[CodeLlama]: simplify infilling with <FILL_ME> (huggingface#1424)

* CodeLlama: simplify infilling with `<FILL_ME>`.

Co-authored-by: Arthur <[email protected]>

* Use `AutoTokenizer`

It now works after [these PRs](https://huggingface.co/codellama/CodeLlama-7b-hf/discussions/11) have been merged.

---------

Co-authored-by: Arthur <[email protected]>

codellama.md

@@ -151,7 +151,7 @@ This is a specialized task particular to code models. The model is trained to ge
 
 This task is available in the **base** and **instruction** variants of the 7B and 13B models. It is _not_ available for any of the 34B models or the Python versions.
 
-To use this feature successfully, you need to pay close attention to the format used to train the model for this task, as it uses special separators to identify the different parts of the prompt. Let's see an example:
+To use this feature successfully, you need to pay close attention to the format used to train the model for this task, as it uses special separators to identify the different parts of the prompt. Fortunately, transformers' `CodeLlamaTokenizer` makes this very easy, as demonstrated below:
 
 ```python
 from transformers import AutoTokenizer, AutoModelForCausalLM
@@ -165,38 +165,40 @@ model = AutoModelForCausalLM.from_pretrained(
     torch_dtype=torch.float16
 ).to("cuda")
 
-prefix = 'def remove_non_ascii(s: str) -> str:\n    """ '
-suffix = "\n    return result\n"
-
-prompt = f"<PRE> {prefix} <SUF>{suffix} <MID>"
-inputs = tokenizer(prompt, return_tensors="pt").to("cuda")
+prompt = '''def remove_non_ascii(s: str) -> str:
+    """ <FILL_ME>
+    return result
+'''
 
+input_ids = tokenizer(prompt, return_tensors="pt")["input_ids"].to("cuda")
 output = model.generate(
-    inputs["input_ids"],
+    input_ids,
     max_new_tokens=200,
-    do_sample=False,
 )
 output = output[0].to("cpu")
-print(tokenizer.decode(output))
-```
 
+filling = tokenizer.decode(output[input_ids.shape[1]:], skip_special_tokens=True)
+print(prompt.replace("<FILL_ME>", filling))
 ```
-<s> <PRE> def remove_non_ascii(s: str) -> str:
-    """ <SUF>
-    return result
- <MID>
-    Remove non-ASCII characters from a string.
 
-    :param s: The string to remove non-ASCII characters from.
-    :return: The string with non-ASCII characters removed.
+```Python
+def remove_non_ascii(s: str) -> str:
+    """ Remove non-ASCII characters from a string.
+
+    Args:
+        s: The string to remove non-ASCII characters from.
+
+    Returns:
+        The string with non-ASCII characters removed.
     """
     result = ""
     for c in s:
         if ord(c) < 128:
-            result += c <EOT></s>
+            result += c
+    return result
 ```
 
-In order to use the completion, you’ll need to process the output to cut the text between the `<MID>` and `<EOT>` tokens – that’s what goes between the prefix and suffix we supplied.
+Under the hood, the tokenizer [automatically splits by `<FILL_ME>`](https://huggingface.co/docs/transformers/main/model_doc/code_llama#transformers.CodeLlamaTokenizer.fill_token) to create a formatted input string that follows [the original training pattern](https://github.com/facebookresearch/codellama/blob/cb51c14ec761370ba2e2bc351374a79265d0465e/llama/generation.py#L402). This is more robust than preparing the pattern yourself: it avoids pitfalls, such as token glueing, that are very hard to debug.
 
 #### Conversational Instructions