Problem

A common interview question that I’ve seen goes as follows:

Write a function to crop a text corpus without breaking any word.

  • Take the length of the text up to which character you should trim.
  • Make sure that the cropped text doesn’t have any trailing space.
  • Try to maximize the number of words you can pack in your trimmed text.

Your function should look something like this:

def crop(text: str, limit: int) -> str:
    """Crops 'text' upto 'limit' characters."""

    # Crop the text.
    cropped_text = perform_crop()
    return cropped_text

For example, if text looks like this—

"A quick brown fox jumps over the lazy dog."

and you’re asked to crop it up to 9 characters, then the function crop should return:

"A quick"

and not:

"A quick "

or:

"A quick b"

Solution

This is quite easily solvable by using Python’s textwrap.shorten function. The shorten function takes quite a few parameters1. However, we’ll only need the following ones to do our job:

  • text: str: Target text that we’re going to operate on.
  • width: int : Desired width after cropping.
  • initial_indent: str: Character to use for the initial indentation. Provide empty string for no initial indentation.
  • subsequent_indent: str: Character to use for the subsequent indentation. Provide empty string for no subsequent indentation.
  • break_long_words: bool: Whether to break long words or not.
  • break_on_hyphens: bool: Whether to break words on hyphens or not.
  • placeholder: bool: Placeholder character. The default here is [...]. However, provide an empty string if you don’t want any placeholder after the cropped string. The length of the placeholder is going to be included in the total length of the cropped text.

With the descriptions out of the way, let’s write the crop function here:

# src.py
import textwrap


def crop(text: str, limit: int) -> str:
    cropped_text = textwrap.shorten(
        text,
        width=limit,
        initial_indent="",
        subsequent_indent="",
        break_long_words=False,
        break_on_hyphens=False,
        placeholder="",
    )
    return cropped_text


if __name__ == "__main__":
    cropped_text = crop(
        text="A quick brown fox jumps over the lazy dog.",
        limit=9,
    )

    print(cropped_text)

This prints out the desired output as follows:

A quick

You can see that we achieved our goal of cropping a text corpus without breaking any word. Try playing around with the initial_indent, subsequent_indent, and placeholder parameters and see how they change the output.

Complete solution with tests

# src.py
import textwrap
import unittest


def crop(text: str, limit: int) -> str:
    cropped_text = textwrap.shorten(
        text,
        width=limit,
        initial_indent="",
        subsequent_indent="",
        break_long_words=False,
        break_on_hyphens=False,
        placeholder="",
    )
    return cropped_text


class TestCrop(unittest.TestCase):
    def setUp(self):
        self.text = "This is an example of speech synthesis in English."
        self.text_complex = """
        wrap(), fill() and shorten() work by creating a TextWrapper instance
        and calling a single method on it.
        """

    def test_ok(self):
        cropped_text = crop(self.text, limit=10)
        self.assertEqual(cropped_text, "This is an")

    def test_complex_ok(self):
        cropped_text = crop(self.text_complex, limit=15)
        self.assertEqual(cropped_text, "wrap(), fill()")

    def test_no_word_break(self):
        cropped_text = crop(self.text, limit=9)
        self.assertNotEqual(cropped_text, "This is a")

    def test_no_trailing_space(self):
        cropped_text = crop(self.text, limit=8)
        self.assertNotEqual(cropped_text, "This is ")


if __name__ == "__main__":
    unittest.main()

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