suggest_uniform throws error using MySQL

Conditions

• Optuna version:0.10.0
• Python version:3.7.3
• OS:Ubuntu 16.04.6

Using MySQL, when reloading a study and optimizing over n_trials>1, an error occurs when optuna processes the suggest_uniform command.

Code to reproduce

import optuna
import numpy as np

def run(trial):

    variable = trial.suggest_uniform(name='Var', low=0, high=1)
    loss = np.random.rand()

    return loss

study = optuna.create_study(study_name="bugReproduce",
                            storage='mysql+pymysql://login:password@host/BugReport',
                            load_if_exists=True)

study.optimize(run, n_trials=10)

Error messages, stack traces, or logs

The first time around everything runs fine

[I 2019-05-07 10:48:58,797] A new study created with name: bugReproduce
[I 2019-05-07 10:48:58,863] Finished trial#0 resulted in value: 0.04761668417531628. Current best value is 0.0476167 with parameters: {'Int': 1, 'Categorical': True, 'Var': 0.190561}.
[I 2019-05-07 10:48:58,916] Finished trial#1 resulted in value: 0.8832107587679441. Current best value is 0.0476167 with parameters: {'Int': 1, 'Categorical': True, 'Var': 0.190561}.
[I 2019-05-07 10:48:58,968] Finished trial#2 resulted in value: 0.7393299144453355. Current best value is 0.0476167 with parameters: {'Int': 1, 'Categorical': True, 'Var': 0.190561}.
[I 2019-05-07 10:48:59,022] Finished trial#3 resulted in value: 0.29801114852614885. Current best value is 0.0476167 with parameters: {'Int': 1, 'Categorical': True, 'Var': 0.190561}.
[I 2019-05-07 10:48:59,074] Finished trial#4 resulted in value: 0.6454763494664104. Current best value is 0.0476167 with parameters: {'Int': 1, 'Categorical': True, 'Var': 0.190561}.
[I 2019-05-07 10:48:59,126] Finished trial#5 resulted in value: 0.5779246647098616. Current best value is 0.0476167 with parameters: {'Int': 1, 'Categorical': True, 'Var': 0.190561}.
[I 2019-05-07 10:48:59,179] Finished trial#6 resulted in value: 0.7350985202999127. Current best value is 0.0476167 with parameters: {'Int': 1, 'Categorical': True, 'Var': 0.190561}.
[I 2019-05-07 10:48:59,231] Finished trial#7 resulted in value: 0.46640685007041527. Current best value is 0.0476167 with parameters: {'Int': 1, 'Categorical': True, 'Var': 0.190561}.
[I 2019-05-07 10:48:59,284] Finished trial#8 resulted in value: 0.9331917753402831. Current best value is 0.0476167 with parameters: {'Int': 1, 'Categorical': True, 'Var': 0.190561}.
[I 2019-05-07 10:48:59,337] Finished trial#9 resulted in value: 0.5997692796594932. Current best value is 0.0476167 with parameters: {'Int': 1, 'Categorical': True, 'Var': 0.190561}.

The second time though the following AttributeError is thrown:

