Question

我正在尝试使用Python的ElementTree包编写XML文件。基本上我创建了一个名为allDepts的根元素，然后在我的for循环的每次迭代中，我调用一个返回deptElement的函数，该函数包含大量关于大学系的信息。我将每个deptElement添加到allDepts，从ElementTree中创建allDepts，并尝试将其写入文件。

def crawl(year, season, campus):
  departments = getAllDepartments(year, season, campus)
  allDepts = ET.Element('depts')

  for dept in departments:
    deptElement = getDeptElement(allDepts, dept, year, season, campus)
    print ET.tostring(deptElement)    #Prints fine here!
    ET.SubElement(allDepts, deptElement)

    if deptElement == None:
        print "ERROR: " + dept

  with open(str(year) + season + "_" + campus + "_courses.xml", 'w') as f:
    tree = ET.ElementTree(allDepts)
    tree.write(f)

出于某种原因，在tree.write(f)行，我收到此错误：“TypeError：无法连接'str'和'instance'对象”。每个deptElement在for循环中打印得很好，让我觉得getDeptElement()工作正常。我从未打印出“错误”消息。有谁知道我做错了什么？

编辑：这是完整的堆栈跟踪：

File "./CourseInfoCrawl.py", line 210, in <module>
crawl("2013", "S", "UBC")
File "./CourseInfoCrawl.py", line 207, in crawl
tree.write(f)
File "/System/Library/Frameworks/Python.framework/Versions/2.6/lib/python2.6/xml/etree/ElementTree.py", line 663, in write
self._write(file, self._root, encoding, {})
File "/System/Library/Frameworks/Python.framework/Versions/2.6/lib/python2.6/xml/etree/ElementTree.py", line 707, in _write
self._write(file, n, encoding, namespaces)
File "/System/Library/Frameworks/Python.framework/Versions/2.6/lib/python2.6/xml/etree/ElementTree.py", line 681, in _write
file.write("<" + _encode(tag, encoding))

Answer 1

似乎以下行是原因。

    print "ERROR: " + dept

按以下方式更改并重试：

    print "ERROR: ", dept

OR

    print "ERROR: " + str(dept)

添加

ET.SubElement的第二个参数应该是str。 deptElement是str吗？如果deptElement是元素，请使用allDepts.append(deptElement)。

http://docs.python.org/2/library/xml.etree.elementtree.html#xml.etree.ElementTree.SubElement http://docs.python.org/2/library/xml.etree.elementtree.html#xml.etree.ElementTree.Element.append

ADD 2 重现错误（Python 2.6）：

>>> from xml.etree import ElementTree as ET >>> allDepts = ET.Element('depts') >>> ET.SubElement(allDepts, ET.Element('a')) <Element <Element a at b727b96c> at b727b22c> >>> with open('a', 'wb') as f: ... tree = ET.ElementTree(allDepts) ... tree.write(f) ... Traceback (most recent call last): File "<stdin>", line 3, in <module> File "/home/falsetru/t/Python-2.6/Lib/xml/etree/ElementTree.py", line 663, in write self._write(file, self._root, encoding, {}) File "/home/falsetru/t/Python-2.6/Lib/xml/etree/ElementTree.py", line 707, in _write self._write(file, n, encoding, namespaces) File "/home/falsetru/t/Python-2.6/Lib/xml/etree/ElementTree.py", line 681, in _write file.write("<" + _encode(tag, encoding)) TypeError: cannot concatenate 'str' and 'instance' objects

重现错误（Python 2.7，不同的错误消息）：

>>> from xml.etree import ElementTree as ET >>> allDepts = ET.Element('depts') >>> ET.SubElement(allDepts, ET.Element('a')) <Element <Element 'a' at 0xb745a8ec> at 0xb74601ac> >>> with open('a', 'wb') as f: ... tree = ET.ElementTree(allDepts) ... tree.write(f) ... Traceback (most recent call last): File "<stdin>", line 3, in <module> File "/usr/lib/python2.7/xml/etree/ElementTree.py", line 817, in write self._root, encoding, default_namespace File "/usr/lib/python2.7/xml/etree/ElementTree.py", line 886, in _namespaces _raise_serialization_error(tag) File "/usr/lib/python2.7/xml/etree/ElementTree.py", line 1052, in _raise_serialization_error "cannot serialize %r (type %s)" % (text, type(text).__name__) TypeError: cannot serialize <Element 'a' at 0xb745a8ec> (type Element)

将Python ElementTree写入文件会引发TypeError

1 个答案: