使用Python解析OSM XML提取含bridge标签的way节点至CSV

Hey there! Let's break down why you're hitting that AttributeError and get your code working to extract bridge ways into a CSV like you need.

What's Causing the Error? #

Your current code uses way.find('.//tag') which only grabs the first tag inside a way. Here's the double problem:

• If a way has no tags at all, this returns None, and trying to access tag.attrib immediately throws an AttributeError.
• Even if there are tags, you're only checking the first one—so you'll miss ways where the bridge tag isn't the first in the list.

Corrected Code to Extract Bridge Ways & Save to CSV #

This code will handle your large OSM file safely, filter out only the ways with bridge=yes tags, and save all their complete details to a CSV:

import xml.etree.ElementTree as ET
import csv

# Define columns for our CSV (adjust if you need extra fields)
csv_columns = [
    'way_id', 'visible', 'version', 'changeset', 'timestamp', 'user', 'uid',
    'nd_refs', 'all_tags'
]

# Set up the CSV file for writing
with open('bridge_ways.csv', 'w', newline='', encoding='utf-8') as csvfile:
    writer = csv.DictWriter(csvfile, fieldnames=csv_columns)
    writer.writeheader()

    # Iterate through XML efficiently (critical for large files to save memory)
    for event, elem in ET.iterparse('MER.xml', events=('start', 'end')):
        if event == 'end' and elem.tag == 'way':
            # Check if this way has a bridge=yes tag
            is_bridge = False
            tag_dict = {}
            for tag in elem.findall('tag'):
                tag_key = tag.attrib.get('k')
                tag_val = tag.attrib.get('v')
                tag_dict[tag_key] = tag_val
                if tag_key == 'bridge' and tag_val == 'yes':
                    is_bridge = True

            if is_bridge:
                # Collect all data from the matching way
                way_details = {
                    'way_id': elem.attrib.get('id'),
                    'visible': elem.attrib.get('visible'),
                    'version': elem.attrib.get('version'),
                    'changeset': elem.attrib.get('changeset'),
                    'timestamp': elem.attrib.get('timestamp'),
                    'user': elem.attrib.get('user'),
                    'uid': elem.attrib.get('uid'),
                    # Combine node refs into a comma-separated string
                    'nd_refs': ','.join([nd.attrib.get('ref') for nd in elem.findall('nd')]),
                    # Format all tags into a readable string
                    'all_tags': ','.join([f"{k}:{v}" for k, v in tag_dict.items()])
                }
                writer.writerow(way_details)

            # Clear element from memory to avoid bloating with large files
            elem.clear()

print("Done! All bridge ways have been saved to bridge_ways.csv")

Key Improvements: #

• Safe Tag Checking: We loop through all tags in a way, so we never miss bridge tags that aren't first, and avoid None-related errors.
• Memory Efficiency: Using ET.iterparse() and clearing elements after processing keeps memory usage low—perfect for your 4000-way OSM file.
• Complete Way Data: The CSV includes every core attribute of the way, all node references, and all associated tags, so you get the full way information as requested.
• Error Resilient: Using .get() for attribute access prevents crashes if an optional attribute is missing from a way.

Example CSV Output Snippet: #

way_id,visible,version,changeset,timestamp,user,uid,nd_refs,all_tags
108534076,true,1,7866393,2011-04-15T02:42:51Z,richlv,47892,1245024935,1245025038,bridge:yes,highway:service

内容的提问来源于stack exchange，提问作者John Smith