[I 2019-05-07 10:49:00,922] Using an existing study with name 'bugReproduce' instead of creating a new one.
[W 2019-05-07 10:49:00,978] Setting status of trial#10 as TrialState.FAIL because of the following error: AttributeError("'numpy.float64' object has no attribute 'translate'")
Traceback (most recent call last):
  File "/home/dbi/merlin/anaconda3/envs/GQA2/lib/python3.7/site-packages/optuna/study.py", line 399, in _run_trial
    result = func(trial)
  File "bug1.py", line 10, in run
    variable = trial.suggest_uniform(name='Var', low=0, high=1)
  File "/home/dbi/merlin/anaconda3/envs/GQA2/lib/python3.7/site-packages/optuna/trial.py", line 151, in suggest_uniform
    return self._suggest(name, distributions.UniformDistribution(low=low, high=high))
  File "/home/dbi/merlin/anaconda3/envs/GQA2/lib/python3.7/site-packages/optuna/trial.py", line 413, in _suggest
    param_value_in_internal_repr, distribution)
  File "/home/dbi/merlin/anaconda3/envs/GQA2/lib/python3.7/site-packages/optuna/storages/rdb/storage.py", line 369, in set_trial_param
    commit_success = self._commit_with_integrity_check(session)
  File "/home/dbi/merlin/anaconda3/envs/GQA2/lib/python3.7/site-packages/optuna/storages/rdb/storage.py", line 624, in _commit_with_integrity_check
    session.commit()
  File "/home/dbi/merlin/anaconda3/envs/GQA2/lib/python3.7/site-packages/sqlalchemy/orm/session.py", line 1026, in commit
    self.transaction.commit()
  File "/home/dbi/merlin/anaconda3/envs/GQA2/lib/python3.7/site-packages/sqlalchemy/orm/session.py", line 493, in commit
    self._prepare_impl()
  File "/home/dbi/merlin/anaconda3/envs/GQA2/lib/python3.7/site-packages/sqlalchemy/orm/session.py", line 472, in _prepare_impl
    self.session.flush()
  File "/home/dbi/merlin/anaconda3/envs/GQA2/lib/python3.7/site-packages/sqlalchemy/orm/session.py", line 2451, in flush
    self._flush(objects)
  File "/home/dbi/merlin/anaconda3/envs/GQA2/lib/python3.7/site-packages/sqlalchemy/orm/session.py", line 2589, in _flush
    transaction.rollback(_capture_exception=True)
  File "/home/dbi/merlin/anaconda3/envs/GQA2/lib/python3.7/site-packages/sqlalchemy/util/langhelpers.py", line 68, in __exit__
    compat.reraise(exc_type, exc_value, exc_tb)
  File "/home/dbi/merlin/anaconda3/envs/GQA2/lib/python3.7/site-packages/sqlalchemy/util/compat.py", line 129, in reraise
    raise value
  File "/home/dbi/merlin/anaconda3/envs/GQA2/lib/python3.7/site-packages/sqlalchemy/orm/session.py", line 2549, in _flush
    flush_context.execute()
  File "/home/dbi/merlin/anaconda3/envs/GQA2/lib/python3.7/site-packages/sqlalchemy/orm/unitofwork.py", line 422, in execute
    rec.execute(self)
  File "/home/dbi/merlin/anaconda3/envs/GQA2/lib/python3.7/site-packages/sqlalchemy/orm/unitofwork.py", line 589, in execute
    uow,
  File "/home/dbi/merlin/anaconda3/envs/GQA2/lib/python3.7/site-packages/sqlalchemy/orm/persistence.py", line 245, in save_obj
    insert,
  File "/home/dbi/merlin/anaconda3/envs/GQA2/lib/python3.7/site-packages/sqlalchemy/orm/persistence.py", line 1120, in _emit_insert_statements
    statement, params
  File "/home/dbi/merlin/anaconda3/envs/GQA2/lib/python3.7/site-packages/sqlalchemy/engine/base.py", line 988, in execute
    return meth(self, multiparams, params)
  File "/home/dbi/merlin/anaconda3/envs/GQA2/lib/python3.7/site-packages/sqlalchemy/sql/elements.py", line 287, in _execute_on_connection
    return connection._execute_clauseelement(self, multiparams, params)
  File "/home/dbi/merlin/anaconda3/envs/GQA2/lib/python3.7/site-packages/sqlalchemy/engine/base.py", line 1107, in _execute_clauseelement
    distilled_params,
  File "/home/dbi/merlin/anaconda3/envs/GQA2/lib/python3.7/site-packages/sqlalchemy/engine/base.py", line 1248, in _execute_context
    e, statement, parameters, cursor, context
  File "/home/dbi/merlin/anaconda3/envs/GQA2/lib/python3.7/site-packages/sqlalchemy/engine/base.py", line 1468, in _handle_dbapi_exception
    util.reraise(*exc_info)
  File "/home/dbi/merlin/anaconda3/envs/GQA2/lib/python3.7/site-packages/sqlalchemy/util/compat.py", line 129, in reraise
    raise value
  File "/home/dbi/merlin/anaconda3/envs/GQA2/lib/python3.7/site-packages/sqlalchemy/engine/base.py", line 1244, in _execute_context
    cursor, statement, parameters, context
  File "/home/dbi/merlin/anaconda3/envs/GQA2/lib/python3.7/site-packages/sqlalchemy/engine/default.py", line 552, in do_execute
    cursor.execute(statement, parameters)
  File "/home/dbi/merlin/anaconda3/envs/GQA2/lib/python3.7/site-packages/pymysql/cursors.py", line 168, in execute
    query = self.mogrify(query, args)
  File "/home/dbi/merlin/anaconda3/envs/GQA2/lib/python3.7/site-packages/pymysql/cursors.py", line 147, in mogrify
    query = query % self._escape_args(args, conn)
  File "/home/dbi/merlin/anaconda3/envs/GQA2/lib/python3.7/site-packages/pymysql/cursors.py", line 127, in _escape_args
    return {key: conn.literal(val) for (key, val) in args.items()}
  File "/home/dbi/merlin/anaconda3/envs/GQA2/lib/python3.7/site-packages/pymysql/cursors.py", line 127, in <dictcomp>
    return {key: conn.literal(val) for (key, val) in args.items()}
  File "/home/dbi/merlin/anaconda3/envs/GQA2/lib/python3.7/site-packages/pymysql/connections.py", line 467, in literal
    return self.escape(obj, self.encoders)
  File "/home/dbi/merlin/anaconda3/envs/GQA2/lib/python3.7/site-packages/pymysql/connections.py", line 460, in escape
    return converters.escape_item(obj, self.charset, mapping=mapping)
  File "/home/dbi/merlin/anaconda3/envs/GQA2/lib/python3.7/site-packages/pymysql/converters.py", line 27, in escape_item
    val = encoder(val, mapping)
  File "/home/dbi/merlin/anaconda3/envs/GQA2/lib/python3.7/site-packages/pymysql/converters.py", line 118, in escape_unicode
    return u"'%s'" % _escape_unicode(value)
  File "/home/dbi/merlin/anaconda3/envs/GQA2/lib/python3.7/site-packages/pymysql/converters.py", line 73, in _escape_unicode
    return value.translate(_escape_table)
AttributeError: 'numpy.float64' object has no attribute 'translate'

This occurs when choosing a sufficiently high number of trials. Setting n_trials=10 has consistently allowed me to reproduce the error.

[MerlinDumeur]

@toshihikoyanase Thank you for the advice! mysqlconnector seems to work on my environment as well.

@sile Thanks for the suggestion. I tend to avoid working with unreleased libraries as they tend to be unstable, however it might prove useful in case there are no alternatives.

[sile]

FYI

@MerlinDumeur As another workaround different from the above, you can install the latest (unreleased) Optuna via pip install git+https://github.com/pfnet/optuna.git command.