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appending to a bytearray - Printable Version

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appending to a bytearray - Skaperen - Mar-09-2023

i cannot find a way to append a bytes string to a bytearray other than += operator. is that the way it has to be done? bytearray.append() gives an error exception message saying it wants an int. apparently it only takes one at a time:
Output:
>>> ab=bytearray(b'foobar')
>>> ab.append(120)
>>> ab
bytearray(b'foobarx')
>>> ab.append(121,122)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: append() takes exactly one argument (2 given)
>>> ab.append([121,122])
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: 'list' object cannot be interpreted as an integer
>>> ab.append(121)
>>> ab.append(122)
>>> ab
bytearray(b'foobarxyz')
>>>


RE: appending to a bytearray - deanhystad - Mar-09-2023

It is just like a list. append() for adding 1 value, extend() for adding many.
x = bytearray(b"bytes")
x.extend(b" and more bytes")
print(x)
Output:
bytearray(b'bytes and more bytes')


RE: appending to a bytearray - Skaperen - Mar-09-2023

thank you. i was thinking of a string, such as bytearray, as "one" value, so i never thought of .extend().

RE: appending to a bytearray - Skaperen - Mar-09-2023

another way to extend a bytearray is with a slice:
Output:
lt1a/forums/3 /home/forums 13> py
Python 3.8.10 (default, Nov 14 2022, 12:59:47) 
[GCC 9.4.0] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> x = bytearray(b"bytes")
>>> x[len(x):]=b" and more bytes"
>>> print(x)
bytearray(b'bytes and more bytes')
>>>
an even uglier way:
Output:
>>> print(x)
bytearray(b'bytes and more bytes')
>>> x[:]=x+b'and even more bytes'
>>> print(x)
bytearray(b'bytes and more bytesand even more bytes')
>>>
but it's not that much uglier. and i bet these ways can be done with list (and tuples?).

edit:

yeah, i should'a put a space in there.

RE: appending to a bytearray - deanhystad - Mar-09-2023

A bytes object is one object, but so is a list. Both are iterable which is why they can be used as an argument to extend().

RE: appending to a bytearray - Skaperen - Mar-10-2023

(Mar-09-2023, 11:47 PM)deanhystad Wrote: A bytes object is one object, but so is a list. Both are iterable which is why they can be used as an argument to extend().
can i use any iterator that produces the expected types (just about anything for a list) as an argument in .extend()?

RE: appending to a bytearray - deanhystad - Mar-10-2023 

Output:
>>> help(bytearray.extend)
Help on method_descriptor:

extend(self, iterable_of_ints, /)
    Append all the items from the iterator or sequence to the end of the bytearray.

    iterable_of_ints
      The iterable of items to append.


RE: appending to a bytearray - Skaperen - Mar-10-2023

what did i do wrong with this? how do i fix it?
Output:
>>> 
>>> b=bytearray()
>>> for x in bytearray(b'abc'):
...     b.extend(x)
... 
Traceback (most recent call last):
  File "<stdin>", line 2, in <module>
TypeError: can't extend bytearray with int
>>>


RE: appending to a bytearray - deanhystad - Mar-11-2023

x is a byte. b'abc' is iterable.. You append(byte) and extend(iterable)

RE: appending to a bytearray - Skaperen - Mar-12-2023

so, how do i fix b.extend(x) to make it work, such that b ends up with whatever followed in in the loop control?