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Python 3.9 Errors with MKDocs Serve

After upgrading to Python 3.9, i'm getting these errors when running mkdocs serve I'm not a developer. I use MKDocs to build a documentation site and I wanted to upgrade the software, as a result I had to upgrade Python, pip, mkdocs and mkdocs-material..
INFO - Cleaning site directory
Traceback (most recent call last):
File "/usr/local/bin/mkdocs", line 8, in <module>
sys.exit(cli())
File "/usr/local/lib/python3.9/site-packages/click/core.py", line 829, in __call__
return self.main(*args, **kwargs)
File "/usr/local/lib/python3.9/site-packages/click/core.py", line 782, in main
rv = self.invoke(ctx)
File "/usr/local/lib/python3.9/site-packages/click/core.py", line 1259, in invoke
return _process_result(sub_ctx.command.invoke(sub_ctx))
File "/usr/local/lib/python3.9/site-packages/click/core.py", line 1066, in invoke
return ctx.invoke(self.callback, **ctx.params)
File "/usr/local/lib/python3.9/site-packages/click/core.py", line 610, in invoke
return callback(*args, **kwargs)
File "/usr/local/lib/python3.9/site-packages/mkdocs/__main__.py", line 133, in serve_command
serve.serve(
File "/usr/local/lib/python3.9/site-packages/mkdocs/commands/serve.py", line 141, in serve
config = builder()
File "/usr/local/lib/python3.9/site-packages/mkdocs/commands/serve.py", line 136, in builder
build(config, live_server=live_server, dirty=dirty)
File "/usr/local/lib/python3.9/site-packages/mkdocs/commands/build.py", line 263, in build
nav = get_navigation(files, config)
File "/usr/local/lib/python3.9/site-packages/mkdocs/structure/nav.py", line 102, in get_navigation
items = _data_to_navigation(nav_config, files, config)
File "/usr/local/lib/python3.9/site-packages/mkdocs/structure/nav.py", line 157, in _data_to_navigation
return [
File "/usr/local/lib/python3.9/site-packages/mkdocs/structure/nav.py", line 158, in <listcomp>
_data_to_navigation(item, files, config)[0]
File "/usr/local/lib/python3.9/site-packages/mkdocs/structure/nav.py", line 150, in _data_to_navigation
return [
File "/usr/local/lib/python3.9/site-packages/mkdocs/structure/nav.py", line 153, in <listcomp>
Section(title=key, children=_data_to_navigation(value, files, config))
File "/usr/local/lib/python3.9/site-packages/mkdocs/structure/nav.py", line 164, in _data_to_navigation
file = files.get_file_from_path(path)
File "/usr/local/lib/python3.9/site-packages/mkdocs/structure/files.py", line 31, in get_file_from_path
return self.src_paths.get(os.path.normpath(path))
File "/usr/local/Cellar/python#3.9/3.9.0_1/Frameworks/Python.framework/Versions/3.9/lib/python3.9/posixpath.py", line 336, in normpath
path = os.fspath(path)
TypeError: expected str, bytes or os.PathLike object, not NoneType```

Try this.
pip install -U mkdocs
I was getting same error. After updated mkdocs it resolved.

