How to read a binary file and append them to a new file?

Question

I read data from a file as binary data like

with open(filename, "rb") as filein:
    content = filein.read()
print(type(content[0]))

and I expected the data type of the data read to be byte, but I get int.

How to read data from a file as type byte (i.e. the python structure where I put a "b" in from of i like

mybyte = b"bytes"

so I can "add" them to other byte strings?

What I actually want to do is essentially this:

# Read the complete(!) content of the file
with open(filename, "rb") as filein:
    content = filein.read()

# Create new content, where I manipulate some single bytes
# For simplicity this is not shown here
new_content = b""
for byte in content:
    # some manipulating of single bytes, omitted for simplicity
    new_content += byte

# Write the modified content again to a new file
# In this very example, it should replicate the exact same file
with open(filename + "-changed", "wb") as fileout:
    fileout.write(new_content)

But here I get an error

 Traceback (most recent call last):
  File "break_software.py", line 29, in <module>
    new_content += byte
TypeError: can't concat int to bytes

Python doesn't have a byte data type. It has byte strings, and the elements of byte strings are integers. — Barmar, Feb 03 '23 at 15:58
Then check `type(content)`. `type(content[0])` is analogous to `type(b"abc"[0])` (since `b""` is empty) — Pranav Hosangadi, Feb 03 '23 at 16:00
You seem to be assuming that since the elements of strings are 1-character strings, the elements of byte strings will be 1-byte byte strings. They didn't repeat that mistake. — Barmar, Feb 03 '23 at 16:00
Are you asking how to append to a `bytes`? If so please update your title and consider the following duplicate https://stackoverflow.com/q/27001419/843953 — Pranav Hosangadi, Feb 03 '23 at 16:06
Here I get then an error `TypeError: can't concat int to bytearray`. — Alex, Feb 03 '23 at 16:07
[Weird](https://tio.run/##K6gsycjPM/7/v6JYwVYhqbIkNbGoKLFSI0k9psLAEIiNgNhYXZOrolgvsaAgNS9Fw1STq6AoM69Eo6JY8/9/AA) — Pranav Hosangadi, Feb 03 '23 at 16:10
Ah sorry, when I use `new_content.append(..)` then it is working. I must not use `+=`. — Alex, Feb 03 '23 at 16:10

score 0 · Answer 1 · answered Feb 03 '23 at 15:59

0

This is how bytes works in python, consider that

mybyte = b"bytes"
print(mybyte[0])  # 98
print(type(mybyte[0]))  # <class 'int'>

answered Feb 03 '23 at 15:59

Daweo

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So how can I read the content of a file as "bytes"? – Alex Feb 03 '23 at 16:00
@Alex `content` is a `bytes` object. – Barmar Feb 03 '23 at 16:01
You could use `filein.read(1)` to read 1 byte at a time. – Barmar Feb 03 '23 at 16:02

How to read a binary file and append them to a new file?

1 Answers1