Add per-label thresholds

[yosipk]

Closes #2274

[yosipk]

This could be more robust, i.e. this particular line would break if user sets an integer as multi_label_threshold.

[yosipk]

Also, doing this only in constructor means if the multi_label_threshold is set from somewhere else (e.g. from reading state dict), it would still be float rather than a dict.

[yosipk]

If the multi_label_threshold does not have key default this fails. This should be checked anywhere where self.multi_label_threshold is set (in constructor, when saving or loading the model?)

[yosipk]

Possibility is to have multi_label_threshold as a property, and check for this stuff in setter. Example code:

class Model:

    def __init__(self, threshold):
        self.threshold = threshold

    @property
    def threshold(self):
        return self._threshold

    @threshold.setter
    def threshold(self, x):
        if type(x) is not dict:
            raise Exception('Not a dict')
        elif 'default' not in x:
            raise Exception('default key not present')
        else:
            self._threshold = x

[yosipk]

Consider checking if x is a number, e.g.

from numbers import Number
...
if type(x) is dict:
  ...
elif isinstance(x, Number):
  self._multi_label_threshold = {'default': x}
else:
  raise Exception('The multi_label_threshold should be either a dict or a number') 

[alanakbik]

@yosipk thanks for adding this - very helpful!