到目前为止我有这个代码：
def make_png_download():
svg_data = Graphs.svgdata
with open('chart.svg', 'wb+') as file:
file.write(svg_data)
with wand.image.Image(blob=file.read(), format="svg") as image:
png_image = image.make_blob("png")
response = send_file(png_image, as_attachment=True, attachment_filename='chart.png')
response.headers['Content-Description'] = 'Png Download'
response.headers['Cache-Control'] = 'no-cache'
response.headers['Content-Type'] = 'image/png'
response.headers['Content-Disposition'] = 'attachment; filename=chart.png'
return response
我正在尝试写入一个文件，以便我可以使用wand导入的模块（从svg到png）转换它，但是得到错误＆＃39; wand.exceptions.BlobError：零长度blob不允许`缓冲区。 SVG＆＃39; @ error / blob.c / BlobToImage / 343＆＃39;
我认为这种情况正在发生，因为在尝试写入文件后它是空白的 - 任何人都可以告诉我在这里做错了所以我可以正确地写文件吗？
如果我打印svg_data，它会返回：
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"legend_at_bottom_columns": null, "show_minor_y_labels": true, "show_legend": true}</script><script type="text/javascript" xlink:href="https://kozea.github.io/pygal.js/2.0.x/pygal-tooltips.min.js" /></defs><title>Precentage of Absence per Team (%)</title><g class="graph pie-graph vertical"><rect class="background" height="600" width="800" x="0" y="0" /><g class="plot" transform="translate(178, 55)"><rect class="background" height="525" width="602.0" x="0" y="0" /><g class="series serie-0 color-0"><g class="slices"><g class="slice"><a xlink:href="http://127.0.0.1:4996/download-chart"><desc class="xlink">http://127.0.0.1:4996/download-chart</desc><path class="slice reactive tooltip-trigger" d="M301.000000 26.250000 A236.250000 236.250000 0 0 1 359.280948 33.551548 L320.426983 186.183849 A78.750000 78.750000 0 0 0 301.000000 183.750000 z" /><desc class="value">1.13%</desc><desc class="x centered">320.5788477886972</desc><desc class="y centered">106.22166266795955</desc></a></g></g></g><g class="series serie-1 color-1"><g class="slices"><g class="slice"><a xlink:href="http://127.0.0.1:4996/download-chart"><desc class="xlink">http://127.0.0.1:4996/download-chart</desc><path class="slice reactive tooltip-trigger" d="M359.280948 33.551548 A236.250000 236.250000 0 0 1 446.565071 76.422402 L349.521690 200.474134 A78.750000 78.750000 0 0 0 320.426983 186.183849 z" /><desc class="value">1.88%</desc><desc class="x centered">370.43510932052936</desc><desc class="y centered">121.13163156615926</desc></a></g></g></g><g class="series serie-2 color-2"><g class="slices"><g class="slice"><a xlink:href="http://127.0.0.1:4996/download-chart"><desc class="xlink">http://127.0.0.1:4996/download-chart</desc><path class="slice reactive tooltip-trigger" d="M446.565071 76.422402 A236.250000 236.250000 0 0 1 482.918572 111.769461 L361.639524 212.256487 A78.750000 78.750000 0 0 0 349.521690 200.474134 z" /><desc class="value">0.975%</desc><desc class="x centered">410.7952393652246</desc><desc class="y centered">149.57854316945327</desc></a></g></g></g><g class="series serie-3 color-3"><g class="slices"><g class="slice"><a xlink:href="http://127.0.0.1:4996/download-chart"><desc class="xlink">http://127.0.0.1:4996/download-chart</desc><path class="slice reactive tooltip-trigger" d="M482.918572 111.769461 A236.250000 236.250000 0 0 1 513.533884 159.333092 L371.844628 228.111031 A78.750000 78.750000 0 0 0 361.639524 212.256487 z" /><desc class="value">1.09%</desc><desc class="x centered">433.4365839963262</desc><desc class="y centered">177.25446510588347</desc></a></g></g></g><g class="series serie-4 color-4"><g class="slices"><g class="slice"><a xlink:href="http://127.0.0.1:4996/download-chart"><desc class="xlink">http://127.0.0.1:4996/download-chart</desc><path class="slice reactive tooltip-trigger" d="M513.533884 159.333092 A236.250000 236.250000 0 0 1 533.929875 223.031840 L378.643292 249.343947 A78.750000 78.750000 0 0 0 371.844628 228.111031 z" /><desc class="value">1.29%</desc><desc class="x centered">450.9983300131739</desc><desc class="y centered">214.4713523690395</desc></a></g></g></g><g class="series serie-5 color-5"><g class="slices"><g class="slice"><a xlink:href="http://127.0.0.1:4996/download-chart"><desc class="xlink">http://127.0.0.1:4996/download-chart</desc><path class="slice reactive tooltip-trigger" d="M533.929875 223.031840 A236.250000 236.250000 0 0 1 370.946735 488.157964 L324.315578 337.719321 A78.750000 78.750000 0 0 0 378.643292 249.343947 z" /><desc class="value">6.52%</desc><desc class="x centered">435.17488697510225</desc><desc class="y centered">344.9824205829251</desc></a></g></g></g><g class="series serie-6 color-6"><g class="slices"><g class="slice"><a xlink:href="http://127.0.0.1:4996/download-chart"><desc class="xlink">http://127.0.0.1:4996/download-chart</desc><path class="slice reactive tooltip-trigger" d="M370.946735 488.157964 A236.250000 236.250000 0 0 1 291.481953 498.558190 L297.827318 341.186063 A78.750000 78.750000 0 0 0 324.315578 337.719321 