Preserve quoted dotenv key names when setting values

CHANGELOG.md

@@ -9,6 +9,8 @@ project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
 
 ### Fixed
 
+- Preserve key names containing whitespace, `#`, or `=` when writing them with `set_key` or `dotenv set`.
+
 - Fix a package build deprecation warning caused by a non-string `license` value in `pyproject.toml` by [@kurtmckee] in [#648]
 - `set_key`, `unset_key` and the `dotenv set`/`unset` commands now name the `.env` path instead of an internal temporary file when its directory is missing or not writable, and the CLI prints a short error and exits with code 2 instead of a traceback by [@jamalkamaladdin] in [#711]
 - `set_key` and `unset_key` no longer leave a `.tmp_*` file behind on Windows when writing a read-only `.env` fails, and the error raised is the one from the failed write rather than from cleaning up the temporary file by [@MohammedAlkindi] in [#686]

src/dotenv/main.py

@@ -2,6 +2,7 @@
 import logging
 import os
 import pathlib
+import re
 import stat
 import sys
 import tempfile
@@ -234,6 +235,9 @@ def set_key(
     Adds or Updates a key/value to the given .env
 
     The target .env file is created if it doesn't exist.
+    Keys are quoted when required by the dotenv syntax, independently of
+    ``quote_mode``. A key that cannot be represented raises ``ValueError``
+    before the file is modified.
 
     This function doesn't follow symlinks by default, to avoid accidentally
     modifying a file at a potentially untrusted path. If you don't need this
@@ -246,6 +250,18 @@ def set_key(
     if quote_mode not in ("always", "auto", "never"):
         raise ValueError(f"Unknown quote_mode: {quote_mode}")
 
+    # Keys may be single-quoted in dotenv files, independently of value quoting.
+    if (
+        key_to_set
+        and not key_to_set.startswith("'")
+        and re.fullmatch(r"[^=#\s]+", key_to_set)
+    ):
+        key_out = key_to_set
+    elif key_to_set and "'" not in key_to_set:
+        key_out = f"'{key_to_set}'"
+    else:
+        raise ValueError("Unsupported dotenv key")
+
     quote = quote_mode == "always" or (
         quote_mode == "auto" and not value_to_set.isalnum()
     )
@@ -260,9 +276,9 @@ def set_key(
     else:
         value_out = value_to_set
     if export:
-        line_out = f"export {key_to_set}={value_out}\n"
+        line_out = f"export {key_out}={value_out}\n"
     else:
-        line_out = f"{key_to_set}={value_out}\n"
+        line_out = f"{key_out}={value_out}\n"
 
     with rewrite(dotenv_path, encoding=encoding, follow_symlinks=follow_symlinks) as (
         source,

tests/test_cli.py

@@ -415,3 +415,11 @@ def test_run_with_dotenv_and_command_flags(dotenv_path, tmp_path):
 
     check_process(result, exit_code=0)
     assert result.stdout.strip().startswith("dotenv, version")
+
+
+@pytest.mark.parametrize("key", ["APP NAME", "APP#NAME", "APP=NAME"])
+def test_set_quoted_key(cli, dotenv_path, key):
+    dotenv_path.write_text(f"'{key}'=old\nSAFE=untouched\n")
+    result = cli.invoke(dotenv_cli, ["--file", dotenv_path, "set", key, "new"])
+    assert result.exit_code == 0, result.output
+    assert dotenv.dotenv_values(dotenv_path) == {key: "new", "SAFE": "untouched"}

tests/test_main.py

@@ -948,3 +948,52 @@ def test_dotenv_values_empty_value_with_inline_comment(string, expected):
     result = dotenv.dotenv_values(stream=io.StringIO(string))
 
     assert result == expected
+
+
+@pytest.mark.parametrize(
+    "key", ["APP NAME", "APP#NAME", "APP=NAME", " APP ", "APP\tNAME"]
+)
+@pytest.mark.parametrize("existing", [False, True])
+@pytest.mark.parametrize("quote_mode", ["always", "auto", "never"])
+def test_set_key_round_trips_quoted_keys(dotenv_path, key, existing, quote_mode):
+    before = f"'{key}'=old\n" if existing else ""
+    dotenv_path.write_text(before + "SAFE=untouched\n")
+
+    assert dotenv.set_key(dotenv_path, key, "new", quote_mode=quote_mode) == (
+        True,
+        key,
+        "new",
+    )
+    assert dotenv.dotenv_values(dotenv_path) == {key: "new", "SAFE": "untouched"}
+    assert dotenv.get_key(dotenv_path, key) == "new"
+
+
+@pytest.mark.parametrize("key", ["", "'APP", "APP NAME'", "APP#NAME'"])
+def test_set_key_rejects_unrepresentable_keys_without_modifying_file(dotenv_path, key):
+    original = "SAFE=untouched\n"
+    dotenv_path.write_text(original)
+    with pytest.raises(ValueError, match="key"):
+        dotenv.set_key(dotenv_path, key, "new")
+    assert dotenv_path.read_text() == original
+
+
+@pytest.mark.parametrize("key", ["APP", "APP'NAME", 'APP"NAME', "APP-NAME", "APP.NAME"])
+def test_set_key_preserves_unquoted_key_spelling(dotenv_path, key):
+    dotenv.set_key(dotenv_path, key, "new")
+    assert dotenv_path.read_text() == f"{key}='new'\n"
+    assert dotenv.dotenv_values(dotenv_path) == {key: "new"}
+
+
+@pytest.mark.parametrize("key", ["APP NAME", "APP#NAME", "APP=NAME"])
+def test_set_key_export_round_trips_quoted_keys(dotenv_path, key):
+    dotenv.set_key(dotenv_path, key, "new", export=True)
+    assert dotenv_path.read_text() == f"export '{key}'='new'\n"
+    assert dotenv.dotenv_values(dotenv_path) == {key: "new"}
+
+
+@pytest.mark.parametrize("key", ["", "APP NAME'"])
+def test_set_key_rejects_unrepresentable_keys_without_creating_file(tmp_path, key):
+    path = tmp_path / "missing.env"
+    with pytest.raises(ValueError, match="key"):
+        dotenv.set_key(path, key, "new")
+    assert not path.exists()