input: Write a python function to calculate the percentage of vowels in a given text.
  assert vowel_percentage("Hello World!") == 30.0
  assert vowel_percentage("Python") == 16.666666666666664
  assert vowel_percentage("AEIOUaeiou") == 100.0
  assert vowel_percentage("bcdfg") == 0.0
output: def vowel_percentage(text):
      vowels = "aeiouAEIOU"
      total_chars = len(text)
      vowel_count = sum(1 for char in text if char in vowels)
      return (vowel_count / total_chars) * 100 if total_chars > 0 else 0.0