CODEWITHSUNDEEP
pythoninsert
Russell
Russell

Reputation: 3465

Insert bytearray into bytearray Python

I'm trying to insert one byte array into another at the beginning. Here's a simple example of what I'm trying to accomplish.

import struct
a = bytearray(struct.pack(">i", 1))
b = bytearray(struct.pack(">i", 2))
a = a.insert(0, b)
print(a)

However this fails with the following error:

a = a.insert(0, b) TypeError: an integer is required

Upvotes: 9

Views: 18536

Answers (3)

Fabio Teixeira
Fabio Teixeira

Reputation: 76

Bytearray are mutable sequence of single bytes (integers), so bytearray only accepts integers that meet the value restriction 0 <= x <= 255):

>>> a = bytearray(struct.pack(">i", 1))
>>> b = bytearray(struct.pack(">i", 2))
>>> a.insert(0,b)
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
TypeError: an integer is required

>>> a=b+a
>>> a
bytearray(b'\x00\x00\x00\x02\x00\x00\x00\x01')

>>>a[:2]=b
>>> a
bytearray(b'\x00\x00\x00\x02\x00\x01')

Upvotes: 1

juanpa.arrivillaga
juanpa.arrivillaga

Reputation: 96350

bytearray is a sequence-type, and it supports slice-based operations. The "insert at position i" idiom with slices goes like this x[i:i] = <a compatible sequence>. So, for the fist position:

>>> a
bytearray(b'\x00\x00\x00\x01')
>>> b
bytearray(b'\x00\x00\x00\x02')
>>> a[0:0] = b
>>> a
bytearray(b'\x00\x00\x00\x02\x00\x00\x00\x01')

For the third position:

>>> a
bytearray(b'\x00\x00\x00\x01')
>>> b
bytearray(b'\x00\x00\x00\x02')
>>> a[2:2] = b
>>> a
bytearray(b'\x00\x00\x00\x00\x00\x02\x00\x01')

Note, this isn't equivalent to .insert, because for sequences, .insert inserts the entire object as the ith element. So, consider the following simple example with lists:

>>> y = ['a','b']
>>> x.insert(0, y)
>>>
>>> x
[['a', 'b'], 1, 2, 3]

What you really wanted was:

>>> x
[1, 2, 3]
>>> y
['a', 'b']
>>> x[0:0] = y
>>> x
['a', 'b', 1, 2, 3]

Upvotes: 15

ezod
ezod

Reputation: 7421

>>> a = bytearray(struct.pack(">i", 1))
>>> b = bytearray(struct.pack(">i", 2))
>>> a = b + a
>>> a
bytearray(b'\x00\x00\x00\x02\x00\x00\x00\x01')

Upvotes: 1

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