python - 用utf-8编码将ElementTree直接写入zip

Question

我想修改大量的XML。它们存储在 ZIP 文件中。源 XML 是 utf-8 编码的(至少对于 Linux 上的 file 工具的猜测)并且具有正确的 XML 声明:<?xml version='1.0' encoding='UTF-8'?> 。

目标 ZIP 和其中包含的 XML 也应具有正确的 XML 声明。但是，(至少对我而言)最明显的方法(使用 ElementTree.tostring )失败了。

这是一个独立的示例，它应该是开箱即用的。
简短的演练:

导入 o​​jit_rli

准备工作(创建 src.zip，这些 ZIP 是我实际应用中给出的)

程序的实际工作(修改 XML)，从 # read XMLs from zip

开始

请关注下半部分，尤其是 # APPROACH 1 、 APPROACH 2 、 APPROACH 3 :

import os
import tempfile
import zipfile
from xml.etree.ElementTree import Element, parse

src_1 = os.path.join(tempfile.gettempdir(), "one.xml")
src_2 = os.path.join(tempfile.gettempdir(), "two.xml")
src_zip = os.path.join(tempfile.gettempdir(), "src.zip")
trgt_appr1_zip = os.path.join(tempfile.gettempdir(), "trgt_appr1.zip")
trgt_appr2_zip = os.path.join(tempfile.gettempdir(), "trgt_appr2.zip")
trgt_appr3_zip = os.path.join(tempfile.gettempdir(), "trgt_appr3.zip")

# file on hard disk that must be used due to ElementTree insufficiencies
tmp_xml_name = os.path.join(tempfile.gettempdir(), "curr_xml.tmp")

# prepare src.zip
tree1 = ElementTree(Element('hello', {'beer': 'good'}))
tree1.write(os.path.join(tempfile.gettempdir(), "one.xml"), encoding="UTF-8", xml_declaration=True)
tree2 = ElementTree(Element('scnd', {'äkey': 'a value'}))
tree2.write(os.path.join(tempfile.gettempdir(), "two.xml"), encoding="UTF-8", xml_declaration=True)

with zipfile.ZipFile(src_zip, 'a') as src:
    with open(src_1, 'r', encoding="utf-8") as one:
        string_representation = one.read()
    # write to zip
    src.writestr(zinfo_or_arcname="one.xml", data=string_representation.encode("utf-8"))
    with open(src_2, 'r', encoding="utf-8") as two:
        string_representation = two.read()
    # write to zip
    src.writestr(zinfo_or_arcname="two.xml", data=string_representation.encode("utf-8"))
os.remove(src_1)
os.remove(src_2)

# read XMLs from zip
with zipfile.ZipFile(src_zip, 'r') as zfile:

    updated_trees = []

    for xml_name in zfile.namelist():

        curr_file = zfile.open(xml_name, 'r')
        tree = parse(curr_file)
        # modify tree
        updated_tree = tree
        updated_tree.getroot().append(Element('new', {'newkey': 'new value'}))
        updated_trees.append((xml_name, updated_tree))

    for xml_name, updated_tree in updated_trees:

        # write to target file
        with zipfile.ZipFile(trgt_appr1_zip, 'a') as trgt1_zip, zipfile.ZipFile(trgt_appr2_zip, 'a') as trgt2_zip, zipfile.ZipFile(trgt_appr3_zip, 'a') as trgt3_zip:

            #
            # APPROACH 1 [DESIRED, BUT DOES NOT WORK]: write tree to zip-file
            # encoding in XML declaration missing
            #
            # create byte representation of elementtree
            byte_representation = tostring(element=updated_tree.getroot(), encoding='UTF-8', method='xml')
            # write XML directly to zip
            trgt1_zip.writestr(zinfo_or_arcname=xml_name, data=byte_representation)

            #
            # APPROACH 2 [WORKS IN THEORY, BUT DOES NOT WORK]: write tree to zip-file
            # encoding in XML declaration is faulty (is 'utf8', should be 'utf-8' or 'UTF-8')
            #
            # create byte representation of elementtree
            byte_representation = tostring(element=updated_tree.getroot(), encoding='utf8', method='xml')
            # write XML directly to zip
            trgt2_zip.writestr(zinfo_or_arcname=xml_name, data=byte_representation)

            #
            # APPROACH 3 [WORKS, BUT LACKS PERFORMANCE]: write to file, then read from file, then write to zip
            #
            # write to file
            updated_tree.write(tmp_xml_name, encoding="UTF-8", method="xml", xml_declaration=True)
            # read from file
            with open(tmp_xml_name, 'r', encoding="utf-8") as tmp:
                string_representation = tmp.read()
            # write to zip
            trgt3_zip.writestr(zinfo_or_arcname=xml_name, data=string_representation.encode("utf-8"))

    os.remove(tmp_xml_name)

APPROACH 3 有效，但它比其他两个资源密集得多。
APPROACH 2 是我可以用实际的 XML 声明来编写 ElementTree 对象的唯一方法——结果证明它是无效的( utf8 而不是 UTF-8/ utf-8 )。
APPROACH 1 将是最需要的——但在管道的稍后读取过程中失败，因为缺少 XML 声明。

问题: 如何摆脱先将整个 XML 写入磁盘，然后再读取它，将其写入 zip 并在完成 zip 后删除它？我错过了什么？

Answer 1

您可以使用 io.BytesIO 对象。
这允许使用 ElementTree.write ，同时避免将树导出到磁盘:

import zipfile
from io import BytesIO
from xml.etree.ElementTree import ElementTree, Element

tree = ElementTree(Element('hello', {'beer': 'good'}))
bio = BytesIO()
tree.write(bio, encoding='UTF-8', xml_declaration=True)
with zipfile.ZipFile('/tmp/test.zip', 'w') as z:
    z.writestr('test.xml', bio.getvalue())

如果您使用的是 Python 3.6 或更高版本，还有一个更短的解决方案:
您可以从 ZipFile 对象中获取可写文件对象，您可以将其传递给 ElementTree.write :

import zipfile
from xml.etree.ElementTree import ElementTree, Element

tree = ElementTree(Element('hello', {'beer': 'good'}))
with zipfile.ZipFile('/tmp/test.zip', 'w') as z:
    with z.open('test.xml', 'w') as f:
        tree.write(f, encoding='UTF-8', xml_declaration=True)

这还有一个优点，即您不会在内存中存储树的多个副本，这可能是大树的相关问题。