Keras 2, TypeError: can't pickle _thread.lock objects

Question

I am using Keras to create an ANN and do a grid search on the network. I have encountered the following error while running the code below:

model = KerasClassifier(build_fn=create_model(input_dim), verbose=0)
# define the grid search parameters
batch_size = [10, 20]
epochs = [50, 100]
dropout = [0.3, 0.5, 0.7]
param_grid = dict(dropout_rate=dropout, batch_size=batch_size, nb_epoch=epochs)
pipe.append(('classify', model))
params.append(param_grid)
pipeline=Pipeline(pipe)
#the pipeline also contains feature selector, but for convenience I do not include code here
piped_classifier =  GridSearchCV(estimator=pipeline, param_grid=params, n_jobs=-1,
                        cv=nfold)
piped_classifier.fit(X_train, y_train) #this is line 246 of classifier_gridsearch.py causing error, see below,


def create_model(input_dim,dropout_rate=0.0):
    # create model
    model = Sequential()
    model.add(Dense(80,
                    input_dim=input_dim,
                    kernel_initializer='uniform', activation='relu'))
    model.add(Dropout(dropout_rate))
    model.add(Dense(1, kernel_initializer='uniform', activation='sigmoid'))
    # Compile model
    model.compile(loss='binary_crossentropy', optimizer='adam', metrics=['accuracy'])
    return model

The error of line 246 throws an error as below, with a long stacktrace:

