Add utils.deprecation_warning

Summary: Pull Request resolved: https://github.com/pytorch/fairseq/pull/607

Differential Revision: D14681031

Pulled By: myleott

fbshipit-source-id: 466ee526a30543218e2b7138fb651db866ae5ab3

fairseq/utils.py

@@ -12,6 +12,7 @@ import os
 import re
 import sys
 import traceback
+import warnings
 
 import torch
 import torch.nn.functional as F
@@ -463,3 +464,8 @@ def log_softmax(x, dim, onnx_trace=False):
         return F.log_softmax(x.float(), dim=dim)
     else:
         return F.log_softmax(x, dim=dim, dtype=torch.float32)
+
+
+def deprecation_warning(message, stacklevel=3):
+    # don't use DeprecationWarning, since it's ignored by default
+    warnings.warn(message, stacklevel=stacklevel)