clf after defining it; in your case it gives:
DecisionTreeClassifier(ccp_alpha=0.0, class_weight=None, criterion='gini',
max_depth=None, max_features=None, max_leaf_nodes=None,
i.e. all arguments with their default values, since you did not specify anything in the definition
clf = tree.DecisionTreeClassifier().
You can get the parameters of any algorithm in scikit-learn in a similar way.
Tested with scikit-learn v0.22.2
As Ben Reiniger correctly points out in the comment below, from scikit-learn v0.23 onwards, we need to set the display configuration first in order for this to work: