That function expects decimal for s (saturation) and v (value), not percent. Divide by 100.

>>> import colorsys

# Using percent, incorrect
>>> test_color = colorsys.hsv_to_rgb(359,100,100)
>>> test_color
(100, -9900.0, -9900.0)

# Using decimal, correct
>>> test_color = colorsys.hsv_to_rgb(1,1,1)
>>> test_color
(1, 0.0, 0.0)

If you would like the non-normalized RGB tuple, here is a function to wrap the colorsys function.

def hsv2rgb(h,s,v):
    return tuple(round(i * 255) for i in colorsys.hsv_to_rgb(h,s,v))

Example functionality

>>> hsv2rgb(0.5,0.5,0.5)
(64, 128, 128)

RGB is here a 3-tuple, but you can not pass this tuple to color_rgb: this method requires three parameters. You can however unpack the tuple in three parameters, with for example the asterisk (*) in front:

pt.setFill(color_rgb(*RGB))

or you can first unpack the tuple in three variables:

r, g, b = RGB
pt.setFill(color_rgb(r, g, b))

Note however that if the v parameter is set to 0, this will always return (0, 0, 0) since HSV is basically a cone, and the v parameter determines the distance from the "top" to the "surface", as is demonstrated on the Wikipedia image [wiki] below:

So with v=0, this will always result in black, regardless of the value for the hue and saturation.

Try using colorsys:

import colorsys
colorsys.hsv_to_rgb(0.5, 0.5, 0.4)

Output:

(0.2, 0.4, 0.4)

An example could be:

import matplotlib
import matplotlib.pyplot as plt
import colorsys

h, s, v = 0.83, 1.0, 0.50
# RGB values are from 0 to 1, NOT from 0 to 255
r, g, b = colorsys.hsv_to_rgb(h, s, v)
print(r, g, b)

rect1 = matplotlib.patches.Rectangle((-200, -100), 400, 200, color=[r, g, b])
plt.axes().add_patch(rect1)
plt.show()

To see why you may be having troubles in displaying color using imshow, refer to: Printing one color using imshow

The RGB values in Blender use a linear color model while the Hex values use gamma corrected non-linear color model.

To convert between these two, you would have to manually do the gamma calculations using the transfer function of your color profile, wich is set in the Color Management section of your Scene – set to sRGB by default.

The excact conversion is listed in the sRGB Wikipedia article.

def linear_to_srgb(r, g, b):
    def linear(c):
        a = .055
        if c <= .0031308:
            return 12.92 * c
        else:
            return (1+a) * c**(1/2.4) - a
    return tuple(linear(c) for c in (r, g, b))

def srgb_to_linear(r, g, b):
    def srgb(c):
        a = .055
        if c <= .04045:
            return c / 12.92
        else:
            return ((c+a) / (1+a)) ** 2.4
    return tuple(srgb(c) for c in (r, g, b))

import colorsys
col = colorsys.hsv_to_rgb(.4, .8, 1)
# (0.19999999999999996, 1, 0.5200000000000002)

srgb_to_linear(*col)
# Values to be set in the RGB tab of the color picker:
# (0.03310476657088504, 1.0, 0.23302199930143835)

While the HSV tab of the color picker doesn't give any indication as to whether the values are gamma corrected, this ticket does indicate that the displayed HSV values actually are gamma corrected as well. This would explain why the Hex representation does match the Hex value shown by various color converters.

So, to apply a non-linear HSV color to your object, would have to call

col = srgb_to_linear(*colorsys.hsv_to_rgb(0.4, 0.8, 1))
bpy.data.materials["name"].diffuse_color = col