add friendly error msg to py_reader (#18316)

python/paddle/fluid/layers/io.py

@@ -28,6 +28,7 @@ from ..framework import convert_np_dtype_to_dtype_, default_main_program, \
     default_startup_program, program_guard, Program, Variable
 from ..layer_helper import LayerHelper
 from ..unique_name import generate as unique_name
+import logging
 
 __all__ = [
     'data', 'open_files', 'read_file', 'shuffle', 'batch', 'double_buffer',
@@ -593,6 +594,7 @@ def _py_reader(capacity,
                 feed_queue.close()
             except Exception as ex:
                 feed_queue.close()
+                logging.warn('Your decorated reader has raised an exception!')
                 raise ex
 
         reader.thread = threading.Thread(target=__provider_thread__)

python/paddle/fluid/reader.py

@@ -23,6 +23,7 @@ from .executor import global_scope
 from .data_feeder import DataFeeder, BatchedTensorProvider, ListTensorProvider
 from .layers.io import monkey_patch_reader_methods, _copy_reader_var_, double_buffer
 from .unique_name import UniqueNameGenerator
+import logging
 
 __all__ = ['PyReader']
 
@@ -441,6 +442,7 @@ class PyReader(object):
                 self._queue.close()
             except Exception as ex:
                 self._queue.close()
+                logging.warn('Your decorated reader has raised an exception!')
                 raise ex
 
         self._thread = threading.Thread(target=__thread_main__)