How can I solve my connection error in mysql

I've tried to connect my db. All db settings in settings.py is checked and they are correct. When I run the server, I face an error which is shown below. I searched at internet and I find solutions but all them is working for lower python version. I am using the newest python version. My error is that:
System check identified no issues (0 silenced).
Exception in thread django-main-thread:
Traceback (most recent call last):
File "/Library/Frameworks/Python.framework/Versions/3.7/lib/python3.7/threading.py", line 917, in _bootstrap_inner
self.run()
File "/Library/Frameworks/Python.framework/Versions/3.7/lib/python3.7/threading.py", line 865, in run
self._target(*self._args, **self._kwargs)
File "/Library/Frameworks/Python.framework/Versions/3.7/lib/python3.7/site-packages/django/utils/autoreload.py", line 54, in wrapper
fn(*args, **kwargs)
File "/Library/Frameworks/Python.framework/Versions/3.7/lib/python3.7/site-packages/django/core/management/commands/runserver.py", line 120, in inner_run
self.check_migrations()
File "/Library/Frameworks/Python.framework/Versions/3.7/lib/python3.7/site-packages/django/core/management/base.py", line 453, in check_migrations
executor = MigrationExecutor(connections[DEFAULT_DB_ALIAS])
File "/Library/Frameworks/Python.framework/Versions/3.7/lib/python3.7/site-packages/django/db/migrations/executor.py", line 18, in __init__
self.loader = MigrationLoader(self.connection)
File "/Library/Frameworks/Python.framework/Versions/3.7/lib/python3.7/site-packages/django/db/migrations/loader.py", line 49, in __init__
self.build_graph()
File "/Library/Frameworks/Python.framework/Versions/3.7/lib/python3.7/site-packages/django/db/migrations/loader.py", line 212, in build_graph
self.applied_migrations = recorder.applied_migrations()
File "/Library/Frameworks/Python.framework/Versions/3.7/lib/python3.7/site-packages/django/db/migrations/recorder.py", line 73, in applied_migrations
if self.has_table():
File "/Library/Frameworks/Python.framework/Versions/3.7/lib/python3.7/site-packages/django/db/migrations/recorder.py", line 56, in has_table
return self.Migration._meta.db_table in self.connection.introspection.table_names(self.connection.cursor())
File "/Library/Frameworks/Python.framework/Versions/3.7/lib/python3.7/site-packages/django/db/backends/base/base.py", line 256, in cursor
return self._cursor()
File "/Library/Frameworks/Python.framework/Versions/3.7/lib/python3.7/site-packages/django/db/backends/base/base.py", line 233, in _cursor
self.ensure_connection()
File "/Library/Frameworks/Python.framework/Versions/3.7/lib/python3.7/site-packages/django/db/backends/base/base.py", line 217, in ensure_connection
self.connect()
File "/Library/Frameworks/Python.framework/Versions/3.7/lib/python3.7/site-packages/django/db/backends/base/base.py", line 197, in connect
self.init_connection_state()
File "/Library/Frameworks/Python.framework/Versions/3.7/lib/python3.7/site-packages/django/db/backends/mysql/base.py", line 231, in init_connection_state
if self.features.is_sql_auto_is_null_enabled:
File "/Library/Frameworks/Python.framework/Versions/3.7/lib/python3.7/site-packages/django/utils/functional.py", line 80, in __get__
res = instance.__dict__[self.name] = self.func(instance)
File "/Library/Frameworks/Python.framework/Versions/3.7/lib/python3.7/site-packages/django/db/backends/mysql/features.py", line 82, in is_sql_auto_is_null_enabled
cursor.execute('SELECT ##SQL_AUTO_IS_NULL')
File "/Library/Frameworks/Python.framework/Versions/3.7/lib/python3.7/site-packages/django/db/backends/utils.py", line 103, in execute
sql = self.db.ops.last_executed_query(self.cursor, sql, params)
File "/Library/Frameworks/Python.framework/Versions/3.7/lib/python3.7/site-packages/django/db/backends/mysql/operations.py", line 146, in last_executed_query
query = query.decode(errors='replace')
AttributeError: 'str' object has no attribute 'decode'

This is an old issue about previous versions of django. It is currently 3.1.2 and the code block which causes the problem was fixed.
https://github.com/django/django/blob/master/django/db/backends/mysql/operations.py
You may try pip install -U django if your django version is newer then 3.0.0 (good)
Other choices are changing your django versions source code at related line in your virtualenv (ugly), or monkey patch the related function (bad)

