Music note to its frequency

frequency.py

import re

def frequency(note):
    aFreqs = {
        -1: 13.75,
        0: 27.5,
        1: 55.0,
        2: 110.0,
        3: 220.0,
        4: 440.0,
        5: 880.0,
        6: 1760.0,
        7: 3520.0,
        8: 7040.0, 
    }
    sharpable = ['A', 'C', 'D', 'F', 'G']
    step = 2 ** (1.0 / 12)

    pattern = re.compile(r'([A-G])(#|b)?([0-8])')
    match = pattern.match(note)
    
    if match is None:
        return -1

    letter, modifier, number = match.group(1, 2, 3)
    number = int(number)

    if 'C' <= letter and letter <= 'G':
        number -= 1

    currentFreq = aFreqs[number]
    currentLetter = 'A'
    isSharped = False
    while currentLetter != letter:
        currentFreq *= step
        if not isSharped and currentLetter in sharpable:
            isSharped = True
        else:
            currentLetter = chr(ord(currentLetter) + 1)
            isSharped = False

    if modifier == '#':
        return currentFreq * step
    elif modifier == 'b':
        return currentFreq / step
    else:
        return currentFreq