Black for specific line from a specific file.

black_selection.py

# How to invoke this file would be to run something like this in your terminal:
# python3 black_selection.py /path/to/black/executable /path/to/file LineStart LineEnd
#
# Make sure to install black with the current running python version.
# To enable debug/verbose, check for BLACK-SELECTION-DEBUG environment and make sure it is set to True.
#
# To get the executable path, run the following command in your terminal:
# - Windows: where black
# - Linux/macOS: which black

import os
import sys
import random
import string
import subprocess

debug = os.environ.get('BLACK-SELECTION-DEBUG', 'False').lower() == 'true'

try:
    if debug:
        print('Trying to import black...')

    import black
except ImportError:
    raise ImportError(
        "Please install black with the current running python version before running this script.") from None

try:
    if debug:
        print('Trying to get black executable...')

    black_executable = sys.argv[0]

    subprocess.call([black_executable, '--version'])
except Exception: # (IndexError, Exception)
    raise IndexError("Please provide the path to the black executable.") from None

try:
    if debug:
        print('Trying to get file to run black on...')

    input_file = sys.argv[1]
except IndexError:
    raise IndexError("Please provide the path to the file to be formatted.") from None

try:
    if debug:
        print('Trying to get start line number to format...')

    start_line = sys.argv[2]
except IndexError:
    raise IndexError("Please provide the line number to start formatting from.") from None

try:
    if debug:
        print('Trying to get end line number to format...')

    end_line = sys.argv[3]
except IndexError:
    raise IndexError("Please provide the line number to end formatting at.") from None

code = []

# Read selected lines and write to tmpfile
if debug:
    print('Reading input file...')

with open(input_file, 'r') as f:
    lines = f.readlines()

    if debug:
        print('Getting selected lines to format...')

    for i in range(int(start_line), int(end_line) + 1):
        code.append(lines[i])

code = '\n'.join(code)

# Create our tmpfile and write our code to it
if debug:
    print('Making tmpfile...')

tmpfile = ''.join(random.choices(string.ascii_letters + string.digits, k=15)) + '.py'

with open(tmpfile, 'w') as f:
    f.write(code)

# Storing how many indents per line we have in our code
line_indent = []

# Un-indent the tmpfile for black to work properly
if debug:
    print('Un-indenting tmpfile\'s code...')

with open(tmpfile, 'r+') as f:
    lines = f.readlines()
    
    for line in lines:
        line_indent.append(len(line) - len(line.lstrip()))
        f.write(line.lstrip())

# Apply Black formatting to tmpfile
if debug:
    print('Running black on tmpfile...')

subprocess.call([black_executeable, tmpfile])

# Write back to tmpfile with correct indentation
if debug:
    print('Indenting tmpfile\'s code according to black\'s code formatting suggestions...')

with open(tmpfile, 'r+') as f:
    lines = f.readlines()
    
    for i, line in enumerate(lines):
        f.write(' ' * line_indent[i] + line)

# Delete original lines from file and insert newly formatted lines
if debug:
    print('Writing back to input file...')

with open(input_file, 'r+') as f:
    lines = f.readlines()

    with open(tmpfile, 'r') as f2:
        tmp_lines = f2.readlines()

        for i in range(int(start_line), int(end_line) + 1):
            lines[i] = tmp_lines[i - int(start_line)]

    f.write('\n'.join(lines))

# Finally, remove the tmp file
if debug:
    print('Removing tmpfile...')

os.remove(tmpfile)

if debug:
    print('Process Finished.')

# Now the black formatting has been published to the file.
# Make sure to report to https://gist.github.com/proguy914629bot/55c5d3d8a0c18787cdc8ae6bffcf1a2a for issues that you faced.