Detect string width on screen

east_asian_width.py

import unicodedata

# https://www.unicode.org/reports/tr11/tr11-14.html
EAW_WIDTH = {
  'F': 2,   # Full-width
  'H': 1,   # Half-width
  'W': 2,   # Wide
  'Na': 1,  # Narrow
  'A': 2,   # Ambiguous
  'N': 1    # Not East Asian (Neutral)
}

def _letter_width(c):
  eaw = unicodedata.east_asian_width(c)
  return EAW_WIDTH[eaw]

def string_width(s):
  width = 0
  for c in s:
    width += _letter_width(c)
  return width

def _padding_width(s, width):
  w = string_width(s)
  ret = width - w
  if ret > 0:
    return ret
  else:
    return 0

def rpad(s, width):
  w = _padding_width(s, width)
  return s + " " * w

def lpad(s, width):
  w = _padding_width(s, width)
  return " " * w + s

ljust=rpad
rjust=lpad

if __name__ == "__main__":
  import unittest

  class Test(unittest.TestCase):
    def test_letter_width(self):
      self.assertEqual(_letter_width("c"), 1)
      self.assertEqual(_letter_width("あ"), 2)
      self.assertEqual(_letter_width("ｱ"), 1)
      self.assertEqual(string_width("cあｱ"), 4)
      self.assertEqual(_padding_width("cあｱ", 10), 6)
      self.assertEqual(_padding_width("cあｱ", 2), 0)
      self.assertEqual(rpad("cあｱ", 10), "cあｱ      ")
      self.assertEqual(rpad("cあｱ", 2), "cあｱ")
      self.assertEqual(lpad("cあｱ", 10), "      cあｱ")
      self.assertEqual(lpad("cあｱ", 2), "cあｱ")
      self.assertEqual(ljust("cあｱ", 10), "cあｱ      ")
      self.assertEqual(ljust("cあｱ", 2), "cあｱ")
      self.assertEqual(rjust("cあｱ", 10), "      cあｱ")
      self.assertEqual(rjust("cあｱ", 2), "cあｱ")

  unittest.main()