A Python (3) class for figuring out the width and height of a formatted svg text.

svg_text_length.py

#!/usr/bin/env python3
# -*- coding: utf-8 -*-


# Loosely based on http://stackoverflow.com/a/28741636/1672565 


import subprocess
import struct
import os


class svg_text_length(object):
	
	
	def __init__(
		self, text = 'Hello World',
		font = 'Arial', font_size = 10, font_weight = 400, font_style = 'normal',
		clean_up = True
		):
		
		# Cross-platform ...
		temp_svg_name = 'temp_svg_text_length.svg'
		temp_png_name = 'temp_svg_text_length.png'
    
		# Speeding this thing up on Linux for lots of queries!
		# temp_svg_name = '/dev/shm/temp_svg_text_length.svg'
		# temp_png_name = '/dev/shm/temp_svg_text_length.png'
		
		svg_cnt = self.__get_dummy_svg__(text, font, font_size, font_weight, font_style)
		self.__write_text__(temp_svg_name, svg_cnt)
		self.__convert_svg2png__(temp_svg_name, temp_png_name)
		png_cnt = self.__read_binary__(temp_png_name)
		self.width, self.height = self.__get_image_info__(png_cnt)
		if clean_up:
			self.__clean_up__([temp_svg_name, temp_png_name])
	
	
	def get_size(self):
		
		return self.width, self.height
	
	
	def get_width(self):
		
		return self.width
	
	
	def __clean_up__(self, file_names):
		
		for file_name in file_names:
			os.remove(file_name)
	
	
	def __convert_svg2png__(self, dest, targ):
		
		# TODO not exactly cross platform ...
		inkscape_p = subprocess.Popen(
			['inkscape', '-f', dest, '-e', targ, '-d', '90', '-D'],
			stdin = subprocess.PIPE,
			stdout = subprocess.PIPE
			)
		inkscape_out = inkscape_p.communicate()[0].decode(encoding = 'UTF-8')
	
	
	def __get_dummy_svg__(self, text, font, font_size, font_weight, font_style):
		
		return '''
		<svg xmlns="http://www.w3.org/2000/svg">
			<text 
				font-weight="%d" font-size="%0.2f" font-family="%s" letter-spacing="0" 
				font-style="%s" word-spacing="0">
				<tspan font-family="%s">%s</tspan>
			</text>
		</svg>
		''' % (font_weight, font_size, font, font_style, font, text)
	
	
	def __get_image_info__(self, data):
		
		if self.__is_png__(data):
			w, h = struct.unpack('>LL', data[16:24])
			width = int(w)
			height = int(h)
		else:
			raise Exception('not a png image')
		
		return width, height
	
	
	def __is_png__(self, data):
		
		return (data[:8] == b'\x89PNG\r\n\x1a\n'and (data[12:16] == b'IHDR'))
	
	
	def __read_binary__(self, file_name):
		
		f = open(file_name, 'rb')
		data = f.read()
		f.close()
		
		return data
	
	
	def __write_text__(self, file_name, cnt):
		
		f = open(file_name, 'w')
		f.write(cnt)
		f.close()


if __name__ == '__main__':
	
	print(svg_text_length(
		text = 'Hello world! Even more text.',
		font = 'Arial',
		font_size = 25.0,
		font_weight = 400,
		font_style = 'italic',
		clean_up = False
		).get_size())