In Flask-migrate ValueError: invalid interpolation syntax in connection string at position 15

I am using flask migrate to for database creation & migration in flask with flask-sqlalchemy.

Everything was working fine until I changed my database user password contains '@' then it stopped working so, I updated my code based on Writing a connection string when password contains special characters

It working for application but not for flask-migration, Its showing error while migrating

i.e on python manage.py db migrate

ValueError: invalid interpolation syntax in u'mysql://user:p%40ssword@localhost/testdb' at position 15

Here password is p@ssword and its escaped by urlquote (see above question link).

Full error stack:

Traceback (most recent call last):
  File "manage.py", line 20, in <module>
    manager.run()
  File "/usr/local/lib/python2.7/dist-packages/flask_script/__init__.py", line 412, in run
    result = self.handle(sys.argv[0], sys.argv[1:])
  File "/usr/local/lib/python2.7/dist-packages/flask_script/__init__.py", line 383, in handle
    res = handle(*args, **config)
  File "/usr/local/lib/python2.7/dist-packages/flask_script/commands.py", line 216, in __call__
    return self.run(*args, **kwargs)
  File "/usr/local/lib/python2.7/dist-packages/flask_migrate/__init__.py", line 177, in migrate
    version_path=version_path, rev_id=rev_id)
  File "/usr/local/lib/python2.7/dist-packages/alembic/command.py", line 117, in revision
    script_directory.run_env()
  File "/usr/local/lib/python2.7/dist-packages/alembic/script/base.py", line 407, in run_env
    util.load_python_file(self.dir, 'env.py')
  File "/usr/local/lib/python2.7/dist-packages/alembic/util/pyfiles.py", line 93, in load_python_file
    module = load_module_py(module_id, path)
  File "/usr/local/lib/python2.7/dist-packages/alembic/util/compat.py", line 79, in load_module_py
    mod = imp.load_source(module_id, path, fp)
  File "migrations/env.py", line 22, in <module>
    current_app.config.get('SQLALCHEMY_DATABASE_URI'))
  File "/usr/local/lib/python2.7/dist-packages/alembic/config.py", line 218, in set_main_option
    self.set_section_option(self.config_ini_section, name, value)
  File "/usr/local/lib/python2.7/dist-packages/alembic/config.py", line 245, in set_section_option
    self.file_config.set(section, name, value)
  File "/usr/lib/python2.7/ConfigParser.py", line 752, in set
    "position %d" % (value, tmp_value.find('%')))
ValueError: invalid interpolation syntax in u'mysql://user:p%40ssword@localhost/testdb' at position 15

Please help

In the migrations/env.py file, you will find the code that is responsible for this issue.

config.set_main_option('sqlalchemy.url',
                       current_app.config.get('SQLALCHEMY_DATABASE_URI'))

If there are % signs in the SQLALCHEMY_DATABASE_URI, this will cause an error.

You can solve this by editing the migrations/env.py file, and changing the offending line as follows

db_url_escaped = current_app.config.get('SQLALCHEMY_DATABASE_URI').replace('%', '%%')
config.set_main_option('sqlalchemy.url', db_url_escaped)

Also see the documentation of set_main_option:

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.