Helper that transforms TF-graph generating function into a regular one.
        See `_resize` function below.

def _tffunc(*argtypes):
        '''Helper that transforms TF-graph generating function into a regular one.
        See `_resize` function below.
        '''
        placeholders = list(map(tf.placeholder, argtypes))
        def wrap(f):
            out = f(*placeholders)
            def wrapper(*args, **kw):
                return out.eval(dict(zip(placeholders, args)), session=kw.get('session'))
            return wrapper
        return wrap