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?

Chiheb Nexus
– Chiheb Nexus

2017-06-02 11:38:53 +00:00
Commented Jun 2, 2017 at 11:38 — Chiheb Nexus
– Chiheb Nexus, Commented Jun 2, 2017 at 11:38

Epic Wink · Accepted Answer · 2020-01-21 07:39:24Z

0

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

edited Jan 21, 2020 at 7:39

answered Jun 2, 2017 at 11:36

Epic Wink

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1 Comment

Jean-François Fabre Over a year ago

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

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