How to solve "sqlalchemy.exc.OperationalError" when using Alembic

I want to add columns to a table in my database dynamically since I don't want to have to specify all columns when I set it up in the class
In order to solve this I am instead using alembic to add columns to a table but I am having problems.
In test.py script I have defined a class as below.
DATABASE_URL_dev = "postgresql+psycopg2://user:password#localhost:5432/testdb"
engine = create_engine(DATABASE_URL_dev)
Base = declarative_base(engine)
class my_class1(Base):
__tablename__ = "test1"
id = Column(Integer, primary_key=True)
list = Column(String)
def loadsession():
Base.metadata.create_all(engine)
Session = sessionmaker(bind=engine)
session = Session()
return session
session = loadsession()
Now I want to add a column to table test1 and I am thereby trying to use Alembic.
I followed the instructions at https://alembic.sqlalchemy.org/en/latest/tutorial.html and did the following:
I installed alembic by running pip install alembic
I created an environment using alembic init alembic
In the .ini file I set sqlalchemy.url = "postgresql+psycopg2://user:password#localhost:5432/testdb"
I created a migration script by running alembic revision -m "add a column "
I then edited the script by adding the following "op.add_column('test1', sa.Column('new_column', sa.String))" in upgrade()
I ran the first migration with "alembic upgrade head" This gave me the error: "sqlalchemy.exc.OperationalError: (psycopg2.OperationalError) (Background on this error at: http://sqlalche.me/e/e3q8)"
Question
Have I set sqlalchemy.url correctly or what is else setting the OperationalError?
Entire traceback
Traceback (most recent call last):
File "c:\users\user\appdata\local\programs\python\python38-32\lib\runpy.py", line 193, in _run_module_as_main
return _run_code(code, main_globals, None,
File "c:\users\user\appdata\local\programs\python\python38-32\lib\runpy.py", line 86, in _run_code
exec(code, run_globals)
File "C:\Users\user\AppData\Local\Programs\Python\Python38-32\Scripts\alembic.exe\__main__.py", line 9, in <module>
File "c:\users\user\appdata\local\programs\python\python38-32\lib\site-packages\alembic\config.py", line 577, in main
CommandLine(prog=prog).main(argv=argv)
File "c:\users\user\appdata\local\programs\python\python38-32\lib\site-packages\alembic\config.py", line 571, in main
self.run_cmd(cfg, options)
File "c:\users\user\appdata\local\programs\python\python38-32\lib\site-packages\alembic\config.py", line 548, in run_cmd
fn(
File "c:\users\user\appdata\local\programs\python\python38-32\lib\site-packages\alembic\command.py", line 298, in upgrade
script.run_env()
File "c:\users\user\appdata\local\programs\python\python38-32\lib\site-packages\alembic\script\base.py", line 489, in run_env
util.load_python_file(self.dir, "env.py")
File "c:\users\user\appdata\local\programs\python\python38-32\lib\site-packages\alembic\util\pyfiles.py", line 98, in load_python_file
module = load_module_py(module_id, path)
File "c:\users\user\appdata\local\programs\python\python38-32\lib\site-packages\alembic\util\compat.py", line 184, in load_module_py
spec.loader.exec_module(module)
File "<frozen importlib._bootstrap_external>", line 783, in exec_module
File "<frozen importlib._bootstrap>", line 219, in _call_with_frames_removed
File "y\env.py", line 77, in <module>
run_migrations_online()
File "y\env.py", line 65, in run_migrations_online
with connectable.connect() as connection:
