frequency.py

def english_test(bytes_):
    # From http://www.data-compression.com/english.html
    freqs = {
        'a': 0.0651738,
        'b': 0.0124248,
        'c': 0.0217339,
        'd': 0.0349835,
        'e': 0.1041442,
        'f': 0.0197881,
        'g': 0.0158610,
        'h': 0.0492888,
        'i': 0.0558094,
        'j': 0.0009033,
        'k': 0.0050529,
        'l': 0.0331490,
        'm': 0.0202124,
        'n': 0.0564513,
        'o': 0.0596302,
        'p': 0.0137645,
        'q': 0.0008606,
        'r': 0.0497563,
        's': 0.0515760,
        't': 0.0729357,
        'u': 0.0225134,
        'v': 0.0082903,
        'w': 0.0171272,
        'x': 0.0013692,
        'y': 0.0145984,
        'z': 0.0007836,
        ' ': 0.1918182
    }

    try:
        msg = bytes_.decode('ascii').lower()
    except:
        return 0

    filtered = list(filter(lambda c: c in freqs.keys(), msg))
    if not filtered:
        return 0

    error = 0
    for c, ratio in freqs.items():
        actual = filtered.count(c) / len(filtered)
        error += abs(ratio - actual)

    return 1 / error