[I cannot use numpy so please refrain from talking about it]

I (apparently naively) thought Python array.frombytes() would read from a series of bytes representing various machine format integers, depending on how you create the array object. On creation you are required to provide a letter type code telling it (or so I thought) the machine type of integer making up the byte stream.

import array

b = b"\x01\x00\x02\x00\x03\x00\x04\x00"
a = array.array('i') #signed int (2 bytes)
a.frombytes(b)
print(a)

array('i', [131073, 262147])

and in the debugger:
array('i', [131073, 262147])
    itemsize: 4
    typecode: 'i'

The bytes in b are a series of little endian int16s (type code = 'i'). Despite being told this, it interpreted the bytes as 4-byte integers. This is Python 3.7.8.

I really need to convert the varying ints into an array (or list) of Python ints to deal with image data coming in byte-streams but which is actually either 16-bit or 32-bit integer, or 64 bit double floating format. What did I miss or do wrong? Or what is the right way to accomplish this?

CodePudding user response：

Note that the documentation doesn't specify the exact size of each type, it specifies the minimum size. Which means it may use a larger size if it wants, probably based on the types in the C compiler that was used to build Python.

Here are all the sizes on my system:

for c in 'bBuhHiIlLqQfd':
    print(c, array(c).itemsize)

b 1
B 1
u 2
h 2
H 2
i 4
I 4
l 4
L 4
q 8
Q 8
f 4
d 8

I would suggest using the 'h' or 'H' type.