File "c:\users\user\appdata\local\programs\python\python38-32\lib\site-packages\sqlalchemy\engine\base.py", line 2218, in connect
return self._connection_cls(self, **kwargs)
File "c:\users\user\appdata\local\programs\python\python38-32\lib\site-packages\sqlalchemy\engine\base.py", line 103, in __init__
else engine.raw_connection()
File "c:\users\user\appdata\local\programs\python\python38-32\lib\site-packages\sqlalchemy\engine\base.py", line 2317, in raw_connection
return self._wrap_pool_connect(
File "c:\users\user\appdata\local\programs\python\python38-32\lib\site-packages\sqlalchemy\engine\base.py", line 2288, in _wrap_pool_connect
Connection._handle_dbapi_exception_noconnection(
File "c:\users\user\appdata\local\programs\python\python38-32\lib\site-packages\sqlalchemy\engine\base.py", line 1554, in _handle_dbapi_exception_noconnection
util.raise_(
File "c:\users\user\appdata\local\programs\python\python38-32\lib\site-packages\sqlalchemy\util\compat.py", line 178, in raise_
raise exception
File "c:\users\user\appdata\local\programs\python\python38-32\lib\site-packages\sqlalchemy\engine\base.py", line 2285, in _wrap_pool_connect
return fn()
File "c:\users\user\appdata\local\programs\python\python38-32\lib\site-packages\sqlalchemy\pool\base.py", line 303, in unique_connection
return _ConnectionFairy._checkout(self)
File "c:\users\user\appdata\local\programs\python\python38-32\lib\site-packages\sqlalchemy\pool\base.py", line 773, in _checkout
fairy = _ConnectionRecord.checkout(pool)
File "c:\users\user\appdata\local\programs\python\python38-32\lib\site-packages\sqlalchemy\pool\base.py", line 492, in checkout
rec = pool._do_get()
File "c:\users\user\appdata\local\programs\python\python38-32\lib\site-packages\sqlalchemy\pool\impl.py", line 238, in _do_get
return self._create_connection()
File "c:\users\user\appdata\local\programs\python\python38-32\lib\site-packages\sqlalchemy\pool\base.py", line 308, in _create_connection
return _ConnectionRecord(self)
File "c:\users\user\appdata\local\programs\python\python38-32\lib\site-packages\sqlalchemy\pool\base.py", line 437, in __init__
self.__connect(first_connect_check=True)
File "c:\users\user\appdata\local\programs\python\python38-32\lib\site-packages\sqlalchemy\pool\base.py", line 657, in __connect
pool.logger.debug("Error on connect(): %s", e)
File "c:\users\user\appdata\local\programs\python\python38-32\lib\site-packages\sqlalchemy\util\langhelpers.py", line 68, in __exit__
compat.raise_(
File "c:\users\user\appdata\local\programs\python\python38-32\lib\site-packages\sqlalchemy\util\compat.py", line 178, in raise_
raise exception
File "c:\users\user\appdata\local\programs\python\python38-32\lib\site-packages\sqlalchemy\pool\base.py", line 652, in __connect
connection = pool._invoke_creator(self)
File "c:\users\user\appdata\local\programs\python\python38-32\lib\site-packages\sqlalchemy\engine\strategies.py", line 114, in connect
return dialect.connect(*cargs, **cparams)
File "c:\users\user\appdata\local\programs\python\python38-32\lib\site-packages\sqlalchemy\engine\default.py", line 488, in connect
return self.dbapi.connect(*cargs, **cparams)
File "c:\users\c\appdata\local\programs\python\python38-32\lib\site-packages\psycopg2\__init__.py", line 126, in connect
conn = _connect(dsn, connection_factory=connection_factory, **kwasync)
sqlalchemy.exc.OperationalError: (psycopg2.OperationalError)
(Background on this error at: http://sqlalche.me/e/e3q8)

