How do I write binary data to a text file in Python?

Question

I need to write text, then binary data to a file. For example, I would like to write the file with contents:

BESTFORMAT
NUMLINES 42
FIELDS FOO BAR SPAM
DATATYPES INT32 FLOAT64 FLOAT64
FILETYPE BINARY
???d?'Ӈ T???'Ѥ??X??\??
?? R??&??X??\???????
??zR??X??\????????
...

However, in Python you can't open a file in a way that you can write ASCII data, then binary data.

I've tried:

Converting my binary data to text (no good, as it outputs b'5 42.7 0.8'
Encoding my text data to binary and opening the file as binary (no good, as then I have a binary file). Edit: it turns out this was working, but I needed to open the file in my text editor with UTF-8 encoding

Possible duplicate of [Python how to write to a binary file?](https://stackoverflow.com/questions/18367007/python-how-to-write-to-a-binary-file) — Chiheb Nexus, Jun 02 '17 at 11:38

Epic Wink · Answer 1 · 2020-01-21T07:39:24.510

Multiple solutions:

Write text data, then re-open in append binary mode and write binary data

with open("file", "w") as f:
    f.write("text")
with open("file", "ab") as f:
    f.write(b"bytes")

Convert the text data to bytes

with open("file", "wb") as f:
    f.write("text".encode())
    f.write(b"bytes")

Write the text data to a text wrapper

import io
with open("file", "wb") as f:
    f_text = io.TextIOWrapper(f, write_through=True)
    f_text.write("text")
    f.write(b"bytes")

Note: some text editors will see non-utf-8 bytes in the file and view the file in hexadecimal mode. To see the text, re-open the file in the text editor in UTF-8 encoding

you could have used `fl.write(b"BESTFORMAT\n\ NUMLINES 42\n\ FIELDS FOO BAR SPAM\n\ DATATYPES INT32 FLOAT64 FLOAT64\n\ FILETYPE BINARY\n\ ")` so you could have used the binary mode of the file — Jean-François Fabre, Jun 02 '17 at 11:40

How do I write binary data to a text file in Python?

1 Answers1