解决Python CSV转GeoJSON时循环迭代覆盖旧条目问题

我用一段Python循环尝试将CSV文件转换为GeoJSON格式，脚本代码如下：

def make_json(csvFilePath, jsonFilePath):

    # create a dictionary
    data = {
            "type": "FeatureCollection",
            "features": []
    }

    feature = {
            "type": "Feature",
            "geometry": {
                    "type": "Point",
                    "coordinates": []
            },
            "properties": {}
    }

    # Open a csv reader called DictReader
    with open(csvFilePath, encoding='utf-8') as csvf:
        csvReader = csv.DictReader(csvf)
    
    # Convert each row into a dictionary
    # and add it to data
        for rows in csvReader:

            feature['geometry']['coordinates'] = [float(rows['s_dec']),float(rows['s_ra'])]
            feature['properties'] = rows
            data['features'].append(feature)

    # Open a json writer, and use the json.dumps()
    # function to dump data
    with open(jsonFilePath, 'w', encoding='utf-8') as jsonf:
        jsonf.write(json.dumps(data, indent=4))

运行后出现新条目覆盖旧条目的问题，所有feature内容都和最后一条数据一致，输出内容如下：

{
"type": "FeatureCollection",
"features": [
    {
        "type": "Feature",
        "geometry": {
            "type": "Point",
            "coordinates": [
                -67.33190277777777,
                82.68714791666666
            ]
        },
        "properties": {
            "dataproduct_type": "image",
            "s_ra": "82.68714791666666",
            "s_dec": "-67.33190277777777",
            "t_min": "59687.56540044768",
            "t_max": "59687.5702465162",
            "s_region": "POLYGON 82.746588309 -67.328433557 82.78394862 -67.338513769"
        }
    },
    {
        "type": "Feature",
        "geometry": {
            "type": "Point",
            "coordinates": [
                -67.33190277777777,
                82.68714791666666
            ]
        },
        "properties": {
            "dataproduct_type": "image",
            "s_ra": "82.68714791666666",
            "s_dec": "-67.33190277777777",
            "t_min": "59687.56540044768",
            "t_max": "59687.5702465162",
            "s_region": "POLYGON 82.746588309 -67.328433557 82.78394862 -67.338513769"
        }
    }
]}

问题原因 #

你在循环外部只创建了一个feature字典对象，每次循环修改它的属性并添加到features列表时，实际上是把同一个字典的引用重复添加到列表里。所有列表元素指向的都是同一个内存对象，每次循环修改的都是这个对象的内容，最终所有条目都会被最后一次修改的结果覆盖。

修正后的代码 #

把feature的定义移到循环内部，每次迭代都创建一个新的字典对象，确保每个feature都是独立的：

import csv
import json

def make_json(csvFilePath, jsonFilePath):

    # create a dictionary
    data = {
            "type": "FeatureCollection",
            "features": []
    }

    # Open a csv reader called DictReader
    with open(csvFilePath, encoding='utf-8') as csvf:
        csvReader = csv.DictReader(csvf)
    
    # Convert each row into a dictionary
    # and add it to data
        for rows in csvReader:
            # 每次循环创建新的feature对象
            feature = {
                    "type": "Feature",
                    "geometry": {
                            "type": "Point",
                            "coordinates": []
                    },
                    "properties": {}
            }
            feature['geometry']['coordinates'] = [float(rows['s_dec']),float(rows['s_ra'])]
            feature['properties'] = rows
            data['features'].append(feature)

    # Open a json writer, and use the json.dumps()
    # function to dump data
    with open(jsonFilePath, 'w', encoding='utf-8') as jsonf:
        jsonf.write(json.dumps(data, indent=4))

内容的提问来源于stack exchange，提问作者thefreeline