[herniqeu]

set_key() writes the key exactly as it is given, but the unquoted key grammar only accepts [^=#\s]+. A key with a space, a # or an = therefore produces a line the parser cannot read, and the variable is lost without any error:

>>> set_key('.env', 'MY VAR', 'x')
>>> dotenv_values('.env')
{}
# python-dotenv could not parse statement starting at line 1

Same for A#B and A=B — all 13 values I tried disappeared. The call reports success, so a script that builds key names from labels writes a .env that silently misses the variable.

The parser already knows how to read a quoted key ('A B'='x' comes back as {'A B': 'x'}), so set_key() now quotes the key whenever it contains whitespace, # or =:

>>> set_key('.env', 'MY VAR', 'x')
>>> dotenv_values('.env')
{'MY VAR': 'x'}

Two keys remain impossible to represent, and now raise ValueError instead of writing a line that will be dropped: an empty key, and a key that needs quoting and contains a ' (the quoted-key grammar has no escape for it). A key that can be written unquoted is left exactly as before, and updating an existing quoted key rewrites that one line in place, keeping the rest of the file byte for byte.

Tests

• keys with a space, a #, an = and a tab survive set_key → get_key, and the line after them is not swallowed;
• an existing quoted key is updated in place ('a b'='old' → 'a b'='new', c=1 untouched);
• an empty key and a b'c raise ValueError.

On main those seven tests fail; tests/test_main.py goes from 153 to 160 passing with the change. (tests/test_cli.py still has failures from $HOME handling in this sandbox, unrelated.)

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Written with AI assistance.