Parse svg:path d attribute

Question

I need to decipher a path element in an SVG document to drive a CNC machine along that path. I wonder if there are any Python libraries that parse SVG and give some sort of pythonic list for the d attribute, e.g.:

<path d="M 20 30 L 20 20 20 40 40 40"/>

parses into

[["M", 20, 30],
 ["L", 20, 20],
 ["L", 20, 40],
 ["L", 40, 40]]

Answer 1

Getting the d-string can be down in a couple lines using svgpathtools, the rest can be done using regular expressions.

from svgpathtools import svg2paths
paths, attributes = svg2paths('some_svg_file.svg')

paths is a list of svgpathtools Path objects (containing just the curve info, no colors, styles, etc.). attributes is a list of dictionary objects of the attributes.

Suppose the path you are interested in is the first (the 0th) listed in your SVG, then to extract just the d-string you can use:

d = attributes[0]['d']  # d-string from first path in SVG

# Now for some regular expressions magic
import re
split_by_letters = re.findall('[A-Z|a-z][^A-Z|a-z]*', d)
split_as_you_want = []
for x in split_by_letters:
    nums = x[1:].replace(',',' ').split()  # list of numbers after letter
    for k in range(len(nums) // 2):
        split_as_you_want.append([x[0]] +  [nums[k]] + [nums[k+1]])
print split_as_you_want

I didn't convert the numbers into strings here as how you want to do that depends on whether they're always integers and whether you care they stay that way. For most purposes this can be done with something like the following right below the "nums = ..." line.

for k, n in enumerate(nums):
    try:
        nums[k] = int(n)
    except ValueError:
        nums[k] = float(n)

Answer 2

Here's a start it's written by me and in python 2.7.2. Just delete the tests and print statements if you want to.

   Copyright 2012 Christopher L. Ramsey

   Licensed under the Apache License, Version 2.0 (the "License");
   you may not use this file except in compliance with the License.
   You may obtain a copy of the License at

       http://www.apache.org/licenses/LICENSE-2.0

   Unless required by applicable law or agreed to in writing, software
   distributed under the License is distributed on an "AS IS" BASIS,
   WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
   See the License for the specific language governing permissions and
   limitations under the License.

from collections import OrderedDict
from re import match
from re import split
from re import sub

class PathIterator(object):
    EOI = 'End of Iteration'
    PATH_IDENTIFIERS = r'[MLHVCSQTAmlhvcsqa]'
    NUMBERS = r'[0-9.-^A-z]'
    SEPERATORS = r'\s|\,'
    PATH_END = r'[Zz]'

    def __init__(self, path):
        self.parseable = path.translate(None, '\t\f')
        self.parseable = self.parseable.replace('\n', ' ')
        print 'strip_newlines: {}'.format(self.parseable)
        self.parseable = sub(r'([A-Za-z])([0-9]|\-)', self.insert, self.parseable)
        print 'add_space: {}'.format(self.parseable)
        self.parseable = self.parseable.replace(',', ' ')
        print 'replace_commas: {}'.format(self.parseable)
        self.parseable = sub(r'\s+', ' ', self.parseable) # replace any double space with a single space
        print 'strip_extra_space: {}'.format(self.parseable)
        self.tokens = split(' ', self.parseable)
        self.map = self.produce_map(self.tokens)
        print self.map
        self.elements = self.process(self.map)

    def produce_map(self, tkns):
        self.m = OrderedDict()
        self.i = 0
        while self.i < len(tkns):
            if match(self.PATH_IDENTIFIERS, tkns[self.i]):
                self.m[self.i] = tkns[self.i]
            elif match(self.PATH_END, tkns[self.i]):
                self.m[self.i] = tkns[self.i]
            else:
                pass
            self.i += 1
        return self.m.items()

    def process(self, map):
        self.mm = []
        self.l = len(map)
        for e in range(self.l):
            try:
                self.element = map[e]
                self.future = map[e + 1]
                self.ident = self.element[1]
                self.start = self.element[0] + 1
                self.end = self.future[0]
                self.nbrs = self.tokens[self.start:self.end]
            except:
                self.element = map[e]
                self.ident = self.element[1]
                self.start = self.element[0] + 1
                self.end = len(self.tokens)
                self.nbrs = self.tokens[self.start:self.end]
                print 'start: {} end {}'.format(self.start, self.end)
            finally:
                self.numbers = []
                for number in self.nbrs:
                    self.numbers.append(float(number))
                self.mm.append((self.ident, self.numbers))
        return iter(self.mm)

    def next(self):
        try:
            return self.elements.next()
        except:
            return self.EOI

    def insert(self, match_obj):
        self.group = match_obj.group()
        return '{} {}'.format(self.group[0], self.group[1])

