[36taransingh5-dotcom]

Problem

set_key writes values in single quotes intending to preserve them literally, but reading them back with dotenv_values/load_dotenv (which interpolate by default) still expands variable references inside single-quoted values. The value is silently corrupted:

from dotenv import set_key, dotenv_values

set_key(".env", "KEY", "a${X}b")
dotenv_values(".env")["KEY"]  # -> "ab" (X is undefined), not "a${X}b"

This is the round-trip data loss reported in #422.

Root cause

parser.Binding discarded the quote character before main.resolve_variables ran, so the resolver had no way to know a value was single-quoted.

Fix

• parser.parse_value now returns the quote character alongside the value, and Binding carries it in a new quote field.
• main.dict() uses a private _parse_full() that keeps the quote triples (the public parse() shape is unchanged).
• resolve_variables returns single-quoted values verbatim, matching POSIX shell semantics where single quotes inhibit expansion. The literal text of a single-quoted value remains visible to later values, consistent with the existing chained-resolution behaviour: with B='${A}' then C=${B}, C resolves to the literal text ${A}.

Interpolation of double-quoted and unquoted values is unchanged.

Test changes

• New cases cover the set_key round-trip and literal single-quote handling.
• One existing parametrized case was updated: ({"b": "c"}, "a='${b}'", True, ...) previously expected {"a": "c"} and now expects the literal {"a": "${b}"}. This is an intentional behaviour change implementing Unable to escape posix expansion #422; flagging it explicitly for review.

Fixes #422.

Developed with AI assistance.