Bug: crash when DB password contains non-alphanumeric characters

[motus]

I think this an Alembic bug; I plan to open an issue with Alembic and link it here.

Update:
Alembic Config.set_main_option() documentation actually warns about this behavior:

Note that this value is passed to ConfigParser.set, which supports variable interpolation using pyformat (e.g. %(some_value)s). A raw percent sign not part of an interpolation symbol must therefore be escaped, e.g. %%. The given value may refer to another value already in the file using the interpolation format.

---

Python trace:

  File "/Users/sergiym/devel/MLOS/mlos_bench/mlos_bench/storage/sql/storage.py", line 46, in __init__
    self._init_engine()
    ~~~~~~~~~~~~~~~~~^^
  File "/Users/sergiym/devel/MLOS/mlos_bench/mlos_bench/storage/sql/storage.py", line 56, in _init_engine
    self.update_schema()
    ~~~~~~~~~~~~~~~~~~^^
  File "/Users/sergiym/devel/MLOS/mlos_bench/mlos_bench/storage/sql/storage.py", line 132, in update_schema
    self._schema.update()
    ~~~~~~~~~~~~~~~~~~~^^
  File "/Users/sergiym/devel/MLOS/mlos_bench/mlos_bench/storage/sql/schema.py", line 424, in update
    alembic_cfg = self._get_alembic_cfg(conn)
  File "/Users/sergiym/devel/MLOS/mlos_bench/mlos_bench/storage/sql/schema.py", line 355, in _get_alembic_cfg
    alembic_cfg.set_main_option(
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~^
        "sqlalchemy.url",
        ^^^^^^^^^^^^^^^^^
    ...<2 lines>...
        ),
        ^^
    )
    ^
  File "/opt/anaconda3/envs/mlos/lib/python3.13/site-packages/alembic/config.py", line 269, in set_main_option
    self.set_section_option(self.config_ini_section, name, value)
    ~~~~~~~~~~~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/opt/anaconda3/envs/mlos/lib/python3.13/site-packages/alembic/config.py", line 296, in set_section_option
    self.file_config.set(section, name, value)
    ~~~~~~~~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^
  File "/opt/anaconda3/envs/mlos/lib/python3.13/configparser.py", line 1236, in set
    super().set(section, option, value)
    ~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^
  File "/opt/anaconda3/envs/mlos/lib/python3.13/configparser.py", line 923, in set
    value = self._interpolation.before_set(self, section, option,
                                           value)
  File "/opt/anaconda3/envs/mlos/lib/python3.13/configparser.py", line 422, in before_set
    raise ValueError("invalid interpolation syntax in %r at "
                     "position %d" % (value, tmp_value.find('%')))
ValueError: invalid interpolation syntax in 'postgresql+psycopg2://mlos:****%23********@sergiym-workid-bench.postgres.database.azure.com:5432/mlos_bench' at position 27

Note the URL postgresql+psycopg2://username:****%23********@hostname:5432/dbname in the last line (password redacted). Non-alphanumeric characters get urlencoded (e.g., # becomes %23) and conflict with python % operator string interpolation in Alembic.

The problem persists after upgrading Alembic from 1.15.2 to the most recent version 1.16.5.