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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def check_cv(cv, X=None, y=None, classifier=False):
 """Input checker utility for building a CV in a user friendly way. Parameters cv : int, a cv generator instance, or None The input specifying which cv generator to use. It can be an integer, in which case it is the number of folds in a KFold, None, in which case 3 fold is used, or another object, that will then be used as a cv generator. X : array-like The data the cross-val object will be applied on. y : array-like The target variable for a supervised learning problem. classifier : boolean optional Whether the task is a classification task, in which case stratified KFold will be used. Returns ------- checked_cv: a cross-validation generator instance. The return value is guaranteed to be a cv generator instance, whatever the input type. """

    return _check_cv(cv, X=X, y=y, classifier=classifier, warn_mask=True)