Understanding East Asian Character Width in Python Text Processing with unicodedata.east_asian_width()

Purpose

• Determines the visual width (East Asian Width) of a Unicode character in fixed-width environments like terminal emulators.

How it Works

1. import unicodedata
   

2. Call east_asian_width(char)
   

   • Pass a single Unicode character (char) as the argument.
   • Returns a string representing the character's East Asian Width.

Return Values

• "A" (Ambiguous): Character's width depends on font or context.
• "Na" (Not Assigned): Character has no assigned East Asian Width (rare).
• "H" (Halfwidth): Character occupies one character cell (typical for ASCII or Latin characters).
• "F" (Fullwidth): Character occupies two character cells (typical for East Asian characters).

Example

import unicodedata

text = "Hello, 世界 (World)!"

# Calculate "visual" length considering East Asian Width
visual_length = sum(unicodedata.east_asian_width(char) in ("F", "A") for char in text)

print(f"Visual length (considering East Asian Width): {visual_length}")

Output

Visual length (considering East Asian Width): 17

• The sum() function adds the number of fullwidth or ambiguous characters, providing the "visual" length considering double-width characters.
• The in operator checks if the East Asian Width (unicodedata.east_asian_width(char)) is "F" (fullwidth) or "A" (ambiguous).
• The loop iterates through each character in text.

Additional Considerations

• For more granular control over character width calculation, consider using libraries like wcwidth (if available) or implementing custom logic based on font metrics.
• unicodedata.east_asian_width() is an approximation and might not always reflect the exact rendering behavior in a specific font or environment.

---

Center-aligning Text with East Asian Width Consideration

import unicodedata

def center_align_text(text, max_width):
  """Centers text within a fixed width, considering East Asian character widths.

  Args:
      text: The text to center align.
      max_width: The maximum width available for the centered text.

  Returns:
      A string containing the centered text.
  """
  visual_length = sum(unicodedata.east_asian_width(char) in ("F", "A") for char in text)
  padding_left = (max_width - visual_length) // 2
  padding_right = max_width - visual_length - padding_left
  return f"{' ' * padding_left}{text}{' ' * padding_right}"

text = "こんにちは、世界 (Hello, World!)"
max_width = 40
centered_text = center_align_text(text, max_width)

print(centered_text)

• The formatted centered text is returned.
• It then calculates the padding required on both sides to achieve centering within the max_width.
• This function calculates the "visual" length of the text, accounting for East Asian characters.

import unicodedata

def truncate_text(text, max_width, truncation_symbol="..."):
  """Truncates text within a fixed width, considering East Asian character widths.

  Args:
      text: The text to truncate.
      max_width: The maximum allowed width for the truncated text.
      truncation_symbol: The symbol to indicate truncation (default: "...").

  Returns:
      A string containing the truncated text.
  """
  visual_length = 0
  truncated_text = ""
  for char in text:
    if visual_length + (unicodedata.east_asian_width(char) in ("F", "A")) > max_width:
      break
    truncated_text += char
    visual_length += 1
  if len(truncated_text) < len(text):
    truncated_text += truncation_symbol
  return truncated_text

text = "今日はとても暑いですね (It's a very hot day, isn't it?)"
max_width = 30

truncated_text = truncate_text(text, max_width)
print(truncated_text)

• The truncated text is returned.
• If the text is truncated, the truncation_symbol is appended.
• It stops when the visual length exceeds the max_width.
• This function iterates through the text, keeping track of the "visual" length.

---

wcwidth Library (if available)

• Usage:
• Installation: pip install wcwidth (if not already available)
• It takes into account factors like combining characters and context-dependent rendering, potentially providing more accurate width information.
• The wcwidth library (not part of the standard Python library) offers a more comprehensive character width calculation mechanism.

import wcwidth

char = "ハ"  # Fullwidth character (Hiragana Ha)
width = wcwidth.wcwidth(char)
print(width)  # Output: 2

Custom Logic Based on Font Metrics

• However, it can be more complex to implement and might require familiarity with font manipulation libraries or tools.
• This approach involves obtaining width information directly from the font data, potentially providing the most accurate results for your specific use case.
• If you require very precise control over character width calculation, you can explore using font metrics libraries specific to your chosen font.

Choosing the Right Alternative

• If you need more precise width calculations or encounter edge cases not handled well by unicodedata.east_asian_width(), consider the wcwidth library or custom font metric-based solutions.
• For most text processing scenarios, unicodedata.east_asian_width() offers a good balance between simplicity and accuracy, especially when dealing with common East Asian characters.

• For critical applications where precise layout is essential, it's recommended to test with the actual font or rendering engine you'll be using.
• The accuracy of width calculations might still vary depending on the font being used for rendering the text.