CODEWITHSUNDEEP
pythonbytearrays
IAbstract
IAbstract

Reputation: 19871

Convert byte string to bytes or bytearray

I have a string as follows:

  b'\x00\x00\x00\x00\x07\x80\x00\x03'

How can I convert this to an array of bytes? ... and back to a string from the bytes?

Upvotes: 38

Views: 117887

Answers (3)

MisterMiyagi
MisterMiyagi

Reputation: 50076

There is generally no need to do this. The string-like ASCII representation of bytes is just that, a representation. A bytes object, as e.g. created by a b-string literal, already is an (immutable, fixed size) array of bytes.

While bytes literals and representations are based on ASCII text, bytes objects actually behave like immutable sequences of integers, with each value in the sequence restricted such that 0 <= x < 256.

-- Python Built-in Types: Bytes Objects

For example, one can index a bytes object to get a specific byte datum or iterate a bytes object to work with every individual byte.

>>> blob = b"\x00\x00\x00\x00\x07\x80\x00\x03"
>>> blob[0], blob[-1]   # index to get specific byte
(0, 3)
>>> for datum in blob:  # iterate over each byte
...     if datum:
...         print(datum)
7
128
3

If mutability is required, bytearray is the appropriate type. This also supports all mutable sequence methods, such as assignment by index or the .append method.

One can efficiently convert between mutable and immutable bytes by simply passing them to the appropriate class. For example, bytearray(b"\x00\x00\x07\x80\x00\x03") creates a mutable array of bytes out of a bytes literal.

Note that both bytes and bytearray are optimised for holding byte elements. The objects have a backing memory buffer of an actual byte array as one would use in a C-like language.

+ <bytes> +    +-------------------
| *buffer | -> | \x00 \x03 \x00 ...
| ...     |    +-------------------
+---------+

In contrast, general purpose containers of bytes, say a list[int] or even list[bytes], use the full Python representation for elements. Instead of storing an array of byte data, they store a sequence of references to Python objects that in turn refer to an individual byte datum each.

+ <list> ---+    +-------------------
| *elements | -> | *0   *1   *2   ...
| ...       |    +-------------------
+-----------+       /    |
                   /     |
                  v      v
        + <int> --+  + <int> --+
        | *digits |  | *digits | -> +---+
        | ...     |  | ...     |    | 1 |
        +---------+  +---------+    +---+

Thus, converting bytes to list or similar should be avoided unless absolutely necessary.

Upvotes: 3

RafaelCaballero
RafaelCaballero

Reputation: 1613

From string to array of bytes:

a = bytearray.fromhex('00 00 00 00 07 80 00 03')

or 

a = bytearray(b'\x00\x00\x00\x00\x07\x80\x00\x03')

and back to string:

key = ''.join(chr(x) for x in a)

Upvotes: 16

steel.ne
steel.ne

Reputation: 713

in python 3:

>>> a=b'\x00\x00\x00\x00\x07\x80\x00\x03'
>>> b = list(a)
>>> b
[0, 0, 0, 0, 7, 128, 0, 3]
>>> c = bytes(b)
>>> c
b'\x00\x00\x00\x00\x07\x80\x00\x03'
>>>

Upvotes: 47

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