pytest KeyError: 'USER' within docker container

I am in the process of building a docker container that will run my automation tests. When I attempt to run the command below [this works locally and in jenkins] I get the following error:
root#645ed3930434:/test_dir# pytest test_* -m smoke
Traceback (most recent call last):
File "/usr/local/bin/pytest", line 11, in <module>
sys.exit(main())
File "/usr/local/lib/python3.5/dist-packages/_pytest/config.py", line 49, in main
config = _prepareconfig(args, plugins)
File "/usr/local/lib/python3.5/dist-packages/_pytest/config.py", line 168, in _prepareconfig
pluginmanager=pluginmanager, args=args)
File "/usr/local/lib/python3.5/dist-packages/_pytest/vendored_packages/pluggy.py", line 745, in __call__
return self._hookexec(self, self._nonwrappers + self._wrappers, kwargs)
File "/usr/local/lib/python3.5/dist-packages/_pytest/vendored_packages/pluggy.py", line 339, in _hookexec
return self._inner_hookexec(hook, methods, kwargs)
File "/usr/local/lib/python3.5/dist-packages/_pytest/vendored_packages/pluggy.py", line 334, in <lambda>
_MultiCall(methods, kwargs, hook.spec_opts).execute()
File "/usr/local/lib/python3.5/dist-packages/_pytest/vendored_packages/pluggy.py", line 613, in execute
return _wrapped_call(hook_impl.function(*args), self.execute)
File "/usr/local/lib/python3.5/dist-packages/_pytest/vendored_packages/pluggy.py", line 250, in _wrapped_call
wrap_controller.send(call_outcome)
File "/usr/local/lib/python3.5/dist-packages/_pytest/helpconfig.py", line 68, in pytest_cmdline_parse
config = outcome.get_result()
File "/usr/local/lib/python3.5/dist-packages/_pytest/vendored_packages/pluggy.py", line 279, in get_result
raise ex[1].with_traceback(ex[2])
File "/usr/local/lib/python3.5/dist-packages/_pytest/vendored_packages/pluggy.py", line 265, in __init__
self.result = func()
File "/usr/local/lib/python3.5/dist-packages/_pytest/vendored_packages/pluggy.py", line 614, in execute
res = hook_impl.function(*args)
File "/usr/local/lib/python3.5/dist-packages/_pytest/config.py", line 957, in pytest_cmdline_parse
self.parse(args)
File "/usr/local/lib/python3.5/dist-packages/_pytest/config.py", line 1121, in parse
self._preparse(args, addopts=addopts)
File "/usr/local/lib/python3.5/dist-packages/_pytest/config.py", line 1084, in _preparse
self.pluginmanager.load_setuptools_entrypoints('pytest11')
File "/usr/local/lib/python3.5/dist-packages/_pytest/vendored_packages/pluggy.py", line 516, in load_setuptools_entrypoints
self.register(plugin, name=ep.name)
File "/usr/local/lib/python3.5/dist-packages/_pytest/config.py", line 264, in register
ret = super(PytestPluginManager, self).register(plugin, name)
File "/usr/local/lib/python3.5/dist-packages/_pytest/vendored_packages/pluggy.py", line 371, in register
hook._maybe_apply_history(hookimpl)
File "/usr/local/lib/python3.5/dist-packages/_pytest/vendored_packages/pluggy.py", line 768, in _maybe_apply_history
res = self._hookexec(self, [method], kwargs)
File "/usr/local/lib/python3.5/dist-packages/_pytest/vendored_packages/pluggy.py", line 339, in _hookexec
return self._inner_hookexec(hook, methods, kwargs)
File "/usr/local/lib/python3.5/dist-packages/_pytest/vendored_packages/pluggy.py", line 334, in <lambda>
_MultiCall(methods, kwargs, hook.spec_opts).execute()
File "/usr/local/lib/python3.5/dist-packages/_pytest/vendored_packages/pluggy.py", line 614, in execute
res = hook_impl.function(*args)
File "/usr/local/lib/python3.5/dist-packages/pytest_cloud/plugin.py", line 76, in pytest_addoption
os.environ['USER'],
File "/usr/lib/python3.5/os.py", line 725, in __getitem__
raise KeyError(key) from None
KeyError: 'USER'
I am new to docker, so I do not understand what is causing this error.
I am starting with a ubuntu as my base [this also happens when using a https://hub.docker.com/_/python/ as my base]
for reference requirements.txt includes the following:
apipkg==1.4
certifi==2017.11.5
chardet==3.0.4
execnet==1.5.0
idna==2.6
parameterized==0.6.1
psutil==5.4.1
py==1.5.2
pytest==3.2.5
pytest-cloud==2.0.0
pytest-forked==0.2
pytest-xdist==1.20.1
requests==2.18.4
six==1.11.0
timeout-decorator==0.4.0
urllib3==1.22
I have installed Python 3.5.2 in the container