if __name__ == '__main__':
    inkscape_path = "M 12,90 C 8.676,90 6,87.324 6,84 L 6,82 6,14 6,12 c 0,-0.334721 0.04135,-0.6507 0.09375,-0.96875 0.0487,-0.295596 0.09704,-0.596915 0.1875,-0.875 C 6.29113,10.12587 6.302142,10.09265 6.3125,10.0625 6.411365,9.774729 6.5473802,9.515048 6.6875,9.25 6.8320918,8.976493 7.0031161,8.714385 7.1875,8.46875 7.3718839,8.223115 7.5612765,7.995278 7.78125,7.78125 8.221197,7.353194 8.72416,6.966724 9.28125,6.6875 9.559795,6.547888 9.8547231,6.440553 10.15625,6.34375 9.9000482,6.443972 9.6695391,6.580022 9.4375,6.71875 c -0.00741,0.0044 -0.023866,-0.0045 -0.03125,0 -0.031933,0.0193 -0.062293,0.04251 -0.09375,0.0625 -0.120395,0.0767 -0.2310226,0.163513 -0.34375,0.25 -0.1061728,0.0808 -0.2132809,0.161112 -0.3125,0.25 C 8.4783201,7.442683 8.3087904,7.626638 8.15625,7.8125 8.0486711,7.942755 7.9378561,8.077785 7.84375,8.21875 7.818661,8.25713 7.805304,8.30462 7.78125,8.34375 7.716487,8.446782 7.6510225,8.548267 7.59375,8.65625 7.4927417,8.850956 7.3880752,9.071951 7.3125,9.28125 7.30454,9.30306 7.288911,9.3218 7.28125,9.34375 7.2494249,9.4357 7.2454455,9.530581 7.21875,9.625 7.1884177,9.731618 7.1483606,9.828031 7.125,9.9375 7.0521214,10.279012 7,10.635705 7,11 l 0,2 0,68 0,2 c 0,2.781848 2.2181517,5 5,5 l 2,0 68,0 2,0 c 2.781848,0 5,-2.218152 5,-5 l 0,-2 0,-68 0,-2 C 89,10.635705 88.94788,10.279012 88.875,9.9375 88.83085,9.730607 88.78662,9.539842 88.71875,9.34375 88.71105,9.3218 88.69545,9.30306 88.6875,9.28125 88.62476,9.107511 88.549117,8.913801 88.46875,8.75 88.42717,8.6672 88.38971,8.580046 88.34375,8.5 88.28915,8.40279 88.216976,8.31165 88.15625,8.21875 88.06214,8.077785 87.951329,7.942755 87.84375,7.8125 87.700576,7.63805 87.540609,7.465502 87.375,7.3125 87.36383,7.3023 87.35502,7.29135 87.34375,7.28125 87.205364,7.155694 87.058659,7.046814 86.90625,6.9375 86.803679,6.86435 86.701932,6.784136 86.59375,6.71875 c -0.0074,-0.0045 -0.02384,0.0044 -0.03125,0 -0.232039,-0.138728 -0.462548,-0.274778 -0.71875,-0.375 0.301527,0.0968 0.596455,0.204138 0.875,0.34375 0.55709,0.279224 1.060053,0.665694 1.5,1.09375 0.219973,0.214028 0.409366,0.441865 0.59375,0.6875 0.184384,0.245635 0.355408,0.507743 0.5,0.78125 0.14012,0.265048 0.276135,0.524729 0.375,0.8125 0.01041,0.03078 0.02133,0.06274 0.03125,0.09375 0.09046,0.278085 0.1388,0.579404 0.1875,0.875 C 89.95865,11.3493 90,11.665279 90,12 l 0,2 0,68 0,2 c 0,3.324 -2.676,6 -6,6 l -72,0 z"
    mdn_path = "M10 80 Q 52.5 10, 95 80 T 180 80"
    w3c_path = "M100,200 C100,100 250,100 250,200 S400,300 400,200"
    w3c_path_neg = "M-100,200 C100,100 250,100 250,200 S-400,300 400,200"
    w3c_path_nl = '''
           M600,350 l 50,-25
           a25,25 -30 0,1 50,-25 l 50,-25
           a25,50 -30 0,1 50,-25 l 50,-25
           a25,75 -30 0,1 50,-25 l 50,-25
           a25,100 -30 0,1 50,-25 l 50,-25
           '''
    paths = [inkscape_path, mdn_path, w3c_path, str.strip(w3c_path_nl), w3c_path_neg]
    for path in paths:
        p = PathIterator(path)
        char = ''
        while char != PathIterator.EOI:
            char = p.next()
            print char