Correct way to change bytes in a file?

[snippsat]

In scenario-1, I assume blist[2] = hex 0B = decimal 11 is stored in memory.

id() show location in memory.
So bytes string are immutable,same as str string type.
Nothing get changed in memory,not allowed.

>>> b_string = b'\x76\x12\x0B\x08'
>>> [id(i) for i in b_string]
[1400293216, 1400291616, 1400291504, 1400291456]
>>> b_string[2] = 10
Traceback (most recent call last):
  File "<string>", line 301, in runcode
  File "<interactive input>", line 1, in <module>
TypeError: 'bytes' object does not support item assignment
>>> [id(i) for i in b_string]
[1400293216, 1400291616, 1400291504, 1400291456]

In scenario-2, I assume blist[2] is also hex 0B = decimal 11 stored in memory.

List are mutable so here get item 2 changed,the original 11(with memory location 1400291504),
will be garbage collect and replaced with 10(new memory location 1400291488).

>>> blist = list(b'\x76\x12\x0B\x08')
>>> [id(i) for i in blist]
[1400293216, 1400291616, 1400291504, 1400291456]
>>> blist[2] = 10
>>> [id(i) for i in blist]
[1400293216, 1400291616, 1400291488, 1400291456]

As mention you don't have to worry about how things are stored in memory.
Python clean up(garbage collect) stuff in memory for you