Questions to Chapter 2

Hi Aurelien,

I have some questions concerning the `GridsearchCV` and `RandomsearchCV`. Firstly, concerning the `RandomsearchCV`. what do the `scipy.stats.reciprocal` and `scipy.stats.expon` do exactly?. Why is important to specify an `n_iter` ? what does `n_jobs` do?
secondly, what could be possible reasons for my `Gridsearch` running for a very long while?
Thirdly, what roles do this backend play because i ran my `Gridsearch` with `C` having values of up to 300,000 and i had an error concerning the backend. How could this be solved?
1)The code below just keeps running :

```python
processed = full_pipeline.fit_transform(practice_set)

#training model
from sklearn.svm import SVR
from sklearn.metrics import mean_squared_error
from sklearn.model_selection import cross_val_score
from sklearn.model_selection import GridSearchCV
svm_reg = SVR(gamma='auto')
predictor = svm_reg.fit(processed,practice_set_labels)
predictions = svm_reg.predict(processed)
mean_squared_error = mean_squared_error(y_true=practice_set_labels,y_pred=predictions)
rmse = np.sqrt(mean_squared_error)

#cross validation
#score = cross_val_score(svm_reg,processed,practice_set_labels,scoring='neg_mean_squared_error',cv=10)
#cv_score = np.sqrt(-score)

def display(score):
print('scores\n',score)
print(score.mean())
print(score.std())
params = [{'kernel':['linear','rbf'],'C':[1.,3.,30.,100.]}]
grid_search = GridSearchCV(svm_reg,param_grid=params,scoring='neg_mean_squared_error',cv=5)
grid_search.fit(processed,practice_set_labels)
print(grid_search.best_score_)
```

2)Running this one which is identical to that of the Jupyter notebook:

```python
processed = full_pipeline.fit_transform(practice_set)

#training model
from sklearn.svm import SVR
from sklearn.metrics import mean_squared_error
from sklearn.model_selection import cross_val_score
from sklearn.model_selection import GridSearchCV
svm_reg = SVR(gamma='auto')
predictor = svm_reg.fit(processed,practice_set_labels)
predictions = svm_reg.predict(processed)
mean_squared_error = mean_squared_error(y_true=practice_set_labels,y_pred=predictions)
rmse = np.sqrt(mean_squared_error)

#cross validation
#score = cross_val_score(svm_reg,processed,practice_set_labels,scoring='neg_mean_squared_error',cv=10)
#cv_score = np.sqrt(-score)

def display(score):
print('scores\n',score)
print(score.mean())
print(score.std())

param_grid = [
{'kernel': ['linear'], 'C': [10., 30., 100., 300., 1000., 3000., 10000., 30000.0]},
{'kernel': ['rbf'], 'C': [1.0, 3.0, 10., 30., 100., 300., 1000.0],
'gamma': [0.01, 0.03, 0.1, 0.3, 1.0, 3.0]},
]

svm_reg = SVR()
grid_search = GridSearchCV(svm_reg, param_grid, cv=5, scoring='neg_mean_squared_error', verbose=2, n_jobs=4)
grid_search.fit(processed, practice_set_labels)
```