The 'USER' environment variable seems not to defined within your image. Define it externally, or make your code resilient to its absence:
In your code, use os.getenv('USER', backup_user_name) instead of os.environ['USER']
In your code, use getpass instead of relying on your environment to get the current user.
import getpass
print getpass.getuser()
In docker run, you could add -e USER=$(whoami) or something of that sort
In docker-compose, you could add USER: some_user_name under the environ setting for that service.

flask-migrate cannot drop table because other objects depend on it

Problem applying just created migration (Added db.Model) through Flask-Migrate (SQLAlchemy) for PostgresSQL DB.
The error itself:
sqlalchemy.exc.InternalError: (psycopg2.InternalError) cannot drop table parameter_subtype because other objects depend on it
Full error stack trace is:
INFO [alembic.autogenerate.compare] Detected removed foreign key (event_id) (id) on table stage_has_event
INFO [alembic.autogenerate.compare] Detected removed column 'stage_has_event.event_id'
Generating /app/migrations/versions/e224df1a4818_.py ... done
(venv) $ ./manage db upgrade
INFO [alembic.runtime.migration] Context impl PostgresqlImpl.
INFO [alembic.runtime.migration] Will assume transactional DDL.
INFO [alembic.runtime.migration] Running upgrade cadf22871ae0 -> e224df1a4818, empty message
Traceback (most recent call last):
File "/app/venv/bin/flask", line 11, in <module>
sys.exit(main())
File "/app/venv/lib/python2.7/site-packages/flask_cli/cli.py", line 502, in main
cli.main(args=args, prog_name=name)
File "/app/venv/lib/python2.7/site-packages/flask_cli/cli.py", line 369, in main
return AppGroup.main(self, *args, **kwargs)
File "/app/venv/lib/python2.7/site-packages/click/core.py", line 697, in main
rv = self.invoke(ctx)
File "/app/venv/lib/python2.7/site-packages/click/core.py", line 1066, in invoke
return _process_result(sub_ctx.command.invoke(sub_ctx))
File "/app/venv/lib/python2.7/site-packages/click/core.py", line 1066, in invoke
return _process_result(sub_ctx.command.invoke(sub_ctx))
File "/app/venv/lib/python2.7/site-packages/click/core.py", line 895, in invoke
return ctx.invoke(self.callback, **ctx.params)
File "/app/venv/lib/python2.7/site-packages/click/core.py", line 535, in invoke
return callback(*args, **kwargs)
File "/app/venv/lib/python2.7/site-packages/click/decorators.py", line 17, in new_func
return f(get_current_context(), *args, **kwargs)
File "/app/venv/lib/python2.7/site-packages/flask/cli.py", line 257, in decorator
return __ctx.invoke(f, *args, **kwargs)
File "/app/venv/lib/python2.7/site-packages/click/core.py", line 535, in invoke
return callback(*args, **kwargs)
File "/app/venv/lib/python2.7/site-packages/flask_migrate/cli.py", line 134, in upgrade
_upgrade(directory, revision, sql, tag, x_arg)
File "/app/venv/lib/python2.7/site-packages/flask_migrate/__init__.py", line 259, in upgrade
command.upgrade(config, revision, sql=sql, tag=tag)
File "/app/venv/lib/python2.7/site-packages/alembic/command.py", line 254, in upgrade
script.run_env()
File "/app/venv/lib/python2.7/site-packages/alembic/script/base.py", line 427, in run_env
util.load_python_file(self.dir, 'env.py')
File "/app/venv/lib/python2.7/site-packages/alembic/util/pyfiles.py", line 81, in load_python_file
module = load_module_py(module_id, path)
File "/app/venv/lib/python2.7/site-packages/alembic/util/compat.py", line 141, in load_module_py
mod = imp.load_source(module_id, path, fp)
File "migrations/env.py", line 87, in <module>
