Convert hex string to hex number in python without loss of precision

Question

So, I am using the answer to this question to color some values I have for some polygons to plot to a basemap instance. I modified the function found in that link to be the following. The issue I'm having is that I have to convert the string that it returns to a hex digit to use so that I can color the polygons. But when I convert something like "0x00ffaa" to a python hex digit, it changes it to be "0xffaa", which cannot be used to color the polygon

How can I get around this?

Here is the modified function:

def rgb(mini,maxi,value):
    mini, maxi, value = float(mini), float(maxi), float(value)
    ratio = 2* (value - mini) / (maxi-mini)
    b = int(max(0,255*(1-ratio)))
    r = int(max(0,255*(ratio -1)))
    g = 255 - b - r
    b = hex(b)
    r = hex(r)
    g = hex(g)
    if len(b) == 3:
        b = b[0:2] + '0' + b[-1]
    if len(r) == 3:
        r = r[0:2] + '0' + r[-1]
    if len(g) == 3:
        g = g[0:2] + '0' + g[-1]
    string = r+g[2:]+b[2:]
    return string

So, just to make this clear for other people like me who have flawed understandings, rgb values must be passed in the form '#00ffaa', notice the pound symbol. See http://matplotlib.org/api/colors_api.html . — K. Shores, Oct 12 '15 at 19:46

score 1 · Answer 1 · answered Oct 12 '15 at 19:20

1

Use string formatting, for example:

>>> "0x%08x" % 0xffaa
'0x0000ffaa'

answered Oct 12 '15 at 19:20

cdarke

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score 1 · Accepted Answer · edited May 23 '17 at 11:52

1

The answer from cdarke is OK, but using the % operator for string interpolation is kind of deprecated. For the sake of completion, here is the format function or the str.format method:

>>> format(254, '06X')
'0000FE'

>>> "#{:06X}".format(255)
'#0000FF'

New code is expected to use one of the above instead of the % operator. If you are curious about "why does Python have a format function as well as a format method?", see my answer to this question.

But usually you don't have to worry about the representation of the value if the function/method you are using takes integers as well as strings, because in this case the string '0x0000AA' is the same as the integer value 0xAA or 170.

edited May 23 '17 at 11:52

Community

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answered Oct 12 '15 at 19:28

Paulo Scardine

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This helps, yet I'm not sure that I understand how to use it. What I am using right now is color_string.format(255), which will give me something like "0x00ffaa" (for whatever input that needs to be). But I need to pass the color as a hex digit, so then I use hex(int(color_string,16)) which then puts the number back to "0xffaa", which cannot be used as an rgb color value. Does that help explain my confusion? – K. Shores Oct 12 '15 at 19:39
Except the real format that is expected is '#000000', isn't it? Yay, flaws in understanding! – K. Shores Oct 12 '15 at 19:44

Convert hex string to hex number in python without loss of precision

2 Answers2