ERROR MESSAGE:

```
[Parallel(n_jobs=4)]: Using backend LokyBackend with 4 concurrent workers.
exception calling callback for
joblib.externals.loky.process_executor._RemoteTraceback:
'''
Traceback (most recent call last):
File "C:\Users\fritz\AppData\Local\Programs\Python\Python37\lib\multiprocessing\queues.py", line 109, in get
self._sem.release()
OSError: [WinError 6] Das Handle ist ungültig

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
File "C:\Users\fritz\Hello\lib\site-packages\joblib\externals\loky\process_executor.py", line 391, in _process_worker
call_item = call_queue.get(block=True, timeout=timeout)
File "C:\Users\fritz\AppData\Local\Programs\Python\Python37\lib\multiprocessing\queues.py", line 111, in get
self._rlock.release()
OSError: [WinError 6] Das Handle ist ungültig
'''

The above exception was the direct cause of the following exception:

Traceback (most recent call last):
File "C:\Users\fritz\Hello\lib\site-packages\joblib\externals\loky\_base.py", line 625, in _invoke_callbacks
callback(self)
File "C:\Users\fritz\Hello\lib\site-packages\joblib\parallel.py", line 309, in __call__
self.parallel.dispatch_next()
File "C:\Users\fritz\Hello\lib\site-packages\joblib\parallel.py", line 731, in dispatch_next
if not self.dispatch_one_batch(self._original_iterator):
File "C:\Users\fritz\Hello\lib\site-packages\joblib\parallel.py", line 759, in dispatch_one_batch
self._dispatch(tasks)
File "C:\Users\fritz\Hello\lib\site-packages\joblib\parallel.py", line 716, in _dispatch
job = self._backend.apply_async(batch, callback=cb)
File "C:\Users\fritz\Hello\lib\site-packages\joblib\_parallel_backends.py", line 510, in apply_async
future = self._workers.submit(SafeFunction(func))
File "C:\Users\fritz\Hello\lib\site-packages\joblib\externals\loky\reusable_executor.py", line 151, in submit
fn, *args, **kwargs)
File "C:\Users\fritz\Hello\lib\site-packages\joblib\externals\loky\process_executor.py", line 1022, in submit
raise self._flags.broken
joblib.externals.loky.process_executor.BrokenProcessPool: A task has failed to un-serialize. Please ensure that the arguments of the function are all picklable.
FEHLER: Der Prozess "37772" wurde nicht gefunden.
FEHLER: Der Prozess "32116" wurde nicht gefunden.
FEHLER: Der Prozess "37652" wurde nicht gefunden.
FEHLER: Der Prozess "7540" wurde nicht gefunden.
joblib.externals.loky.process_executor._RemoteTraceback:
'''
Traceback (most recent call last):
File "C:\Users\fritz\AppData\Local\Programs\Python\Python37\lib\multiprocessing\queues.py", line 109, in get
self._sem.release()
OSError: [WinError 6] Das Handle ist ungültig

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
File "C:\Users\fritz\Hello\lib\site-packages\joblib\externals\loky\process_executor.py", line 391, in _process_worker
call_item = call_queue.get(block=True, timeout=timeout)
File "C:\Users\fritz\AppData\Local\Programs\Python\Python37\lib\multiprocessing\queues.py", line 111, in get
self._rlock.release()
OSError: [WinError 6] Das Handle ist ungültig
'''

The above exception was the direct cause of the following exception:

Traceback (most recent call last):
File "C:/Users/fritz/PycharmProjects/Hello/Chap-2_Excercise.py", line 110, in
grid_search.fit(processed, practice_set_labels)
File "C:\Users\fritz\Hello\lib\site-packages\sklearn\model_selection\_search.py", line 688, in fit
self._run_search(evaluate_candidates)
File "C:\Users\fritz\Hello\lib\site-packages\sklearn\model_selection\_search.py", line 1149, in _run_search
evaluate_candidates(ParameterGrid(self.param_grid))
File "C:\Users\fritz\Hello\lib\site-packages\sklearn\model_selection\_search.py", line 667, in evaluate_candidates
cv.split(X, y, groups)))
File "C:\Users\fritz\Hello\lib\site-packages\joblib\parallel.py", line 934, in __call__
self.retrieve()
File "C:\Users\fritz\Hello\lib\site-packages\joblib\parallel.py", line 833, in retrieve
self._output.extend(job.get(timeout=self.timeout))
File "C:\Users\fritz\Hello\lib\site-packages\joblib\_parallel_backends.py", line 521, in wrap_future_result
return future.result(timeout=timeout)
File "C:\Users\fritz\AppData\Local\Programs\Python\Python37\lib\concurrent\futures\_base.py", line 432, in result
return self.__get_result()
File "C:\Users\fritz\AppData\Local\Programs\Python\Python37\lib\concurrent\futures\_base.py", line 384, in __get_result
raise self._exception
File "C:\Users\fritz\Hello\lib\site-packages\joblib\externals\loky\_base.py", line 625, in _invoke_callbacks
callback(self)
File "C:\Users\fritz\Hello\lib\site-packages\joblib\parallel.py", line 309, in __call__
self.parallel.dispatch_next()
File "C:\Users\fritz\Hello\lib\site-packages\joblib\parallel.py", line 731, in dispatch_next
if not self.dispatch_one_batch(self._original_iterator):
File "C:\Users\fritz\Hello\lib\site-packages\joblib\parallel.py", line 759, in dispatch_one_batch
self._dispatch(tasks)
File "C:\Users\fritz\Hello\lib\site-packages\joblib\parallel.py", line 716, in _dispatch
job = self._backend.apply_async(batch, callback=cb)
File "C:\Users\fritz\Hello\lib\site-packages\joblib\_parallel_backends.py", line 510, in apply_async
future = self._workers.submit(SafeFunction(func))
File "C:\Users\fritz\Hello\lib\site-packages\joblib\externals\loky\reusable_executor.py", line 151, in submit
fn, *args, **kwargs)
File "C:\Users\fritz\Hello\lib\site-packages\joblib\externals\loky\process_executor.py", line 1022, in submit
raise self._flags.broken
joblib.externals.loky.process_executor.BrokenProcessPool: A task has failed to un-serialize. Please ensure that the arguments of the function are all picklable.

Process finished with exit code 1
```