CODEWITHSUNDEEP
python-3.xunix
daveruinseverything
daveruinseverything

Reputation: 5167

Remove ANSI escape sequences when redirecting python output

I'm putting together a teaching project in which students will reimplement the grep utility in python. One feature I wanted to implement grep's ability to output matching text in color. To do this, I used ANSI escape sequences:

# min_example.py
START = '\033[91m'
END = '\033[0m'

some_line = f'this is {START}matching{END} text'
print(some_line)

It works exactly as expected. However, when piping the output to a text file, the raw escape sequences are included:

$ python min_example.py > test.txt
$ vi test.txt
this is ^[[91mmatching^[[0m text

The real grep utility manages to output color to the terminal, yet its output can be piped to a text file without any funky escape sequence characters being included.

So my question: what is grep doing differently here, and how can I reproduce it so that I can output color yet still have "pipe-able" output?

Upvotes: 1

Views: 1110

Answers (1)

daveruinseverything
daveruinseverything

Reputation: 5167

Turns out this is because grep isn't enabling color output when being piped. Its --color=auto option only enables color output if stdout is connected to a terminal. Running the same test with grep --color=always ... also results in ANSI escape characters being written to the text file.

I solved this problem by testing for sys.stdout.isatty() before adding ANSI escape codes

Upvotes: 1

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