`set_key` does not handle single quote `'` inside value properly

Start at the set_key entry point and reproduce the issue with the Python script in this report, then source the generated .env file in Bash. Trace how values are quoted and escaped, including the related PR discussion and warning about dotenv parsing. Done means a value containing a single quote is written in a form that both Bash can source and dotenv can parse correctly.

Problem

set_key function does not properly handle single quote ' inside value.

python-dotenv version: 1.0.1

Related PR

• https://github.com/theskumar/python-dotenv/pull/330 (https://github.com/theskumar/python-dotenv/pull/330#discussion_r669439596)

How to reproduce

1. Run python script below
2. Run source .env

Python Script

from dotenv import set_key

def main():
    var_value = "I'm a bug :("
    set_key(".env", "VAR", var_value)


if __name__ == "__main__":
    main()

Error from source .env

bash: .env: line 1: syntax error near unexpected token `('
bash: .env: line 1: `VAR='I\'m a bug :(''

Example of fix

⚠️ this fix produces values that dotenv cannot parse (see this issue) ⚠️

from dotenv import set_key

def fixed_set_key(file_path, key, value):
    # properly escape ' if present
    # https://stackoverflow.com/questions/8254120/how-can-i-escape-a-single-quote-in-a-single-quote-string-in-bash/26165123#26165123
    value = value.replace("'", "'\"'\"'")
    
    set_key(file_path, key, f"'{value}'", quote_mode="never")

def main():
    var_value = "I'm a fixed :)"
    fixed_set_key(".env", "VAR", var_value)


if __name__ == "__main__":
    main()