z" /><desc class="value">1.55%</desc><desc class="x centered">321.43904510959067</desc><desc class="y centered">418.6681639611868</desc></a></g></g></g><g class="series serie-7 color-7"><g class="slices"><g class="slice"><a xlink:href="http://127.0.0.1:4996/download-chart"><desc class="xlink">http://127.0.0.1:4996/download-chart</desc><path class="slice reactive tooltip-trigger" d="M291.481953 498.558190 A236.250000 236.250000 0 0 1 183.863235 467.665886 L261.954412 330.888629 A78.750000 78.750000 0 0 0 297.827318 341.186063 z" /><desc class="value">2.17%</desc><desc class="x centered">257.5440506857186</desc><desc class="y centered">413.8863615693125</desc></a></g></g></g><g class="series serie-8 color-8"><g class="slices"><g class="slice"><a xlink:href="http://127.0.0.1:4996/download-chart"><desc class="xlink">http://127.0.0.1:4996/download-chart</desc><path class="slice reactive tooltip-trigger" d="M183.863235 467.665886 A236.250000 236.250000 0 0 1 97.052895 381.746135 L233.017632 302.248712 A78.750000 78.750000 0 0 0 261.954412 330.888629 z" /><desc class="value">2.37%</desc><desc class="x centered">190.20637043159743</desc><desc class="y centered">374.44204593029195</desc></a></g></g></g><g class="series serie-9 color-9"><g class="slices"><g class="slice"><a xlink:href="http://127.0.0.1:4996/download-chart"><desc class="xlink">http://127.0.0.1:4996/download-chart</desc><path class="slice reactive tooltip-trigger" d="M97.052895 381.746135 A236.250000 236.250000 0 0 1 65.452254 280.702248 L222.484085 268.567416 A78.750000 78.750000 0 0 0 233.017632 302.248712 z" /><desc class="value">2.05%</desc><desc class="x centered">150.67975242492986</desc><desc class="y centered">309.5114153048982</desc></a></g></g></g><g class="series serie-10 color-10"><g class="slices"><g class="slice"><a xlink:href="http://127.0.0.1:4996/download-chart"><desc class="xlink">http://127.0.0.1:4996/download-chart</desc><path class="slice reactive tooltip-trigger" d="M65.452254 280.702248 A236.250000 236.250000 0 0 1 70.070074 212.645894 L224.023358 245.881965 A78.750000 78.750000 0 0 0 222.484085 268.567416 z" /><desc class="value">1.31%</desc><desc class="x centered">143.86131899861402</desc><desc class="y centered">251.83768631371902</desc></a></g></g></g><g class="series serie-11 color-11"><g class="slices"><g class="slice"><a xlink:href="http://127.0.0.1:4996/download-chart"><desc class="xlink">http://127.0.0.1:4996/download-chart</desc><path class="slice reactive tooltip-trigger" d="M70.070074 212.645894 A236.250000 236.250000 0 0 1 267.142625 28.688664 L289.714208 184.562888 A78.750000 78.750000 0 0 0 224.023358 245.881965 z" /><desc class="value">5.51%</desc><desc class="x centered">193.52774154611257</desc><desc class="y centered">147.36545408600935</desc></a></g></g></g><g class="series serie-12 color-12"><g class="slices"><g class="slice"><a xlink:href="http://127.0.0.1:4996/download-chart"><desc class="xlink">http://127.0.0.1:4996/download-chart</desc><path class="slice reactive tooltip-trigger" d="M267.142625 28.688664 A236.250000 236.250000 0 0 1 301.000000 26.250000 L301.000000 183.750000 A78.750000 78.750000 0 0 0 289.714208 184.562888 z" /><desc class="value">0.652%</desc><desc class="x centered">289.68497101008614</desc><desc class="y centered">105.40696985875724</desc></a></g></g></g></g><g class="titles"><text class="title plot_title" x="400.0" y="35">Precentage of Absence per Team (%)</text></g><g class="plot overlay" transform="translate(178, 55)"><g class="series serie-0 color-0" /><g class="series serie-1 color-1" /><g class="series serie-2 color-2" /><g class="series serie-3 color-3" /><g class="series serie-4 color-4" /><g class="series serie-5 color-5" /><g class="series serie-6 color-6" /><g class="series serie-7 color-7" /><g class="series serie-8 color-8" /><g class="series serie-9 color-9" /><g class="series serie-10 color-10" /><g class="series serie-11 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height="22" width="22" x="0.0" y="363.0" /><text x="27.0" y="378.2">Mugs</text></g><g class="legend reactive activate-serie" id="activate-serie-12"><rect class="color-2 reactive" height="22" width="22" x="0.0" y="396.0" /><text x="27.0" y="411.2">3D Sublimation</text></g></g><g class="legends" transform="translate(790, 65)" /></g></svg>'
wand.image.Image（blob =）需要一个bytearray / bytes类型的对象，我认为这是原始svg内容所必需的，因此我打开了＆＃39; wb +＆＃39;使用open（）上下文管理器的权限，但也许这在某种程度上是错误的？
我还尝试使用file.write（svg_data.encode（＆＃39; utf-8＆＃39;）写入文件时将数据编码为utf-8，但这似乎也不起作用。
编辑：
def make_png_download():
svg_data = Graphs.svgdata
with open('chart.svg', 'wb+') as file:
file.write(svg_data)
with open(file, 'rb') as rfile:
with wand.image.Image(blob=rfile.read(), format="svg") as image:
png_image = image.make_blob("png")
response = send_file(png_image, as_attachment=True, attachment_filename='chart.png')