1 files changed, 85 insertions, 0 deletions
diff --git a/text_recognizer/data/sentence_generator.py b/text_recognizer/data/sentence_generator.py
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+++ b/text_recognizer/data/sentence_generator.py
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+"""Downloading the Brown corpus with NLTK for sentence generating."""
+
+import itertools
+import re
+import string
+from typing import Optional
+
+import nltk
+from nltk.corpus.reader.util import ConcatenatedCorpusView
+import numpy as np
+
+from text_recognizer.datasets.util import DATA_DIRNAME
+
+NLTK_DATA_DIRNAME = DATA_DIRNAME / "downloaded" / "nltk"
+
+
+class SentenceGenerator:
+    """Generates text sentences using the Brown corpus."""
+
+    def __init__(self, max_length: Optional[int] = None) -> None:
+        """Loads the corpus and sets word start indices."""
+        self.corpus = brown_corpus()
+        self.word_start_indices = [0] + [
+            _.start(0) + 1 for _ in re.finditer(" ", self.corpus)
+        ]
+        self.max_length = max_length
+
+    def generate(self, max_length: Optional[int] = None) -> str:
+        """Generates a word or sentences from the Brown corpus.
+
+        Sample a string from the Brown corpus of length at least one word and at most max_length, padding to
+        max_length with the '_' characters if sentence is shorter.
+
+        Args:
+            max_length (Optional[int]): The maximum number of characters in the sentence. Defaults to None.
+
+        Returns:
+            str: A sentence from the Brown corpus.
+
+        Raises:
+            ValueError: If max_length was not specified at initialization and not given as an argument.
+
+        """
+        if max_length is None:
+            max_length = self.max_length
+        if max_length is None:
+            raise ValueError(
+                "Must provide max_length to this method or when making this object."
+            )
+        
+        for _ in range(10):
+            try:
+                index = np.random.randint(0, len(self.word_start_indices) - 1)
+                start_index = self.word_start_indices[index]
+                end_index_candidates = []
+                for index in range(index + 1, len(self.word_start_indices)):
+                    if self.word_start_indices[index] - start_index > max_length:
+                        break
+                    end_index_candidates.append(self.word_start_indices[index])
+                end_index = np.random.choice(end_index_candidates)
+                sampled_text = self.corpus[start_index:end_index].strip()
+                return sampled_text
+            except Exception:
+                pass
+        raise RuntimeError("Was not able to generate a valid string")
+
+
+def brown_corpus() -> str:
+    """Returns a single string with the Brown corpus with all punctuations stripped."""
+    sentences = load_nltk_brown_corpus()
+    corpus = " ".join(itertools.chain.from_iterable(sentences))
+    corpus = corpus.translate({ord(c): None for c in string.punctuation})
+    corpus = re.sub(" +", " ", corpus)
+    return corpus
+
+
+def load_nltk_brown_corpus() -> ConcatenatedCorpusView:
+    """Load the Brown corpus using the NLTK library."""
+    nltk.data.path.append(NLTK_DATA_DIRNAME)
+    try:
+        nltk.corpus.brown.sents()
+    except LookupError:
+        NLTK_DATA_DIRNAME.mkdir(parents=True, exist_ok=True)
+        nltk.download("brown", download_dir=NLTK_DATA_DIRNAME)
+    return nltk.corpus.brown.sents()