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# PLBart

## Overview

The PLBART model was proposed in [Unified Pre-training for Program Understanding and Generation](https://arxiv.org/abs/2103.06333) by Wasi Uddin Ahmad, Saikat Chakraborty, Baishakhi Ray, Kai-Wei Chang.
This is a BART-like model which can be used to perform code-summarization, code-generation, and code-translation tasks. The pre-trained model `plbart-base` has been trained using multilingual denoising task
on Java, Python and English.

According to the abstract

*Code summarization and generation empower conversion between programming language (PL) and natural language (NL),
while code translation avails the migration of legacy code from one PL to another. This paper introduces PLBART, 
a sequence-to-sequence model capable of performing a broad spectrum of program and language understanding and generation tasks.
PLBART is pre-trained on an extensive collection of Java and Python functions and associated NL text via denoising autoencoding.
Experiments on code summarization in the English language, code generation, and code translation in seven programming languages
show that PLBART outperforms or rivals state-of-the-art models. Moreover, experiments on discriminative tasks, e.g., program
repair, clone detection, and vulnerable code detection, demonstrate PLBART's effectiveness in program understanding.
Furthermore, analysis reveals that PLBART learns program syntax, style (e.g., identifier naming convention), logical flow
(e.g., if block inside an else block is equivalent to else if block) that are crucial to program semantics and thus excels
even with limited annotations.*

This model was contributed by [gchhablani](https://huggingface.co/gchhablani). The Authors' code can be found [here](https://github.com/wasiahmad/PLBART).

## Usage examples

PLBart is a multilingual encoder-decoder (sequence-to-sequence) model primarily intended for code-to-text, text-to-code, code-to-code tasks. As the
model is multilingual it expects the sequences in a different format. A special language id token is added in both the
source and target text. The source text format is `X [eos, src_lang_code]` where `X` is the source text. The
target text format is `[tgt_lang_code] X [eos]`. `bos` is never used.

However, for fine-tuning, in some cases no language token is provided in cases where a single language is used. Please refer to [the paper](https://arxiv.org/abs/2103.06333) to learn more about this.

In cases where the language code is needed, the regular [`~PLBartTokenizer.__call__`] will encode source text format 
when you pass texts as the first argument or with the keyword argument `text`, and will encode target text format if
it's passed with the `text_target` keyword argument.

### Supervised training

```python
>>> from transformers import PLBartForConditionalGeneration, PLBartTokenizer

>>> tokenizer = PLBartTokenizer.from_pretrained("uclanlp/plbart-base", src_lang="en_XX", tgt_lang="python")
>>> example_python_phrase = "def maximum(a,b,c):NEW_LINE_INDENTreturn max([a,b,c])"
>>> expected_translation_english = "Returns the maximum value of a b c."
>>> inputs = tokenizer(example_python_phrase, text_target=expected_translation_english, return_tensors="pt")
>>> model(**inputs)
```

### Generation

  While generating the target text set the `decoder_start_token_id` to the target language id. The following
  example shows how to translate Python to English using the `uclanlp/plbart-python-en_XX` model.

```python
>>> from transformers import PLBartForConditionalGeneration, PLBartTokenizer

>>> tokenizer = PLBartTokenizer.from_pretrained("uclanlp/plbart-python-en_XX", src_lang="python", tgt_lang="en_XX")
>>> example_python_phrase = "def maximum(a,b,c):NEW_LINE_INDENTreturn max([a,b,c])"
>>> inputs = tokenizer(example_python_phrase, return_tensors="pt")
>>> model = PLBartForConditionalGeneration.from_pretrained("uclanlp/plbart-python-en_XX")
>>> translated_tokens = model.generate(**inputs, decoder_start_token_id=tokenizer.lang_code_to_id["en_XX"])
>>> tokenizer.batch_decode(translated_tokens, skip_special_tokens=True)[0]
"Returns the maximum value of a b c."
```

## Resources

- [Text classification task guide](../tasks/sequence_classification)
- [Causal language modeling task guide](../tasks/language_modeling)
- [Translation task guide](../tasks/translation)
- [Summarization task guide](../tasks/summarization)

## PLBartConfig

[[autodoc]] PLBartConfig

## PLBartTokenizer

[[autodoc]] PLBartTokenizer
    - build_inputs_with_special_tokens

## PLBartModel

[[autodoc]] PLBartModel
    - forward

## PLBartForConditionalGeneration

[[autodoc]] PLBartForConditionalGeneration
    - forward

## PLBartForSequenceClassification

[[autodoc]] PLBartForSequenceClassification
    - forward

## PLBartForCausalLM

[[autodoc]] PLBartForCausalLM
    - forward