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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def make_graph(values, lower_limit=0.0, upper_limit=100.0, style="blocks"):
 """ Draws a graph made of unicode characters. :param values: An array of values to graph. :param lower_limit: Minimum value for the y axis (or None for dynamic). :param upper_limit: Maximum value for the y axis (or None for dynamic). :param style: Drawing style ('blocks', 'braille-fill', 'braille-peak', or 'braille-snake'). :returns: Bar as a string """


    values = [float(n) for n in values]
    mn, mx = min(values), max(values)
    mn = mn if lower_limit is None else min(mn, float(lower_limit))
    mx = mx if upper_limit is None else max(mx, float(upper_limit))
    extent = mx - mn

    if style == 'blocks':
        bar = '_▁▂▃▄▅▆▇█'
        bar_count = len(bar) - 1
        if extent == 0:
            graph = '_' * len(values)
        else:
            graph = ''.join(bar[int((n - mn) / extent * bar_count)] for n in values)
    elif style in ['braille-fill', 'braille-peak', 'braille-snake']:
        # idea from https://github.com/asciimoo/drawille
        # unicode values from http://en.wikipedia.org/wiki/Braille

        vpad = values if len(values) % 2 == 0 else values + [mn]
        vscale = [round(4 * (vp - mn) / extent) for vp in vpad]
        l = len(vscale) // 2

        # do the 2-character collapse separately for clarity
        if 'fill' in style:
            vbits = [[0, 0x40, 0x44, 0x46, 0x47][vs] for vs in vscale]
        elif 'peak' in style:
            vbits = [[0, 0x40, 0x04, 0x02, 0x01][vs] for vs in vscale]
        else:
            assert('snake' in style)
            # there are a few choices for what to put last in vb2.
            # arguable vscale[-1] from the _previous_ call is best.
            vb2 = [vscale[0]] + vscale + [0]
            vbits = []
            for i in range(1, l + 1):
                c = 0
                for j in range(min(vb2[i - 1], vb2[i], vb2[i + 1]), vb2[i] + 1):
                    c |= [0, 0x40, 0x04, 0x02, 0x01][j]
                vbits.append(c)

        # 2-character collapse
        graph = ''
        for i in range(0, l, 2):
            b1 = vbits[i]
            b2 = vbits[i + 1]
            if b2 & 0x40:
                b2 = b2 - 0x30
            b2 = b2 << 3
            graph += chr(0x2800 + b1 + b2)
    else:
        raise NotImplementedError("Graph drawing style '%s' unimplemented." % style)
    return graph