Python Regular Expressions Return Floating Points

Question

For a project I have to extract the RGB values from a file which are defined as following:

#71=IFCCOLOURRGB($,0.75,0.73,0.6800000000000001);
#98=IFCCOLOURRGB($,0.26,0.22,0.18);

I want to retun the RGB data and write it to a new file like this:

0.75 0.73 0.68

0.26 0.22 0.18

So far I've created this for loop:

import re 

IfcFile = open('IfcOpenHouse.ifc', 'r')

IfcColourRGB = re.compile('ifccolourrgb', re.IGNORECASE)


for rad_rgb_data in IfcFile:
    if re.search(IfcColourRGB, rad_rgb_data):
        print(IfcColourRGB.sub('', rad_rgb_data))

This returns:

#71=($,0.75,0.73,0.6800000000000001);

#98=($,0.26,0.22,0.18);

Now I am quite new to programming and I want to know if I've chosen the right approach for my task, I've been reading about regular expressions but I don't fully understand how to get rid of all the #=(,: characters and how to exactly specify which numbers you want returned and which not. Is it possible to define all regular expressions explicitly/individually and combining them in one for loop so I have an easier time understanding them?

You might not need to use regex, you could just split the string on the "," — joeButler
– joeButler, Commented Jan 8, 2015 at 17:27
Agreed but regex have the advantage to be less specific on the formated string. I mean you can change the way you store it and don't have to change this part of the code (the reading one). — 0xmax
– 0xmax, Commented Jan 8, 2015 at 17:31

Kasravnd · Accepted Answer · 2015-01-08 17:26:18Z

2

You can use re.findall() with a positive look-behind pattern , then split with , and convert to float :

>>> s="""#71=IFCCOLOURRGB($,0.75,0.73,0.6800000000000001);
... #98=IFCCOLOURRGB($,0.26,0.22,0.18);"""
>>> import re
>>> l=re.findall(r'(?<=\$,)[\d\.,]+',s)
>>> [map(float,i.split(',')) for i in l]
[[0.75, 0.73, 0.68], [0.26, 0.22, 0.18]]

answered Jan 8, 2015 at 17:26

Kasravnd

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beroe · Accepted Answer · 2015-01-08 17:57:02Z

0

I think you are overthinking this :^) You can loop through the lines and perform this search on each.

import re
Searcher = re.compile("IFCCOLOURRGB\(\$,([\d\.]+),([\d\.]+),([\d\.]+)")

for Line in IfcFile:
    Result = Searcher.search(Line)
    if Result:
        print Result.groups()

If you are just writing the values back out to a file, you don't need to convert to float after,except to truncate the 00000001 and print to 2 significant figures.

answered Jan 8, 2015 at 17:57

beroe

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Andie2302 · Accepted Answer · 2015-01-08 17:44:03Z

0

To extract the colors use:

IFCCOLOURRGB\((?P<Red>\.[0-9]{1,16}|[0-9]+(?:\.[0-9]{1,16})?),(?P<Green>\.[0-9]{1,16}|[0-9]+(?:\.[0-9]{1,16})?),(?P<Blue>\.[0-9]{1,16}|[0-9]+(?:\.[0-9]{1,16})?)\)

Capturing groups:

Red: value of red Green: value of green, Blue: value of blue

match = re.search(r"IFCCOLOURRGB\((?P<Red>\.[0-9]{1,16}|[0-9]+(?:\.[0-9]{1,16})?),(?P<Green>\.[0-9]{1,16}|[0-9]+(?:\.[0-9]{1,16})?),(?P<Blue>\.[0-9]{1,16}|[0-9]+(?:\.[0-9]{1,16})?)\)", subject)
if match:
    result1 = match.group("Red")
    result2 = match.group("Green")
    result3 = match.group("Blue")       
else:
    result = ""

answered Jan 8, 2015 at 17:44

Andie2302

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