code: def _validate_loss_input(loss):
      dir_f = dir(F)
      loss_fns = [d.lower() for d in dir_f]
      if isinstance(loss, str):
          if loss.lower() == "unconstrained":
              return lambda x: x
          elif loss.lower() == "unconstrained_sum":
              return lambda x: x.sum()
          elif loss.lower() == "unconstrained_mean":
              return lambda x: x.mean()
          else:
              try:
                  str_idx = loss_fns.index(loss.lower())
              except:
                  raise ValueError(
                      "Invalid loss string input - must match pytorch function."
                  )
              return getattr(F, dir(F)[str_idx])
      elif callable(loss):
          return loss
      else:
          raise ValueError("Invalid loss input")
  
file_path: pywick/pywick/modules/_utils.py
imports: import datetime
  import warnings
  import torch.nn.functional
  import torch.optim
  from ..metrics import Metric, CategoricalAccuracy, BinaryAccuracy
  from ..initializers import GeneralInitializer
label_desc: Use image node_id 6 for calling a global function with example usage: _validate_loss_input(loss) and returns: function, loss, function, function, getattr