[CTRL] warn if generation prompt does not start with a control code

see also https://github.com/salesforce/ctrl/pull/50

examples/README.md

@@ -101,7 +101,7 @@ python run_lm_finetuning.py \
 
 Based on the script [`run_generation.py`](https://github.com/huggingface/transformers/blob/master/examples/run_generation.py).
 
-Conditional text generation using the auto-regressive models of the library: GPT, GPT-2, Transformer-XL and XLNet.
+Conditional text generation using the auto-regressive models of the library: GPT, GPT-2, Transformer-XL, XLNet, CTRL.
 A similar script is used for our official demo [Write With Transfomer](https://transformer.huggingface.co), where you
 can try out the different models available in the library.
 

examples/run_generation.py

@@ -196,7 +196,7 @@ def main():
 
     logger.info(args)
     if args.model_type in ["ctrl"]:
-        if args.temperature > 0.7 : 
+        if args.temperature > 0.7:
             logger.info('CTRL typically works better with lower temperatures (and lower top_k).')
 
     while True:
@@ -224,6 +224,9 @@ def main():
             # Models with memory likes to have a long prompt for short inputs.
             raw_text = (args.padding_text if args.padding_text else PADDING_TEXT) + raw_text
         context_tokens = tokenizer.encode(raw_text)
+        if args.model_type == "ctrl":
+            if not any(context_tokens[0] == x for x in tokenizer.control_codes.values()):
+                logger.info("WARNING! You are not starting your generation from a control code so you won't get good results")
         out = sample_sequence(
             model=model,
             context=context_tokens,