Python: Indexing bytes array returns an integer

Question

Below is a sample interaction in Python 3.3

>>> bArray = bytes(b'ABCDE')
>>> bArray
b'ABCDE'
>>> bArray[0]
65
>>> type(bArray[0])
<class 'int'>
>>> bArray[0:1]
b'A'
>>> type(bArray[0:1])
<class 'bytes'>
>>> struct.pack('B', bArray[1])
b'B'
>>> type(struct.pack('B', bArray[1]))
<class 'bytes'>

It shows that indexing a bytes array yields an integer while slicing the same returns a bytes object.

Can anyone please explain me why is it so? Shouldn't indexing, too, return a byte object?
Is using byte more memory/performance efficient that using plain integers, provided the application is guaranteed to use numbers [0,255]?

M4ks · Accepted Answer · 2015-03-27 11:14:27Z

10

A quote from the manual

Warning While string objects are sequences of characters (represented by strings of length 1), bytes and bytearray objects are sequences of integers (between 0 and 255), representing the ASCII value of single bytes. That means that for a bytes or bytearray object b, b[0] will be an integer, while b[0:1] will be a bytes or bytearray object of length 1. The representation of bytes objects uses the literal format (b'...') since it is generally more useful than e.g. bytes([50, 19, 100]). You can always convert a bytes object into a list of integers using list(b).

So there is no "byte" object anymore.

The only explanation I could find was that bytes sequences are more memory efficient and less computation efficient - because all operations require conversion to ints anyway (even internally)

answered Mar 27, 2015 at 11:14

M4ks

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2 Comments

BrendanSimon Over a year ago

it might be that bytes (byte sequences) are hashable, compared to a list of integers (0-255) ? Then again, a tuple of integers (0-255) should be hashable.

BrendanSimon Over a year ago

BTW, I agree that it is confusing. I too expected a single index to produce 1 item of the same type of the array, not an integer .... sigh !!

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