run_migrations_online()
File "migrations/env.py", line 80, in run_migrations_online
context.run_migrations()
File "<string>", line 8, in run_migrations
File "/app/venv/lib/python2.7/site-packages/alembic/runtime/environment.py", line 836, in run_migrations
self.get_context().run_migrations(**kw)
File "/app/venv/lib/python2.7/site-packages/alembic/runtime/migration.py", line 330, in run_migrations
step.migration_fn(**kw)
File "/app/migrations/versions/e224df1a4818_.py", line 21, in upgrade
op.drop_table('parameter_subtype')
File "<string>", line 8, in drop_table
File "<string>", line 3, in drop_table
File "/app/venv/lib/python2.7/site-packages/alembic/operations/ops.py", line 1187, in drop_table
operations.invoke(op)
File "/app/venv/lib/python2.7/site-packages/alembic/operations/base.py", line 319, in invoke
return fn(self, operation)
File "/app/venv/lib/python2.7/site-packages/alembic/operations/toimpl.py", line 70, in drop_table
operation.to_table(operations.migration_context)
File "/app/venv/lib/python2.7/site-packages/alembic/ddl/impl.py", line 203, in drop_table
self._exec(schema.DropTable(table))
File "/app/venv/lib/python2.7/site-packages/alembic/ddl/impl.py", line 118, in _exec
return conn.execute(construct, *multiparams, **params)
File "/app/venv/lib/python2.7/site-packages/sqlalchemy/engine/base.py", line 948, in execute
return meth(self, multiparams, params)
File "/app/venv/lib/python2.7/site-packages/sqlalchemy/sql/ddl.py", line 68, in _execute_on_connection
return connection._execute_ddl(self, multiparams, params)
File "/app/venv/lib/python2.7/site-packages/sqlalchemy/engine/base.py", line 1009, in _execute_ddl
compiled
File "/app/venv/lib/python2.7/site-packages/sqlalchemy/engine/base.py", line 1200, in _execute_context
context)
File "/app/venv/lib/python2.7/site-packages/sqlalchemy/engine/base.py", line 1413, in _handle_dbapi_exception
exc_info
File "/app/venv/lib/python2.7/site-packages/sqlalchemy/util/compat.py", line 203, in raise_from_cause
reraise(type(exception), exception, tb=exc_tb, cause=cause)
File "/app/venv/lib/python2.7/site-packages/sqlalchemy/engine/base.py", line 1193, in _execute_context
context)
File "/app`enter code here`/venv/lib/python2.7/site-packages/sqlalchemy/engine/default.py", line 507, in do_execute
cursor.execute(statement, parameters)
sqlalchemy.exc.InternalError: (psycopg2.InternalError) cannot drop table parameter_subtype because other objects depend on it
DETAIL: constraint parameter_parameter_subtype_id_fkey on table parameter depends on table parameter_subtype
HINT: Use DROP ... CASCADE to drop the dependent objects too.
[SQL: '\nDROP TABLE parameter_subtype']
This leads to table not created in PostgreSQL db and columns either.
Unsure what may have caused this problem and how to understand this Error message.
I did manually drop the tables and it helped. However how to be with migration.
Any Suggestions?

Flask-Migrate does not read in the database to see the dependencies between the objects. You can achieve a successful migration by reordering the drop_table in your migration file.
What you can do is modify the migration file like so:
op.drop_table("parameter_subtype")
op.drop_table("parameter")
And then run the upgrade command. Normally ordering the drop in this order should solve the problem.

I got the same error and what worked for me was to first drop the table in the database using the command:
$ DROP TABLE table_name;
And then in the migration file in the upgrade() function delete or comment out the line where it says:
op.drop_table('table_name')