me errors.

Here's my code (all of it)

#
#
#

import sys

slice_size = 16    # in bytes
MAX_LOOP_COUNT = 64    # in bytes

slice_count = MAX_LOOP_COUNT / slice_size

print " slice size = ", slice_size
print " MLC = ", MAX_LOOP_COUNT
print " slice count = ", slice_count

#results = bytearray( (bytearray(slice_size)*slice_count) )
results = bytearray(slice_size)    # why isn't this 16 bytes long?

res_list = (results)*slice_count

print " results ", [results]
print " results size ", sys.getsizeof(results)
print " res_list ", [res_list]
print " res_list size ", sys.getsizeof(res_list)
print " type = ", type(results)

results[0] = ([1,3,5,7,9])

all_together = bytearray().join(results)

But I'm getting:

$ python merge_1.py
 slice size =  16
 MLC =  64
 slice count =  4
 results  [bytearray(b'\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00')]
 results size  65
 res_list  [bytearray(b'\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00')]
 res_list size  113
 type =  <type 'bytearray'>
Traceback (most recent call last):
  File "merge_1.py", line 27, in <module>
    results[0] = ([1,3,5,7,9])
TypeError: an integer or string of size 1 is required

Again, I feel like I'm circling the target, but not able to divine the
proper syntax

I hope this makes sense.


>
> And he's working with bytearrays because the target library is Python 2,
> where there's no bytes type.
>
> Cheers,
> Cameron Simpson <cs at cskk.id.au>
>
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