Traceback (most recent call last):
  File "/home/zqz/Work/chase/python/src/exp/classifier_gridsearch_main.py", line 176, in <module>
    classifier.gridsearch()
  File "/home/zqz/Work/chase/python/src/exp/classifier_gridsearch_main.py", line 155, in gridsearch
    self.fs_option,self.fs_gridsearch)
  File "/home/zqz/Work/chase/python/src/ml/classifier_gridsearch.py", line 246, in learn_dnn
    piped_classifier.fit(X_train, y_train)
  File "/home/zqz/Programs/anaconda3/lib/python3.6/site-packages/sklearn/model_selection/_search.py", line 945, in fit
    return self._fit(X, y, groups, ParameterGrid(self.param_grid))
  File "/home/zqz/Programs/anaconda3/lib/python3.6/site-packages/sklearn/model_selection/_search.py", line 550, in _fit
    base_estimator = clone(self.estimator)
  File "/home/zqz/Programs/anaconda3/lib/python3.6/site-packages/sklearn/base.py", line 69, in clone
    new_object_params[name] = clone(param, safe=False)
  File "/home/zqz/Programs/anaconda3/lib/python3.6/site-packages/sklearn/base.py", line 57, in clone
    return estimator_type([clone(e, safe=safe) for e in estimator])
  File "/home/zqz/Programs/anaconda3/lib/python3.6/site-packages/sklearn/base.py", line 57, in <listcomp>
    return estimator_type([clone(e, safe=safe) for e in estimator])
  File "/home/zqz/Programs/anaconda3/lib/python3.6/site-packages/sklearn/base.py", line 57, in clone
    return estimator_type([clone(e, safe=safe) for e in estimator])
  File "/home/zqz/Programs/anaconda3/lib/python3.6/site-packages/sklearn/base.py", line 57, in <listcomp>
    return estimator_type([clone(e, safe=safe) for e in estimator])
  File "/home/zqz/Programs/anaconda3/lib/python3.6/site-packages/sklearn/base.py", line 69, in clone
    new_object_params[name] = clone(param, safe=False)
  File "/home/zqz/Programs/anaconda3/lib/python3.6/site-packages/sklearn/base.py", line 60, in clone
    return copy.deepcopy(estimator)
  File "/home/zqz/Programs/anaconda3/lib/python3.6/copy.py", line 180, in deepcopy
    y = _reconstruct(x, memo, *rv)
  File "/home/zqz/Programs/anaconda3/lib/python3.6/copy.py", line 280, in _reconstruct
    state = deepcopy(state, memo)
  File "/home/zqz/Programs/anaconda3/lib/python3.6/copy.py", line 150, in deepcopy
    y = copier(x, memo)
  File "/home/zqz/Programs/anaconda3/lib/python3.6/copy.py", line 240, in _deepcopy_dict
    y[deepcopy(key, memo)] = deepcopy(value, memo)
  File "/home/zqz/Programs/anaconda3/lib/python3.6/copy.py", line 150, in deepcopy
    y = copier(x, memo)
  File "/home/zqz/Programs/anaconda3/lib/python3.6/copy.py", line 215, in _deepcopy_list
    append(deepcopy(a, memo))
  File "/home/zqz/Programs/anaconda3/lib/python3.6/copy.py", line 180, in deepcopy
    y = _reconstruct(x, memo, *rv)
  File "/home/zqz/Programs/anaconda3/lib/python3.6/copy.py", line 280, in _reconstruct
    state = deepcopy(state, memo)
  File "/home/zqz/Programs/anaconda3/lib/python3.6/copy.py", line 150, in deepcopy
    y = copier(x, memo)
  File "/home/zqz/Programs/anaconda3/lib/python3.6/copy.py", line 240, in _deepcopy_dict
    y[deepcopy(key, memo)] = deepcopy(value, memo)
  File "/home/zqz/Programs/anaconda3/lib/python3.6/copy.py", line 150, in deepcopy
    y = copier(x, memo)
  File "/home/zqz/Programs/anaconda3/lib/python3.6/copy.py", line 215, in _deepcopy_list
    append(deepcopy(a, memo))
  File "/home/zqz/Programs/anaconda3/lib/python3.6/copy.py", line 180, in deepcopy
    y = _reconstruct(x, memo, *rv)
  File "/home/zqz/Programs/anaconda3/lib/python3.6/copy.py", line 280, in _reconstruct
    state = deepcopy(state, memo)
  File "/home/zqz/Programs/anaconda3/lib/python3.6/copy.py", line 150, in deepcopy
    y = copier(x, memo)
  File "/home/zqz/Programs/anaconda3/lib/python3.6/copy.py", line 240, in _deepcopy_dict
    y[deepcopy(key, memo)] = deepcopy(value, memo)
  File "/home/zqz/Programs/anaconda3/lib/python3.6/copy.py", line 180, in deepcopy
    y = _reconstruct(x, memo, *rv)
  File "/home/zqz/Programs/anaconda3/lib/python3.6/copy.py", line 280, in _reconstruct
    state = deepcopy(state, memo)
  File "/home/zqz/Programs/anaconda3/lib/python3.6/copy.py", line 150, in deepcopy
    y = copier(x, memo)
  File "/home/zqz/Programs/anaconda3/lib/python3.6/copy.py", line 240, in _deepcopy_dict
    y[deepcopy(key, memo)] = deepcopy(value, memo)
  File "/home/zqz/Programs/anaconda3/lib/python3.6/copy.py", line 180, in deepcopy
    y = _reconstruct(x, memo, *rv)
  File "/home/zqz/Programs/anaconda3/lib/python3.6/copy.py", line 280, in _reconstruct
    state = deepcopy(state, memo)
  File "/home/zqz/Programs/anaconda3/lib/python3.6/copy.py", line 150, in deepcopy
    y = copier(x, memo)
  File "/home/zqz/Programs/anaconda3/lib/python3.6/copy.py", line 240, in _deepcopy_dict
    y[deepcopy(key, memo)] = deepcopy(value, memo)
  File "/home/zqz/Programs/anaconda3/lib/python3.6/copy.py", line 180, in deepcopy
    y = _reconstruct(x, memo, *rv)
  File "/home/zqz/Programs/anaconda3/lib/python3.6/copy.py", line 280, in _reconstruct
    state = deepcopy(state, memo)
  File "/home/zqz/Programs/anaconda3/lib/python3.6/copy.py", line 150, in deepcopy
    y = copier(x, memo)
  File "/home/zqz/Programs/anaconda3/lib/python3.6/copy.py", line 240, in _deepcopy_dict
    y[deepcopy(key, memo)] = deepcopy(value, memo)
  File "/home/zqz/Programs/anaconda3/lib/python3.6/copy.py", line 169, in deepcopy
    rv = reductor(4)
TypeError: can't pickle _thread.lock objects

Any suggestions how to fix this please, thanks

Answer 1

OK the problem seems to be passing method as an argument, in this line:

model = KerasClassifier(build_fn=create_model(input_dim), verbose=0)

create_model is the argument to be passed to build_fn, but I wanted to pass another argument to create_model. But this is not the right way of doing it and hence causing the error.

The error message is not informative in this case, unfortunately.