ensure that all attributes with trailing underscore in fit are leared after the entire logic has succeded

[solegalli]

All attributes with trailing underscore must be set up at the end of the fit() functionality, when we are sure that all fit logic worked. At the moment, it is not like that for all transformers.

Add a test like the one in test_encoders:

@pytest.mark.parametrize("estimator", _estimators)
def test_raises_non_fitted_error_when_error_during_fit(estimator):
    X, y = test_df(categorical=True)
    X.loc[len(X) - 1] = nan
    transformer = clone(estimator)

    with pytest.raises(ValueError):
        transformer.fit(X, y)

    # Test when fit is not called prior to transform.
    with pytest.raises(NotFittedError):
        transformer.transform(X)

Modules encoding and preprocessing already have this functionality.

Modules to update:

• imputation
• encoding
• discretisation
• outliers
• transformation
• scaling
• creation
• datetime
• text
• selection
• time series
• preproc
• wrappers

Related PRs:

• [ENH] defer trailing underscore attribute assignment in fit() for imputers and discretisers #917

[direkkakkar319-ops]

Hi, @solegalli , I looked into the issue and found that we can fix it by moving all underscore attribute assignments to the end of fit(), after all logic succeeds:
for example:-

def fit(self, X, y=None):
    variables_ = find_variables(X)     
    self._check_na(X, variables_)
    encoder_dict_ = {}
    # ... rest of logic ...
    self.variables_ = variables_  
    self.encoder_dict_ = encoder_dict_

[direkkakkar319-ops]

hi, @solegalli , this PR closes #586 , all the 15 checks have passed including the 2 codcov checks, looking forward for a review and would appreciate your feedback

[direkkakkar319-ops]

Happy to make any changes you suggest