#!/usr/bin/env python3 -u
# Copyright (c) Facebook, Inc. and its affiliates.
#
# This source code is licensed under the MIT license found in the
# LICENSE file in the root directory of this source tree.
"""
Evaluate the perplexity of a trained language model.
"""
import numpy as np
import torch
from fairseq import checkpoint_utils, options, progress_bar, tasks, utils
from fairseq.data import LMContextWindowDataset
from fairseq.meters import StopwatchMeter, TimeMeter
from fairseq.sequence_scorer import SequenceScorer
class WordStat(object):
def __init__(self, word, is_bpe):
self.word = word
self.is_bpe = is_bpe
self.log_prob = 0
self.next_word_prob = 0
self.count = 0
self.missing_next_words = 0
def add(self, log_prob, next_word_prob):
""" increments counters for the sum of log probs of current word and next
word (given context ending at current word). Since the next word might be at the end of the example,
or it might be not counted because it is not an ending subword unit,
also keeps track of how many of those we have seen """
if next_word_prob is not None:
self.next_word_prob += next_word_prob
else:
self.missing_next_words += 1
self.log_prob += log_prob
self.count += 1
def __str__(self):
return '{}\t{}\t{}\t{}\t{}\t{}'.format(self.word, self.count, self.log_prob, self.is_bpe,
self.next_word_prob, self.count - self.missing_next_words)
def main(parsed_args):
assert parsed_args.path is not None, '--path required for evaluation!'
utils.import_user_module(parsed_args)
print(parsed_args)
use_cuda = torch.cuda.is_available() and not parsed_args.cpu
task = tasks.setup_task(parsed_args)
# Load ensemble
print('| loading model(s) from {}'.format(parsed_args.path))
models, args = checkpoint_utils.load_model_ensemble(
parsed_args.path.split(':'),
arg_overrides=eval(parsed_args.model_overrides),
task=task,
)
for arg in vars(parsed_args).keys():
if arg not in {
'self_target', 'future_target', 'past_target', 'tokens_per_sample',
'output_size_dictionary', 'add_bos_token',
}:
setattr(args, arg, getattr(parsed_args, arg))
# reduce tokens per sample by the required context window size
args.tokens_per_sample -= args.context_window
task = tasks.setup_task(args)
# Load dataset splits
task.load_dataset(args.gen_subset)
dataset = task.dataset(args.gen_subset)
if args.context_window > 0:
dataset = LMContextWindowDataset(
dataset=dataset,
tokens_per_sample=args.tokens_per_sample,
context_window=args.context_window,
pad_idx=task.source_dictionary.pad(),
)
print('| {} {} {} examples'.format(args.data, args.gen_subset, len(dataset)))
# Optimize ensemble for generation and set the source and dest dicts on the model (required by scorer)
for model in models:
model.make_generation_fast_()
if args.fp16:
model.half()
if use_cuda:
model.cuda()
assert len(models) > 0
print('num. model params: {}'.format(sum(p.numel() for p in models[0].parameters())))
itr = task.get_batch_iterator(
dataset=dataset,
max_tokens=args.max_tokens or 36000,
max_sentences=args.max_sentences,
max_positions=utils.resolve_max_positions(*[
model.max_positions() for model in models
]),
ignore_invalid_inputs=True,
num_shards=args.num_shards,
shard_id=args.shard_id,
num_workers=args.num_workers,
).next_epoch_itr(shuffle=False)
gen_timer = StopwatchMeter()
scorer = SequenceScorer(task.target_dictionary, args.softmax_batch)
score_sum = 0.
count = 0
if args.remove_bpe is not None:
if args.remove_bpe == 'sentencepiece':
raise NotImplementedError
else:
bpe_cont = args.remove_bpe.rstrip()
bpe_toks = set(
i
for i in range(len(task.source_dictionary))
if task.source_dictionary[i].endswith(bpe_cont)
)
bpe_len = len(bpe_cont)
else:
bpe_toks = None
bpe_len = 0
word_stats = dict()
with progress_bar.build_progress_bar(args, itr) as t:
wps_meter = TimeMeter()
for sample in t:
if 'net_input' not in sample:
continue
sample = utils.move_to_cuda(sample) if use_cuda else sample
gen_timer.start()
hypos = scorer.generate(models, sample)
gen_timer.stop(sample['ntokens'])
for i, hypos_i in enumerate(hypos):
hypo = hypos_i[0]
sample_id = sample['id'][i]
tokens = hypo['tokens']
tgt_len = tokens.numel()
pos_scores = hypo['positional_scores'].float()
if args.add_bos_token:
assert hypo['tokens'][0].item() == task.target_dictionary.bos()
tokens = tokens[1:]
pos_scores = pos_scores[1:]
skipped_toks = 0
if bpe_toks is not None:
for i in range(tgt_len - 1):
if tokens[i].item() in bpe_toks:
skipped_toks += 1
pos_scores[i + 1] += pos_scores[i]
pos_scores[i] = 0
inf_scores = pos_scores.eq(float('inf')) | pos_scores.eq(float('-inf'))
if inf_scores.any():
print('| Skipping tokens with inf scores:',
task.target_dictionary.string(tokens[inf_scores.nonzero()]))
pos_scores = pos_scores[(~inf_scores).nonzero()]
score_sum += pos_scores.sum().cpu()
count += pos_scores.numel() - skipped_toks
if args.output_word_probs or args.output_word_stats:
w = ''
word_prob = []
is_bpe = False
for i in range(len(tokens)):
w_ind = tokens[i].item()
w += task.source_dictionary[w_ind]
if bpe_toks is not None and w_ind in bpe_toks:
w = w[:-bpe_len]
is_bpe = True
else:
word_prob.append((w, pos_scores[i].item()))
next_prob = None
ind = i + 1
while ind < len(tokens):
if pos_scores[ind].item() != 0:
next_prob = pos_scores[ind]
break
ind += 1
word_stats.setdefault(w, WordStat(w, is_bpe)).add(pos_scores[i].item(), next_prob)
is_bpe = False
w = ''
if args.output_word_probs:
print(
str(int(sample_id)) + " "
+ ('\t'.join('{} [{:2f}]'.format(x[0], x[1]) for x in word_prob))
)
wps_meter.update(sample['ntokens'])
t.log({'wps': round(wps_meter.avg)})
avg_nll_loss = -score_sum / count
print('| Evaluated {} tokens in {:.1f}s ({:.2f} tokens/s)'.format(gen_timer.n, gen_timer.sum, 1. / gen_timer.avg))
print('| Loss: {:.4f}, Perplexity: {:.2f}'.format(avg_nll_loss, np.exp(avg_nll_loss)))
if args.output_word_stats:
for ws in sorted(word_stats.values(), key=lambda x: x.count, reverse=True):
print(ws)
def cli_main():
parser = options.get_eval_lm_parser()
args = options.parse_args_and_arch(parser)
main(args)
if __name__ == '__main__':
cli_main()