如何用Python解析SVG中polyline的points（支持URL与本地文件）

Got it, let's break down how to solve this problem efficiently. You need to pull SVG content (either from a URL or local file), extract all <polyline> elements, convert their points attribute into structured [[x,y], [x,y], ...] coordinate lists, and output each one individually.

Step 1: Install Required Libraries #

We'll use BeautifulSoup for parsing the SVG/XML structure and requests to fetch content from URLs. Install them via pip:

pip install beautifulsoup4 requests

Step 2: Full Example Code #

This script handles both URL and local SVG files, processes each <polyline>, and formats the points as requested:

from bs4 import BeautifulSoup
import requests

def parse_svg_polylines(source, is_url=True):
    # Get SVG content
    if is_url:
        response = requests.get(source)
        response.raise_for_status()  # Raise error if request fails
        svg_content = response.text
    else:
        with open(source, 'r') as f:
            svg_content = f.read()
    
    # Parse SVG with BeautifulSoup
    soup = BeautifulSoup(svg_content, 'xml')
    polylines = soup.find_all('polyline')
    
    # Process each polyline's points
    for idx, polyline in enumerate(polylines, 1):
        points_attr = polyline.get('points', '')
        if not points_attr:
            print(f"Polyline {idx}: No points attribute found")
            continue
        
        # Convert points string to [[x,y], ...] format
        coordinate_pairs = []
        for point_str in points_attr.split():
            x_str, y_str = point_str.split(',')
            try:
                x = float(x_str)
                y = float(y_str)
                coordinate_pairs.append([x, y])
            except ValueError:
                print(f"Polyline {idx}: Skipping invalid point '{point_str}'")
        
        print(f"Polyline {idx} coordinates:")
        print(coordinate_pairs)
        print("---")

# Example usage with your provided SVG URL
svg_url = "http://colorillo.com/bx0l.inline.svg"
parse_svg_polylines(svg_url, is_url=True)

# To use a local SVG file instead, uncomment this line:
# parse_svg_polylines("path/to/your/file.svg", is_url=False)

How It Works #

1. Fetch/Read SVG Content: The function first retrieves SVG data—either via HTTP request for URLs or reading directly from a local file.
2. Parse SVG: BeautifulSoup parses the SVG as XML, making it easy to find all <polyline> elements.
3. Process Points: For each polyline:
   • Extract the points attribute value (a string like "239,274 239,274 ...").
   • Split the string by spaces to get individual point strings.
   • Split each point string by commas, convert to numeric values, and build the coordinate list.
   • Output the formatted list, with error handling for invalid points.

Alternative: Using svgpathtools #

If you need more advanced SVG manipulation later, consider the svgpathtools library. It's designed specifically for SVG path/polyline handling:

pip install svgpathtools

A quick snippet to extract polyline points:

from svgpathtools import svg2paths

paths, attributes = svg2paths("http://colorillo.com/bx0l.inline.svg")
for idx, attr in enumerate(attributes, 1):
    if 'points' in attr:
        points = attr['points']
        # Same parsing logic as above to convert to [[x,y], ...]
        coordinate_pairs = [[float(coord) for coord in point.split(',')] for point in points.split()]
        print(f"Polyline {idx} coordinates:")
        print(coordinate_pairs)
        print("---")

This solution gives you exactly what you need: structured coordinate lists from every <polyline> in your SVG, whether it's hosted online or stored locally.

内容的提问来源于stack exchange，提问作者Ecks