ElementTree TypeError "write() argument must be str, not bytes" in Python3

Question

Got a Problem with generating a .SVG File with Python3 and ElementTree.

    from xml.etree import ElementTree as et
    doc = et.Element('svg', width='480', height='360', version='1.1', xmlns='http://www.w3.org/2000/svg')

    #Doing things with et and doc

    f = open('sample.svg', 'w')
    f.write('<?xml version=\"1.0\" standalone=\"no\"?>\n')
    f.write('<!DOCTYPE svg PUBLIC \"-//W3C//DTD SVG 1.1//EN\"\n')
    f.write('\"http://www.w3.org/Graphics/SVG/1.1/DTD/svg11.dtd\">\n')
    f.write(et.tostring(doc))
    f.close()

The Function et.tostring(doc) generates the TypeError "write() argument must be str, not bytes". I don't understand that behavior, "et" should convert the ElementTree-Element into a string? It works in python2, but not in python3. What did i do wrong?

Did you check the documentation? See [this page](https://docs.python.org/3/library/xml.etree.elementtree.html) and search for `tostring`. Does that help? — Ray Toal, Feb 27 '17 at 08:01
not really, it should be decoded already in utf-8 bytestring, but python3 seems to have a problem with that — Benny H., Feb 27 '17 at 08:10

score 30 · Accepted Answer · answered Feb 27 '17 at 08:11

As it turns out, tostring, despite its name, really does return an object whose type is bytes.

Stranger things have happened. Anyway, here's the proof:

>>> from xml.etree.ElementTree import ElementTree, tostring
>>> import xml.etree.ElementTree as ET
>>> element = ET.fromstring("<a></a>")
>>> type(tostring(element))
<class 'bytes'>

Silly, isn't it?

Fortunately you can do this:

>>> type(tostring(element, encoding="unicode"))
<class 'str'>

Yes, we all thought the ridiculousness of bytes and that ancient, forty-plus-year-old-and-obsolete encoding called ascii was dead.

And don't get me started on the fact that they call "unicode" an encoding!!!!!!!!!!!

It was fun to test out. I couldn't believe it when I saw the result of `type(tostring(element))`. And then seeing the result change because of a change to a parameter value. Wow. That was really weird. Nice question. — Ray Toal, Feb 27 '17 at 08:19

score 10 · Answer 2 · answered Sep 10 '19 at 01:46

10

The output file should be in binary mode.

f = open('sample.svg', 'wb')

answered Sep 10 '19 at 01:46

Dominic Bett

478
5
12

score 5 · Answer 3 · answered Feb 27 '17 at 08:04

5

Try:

f.write(et.tostring(doc).decode(encoding))

Example:

f.write(et.tostring(doc).decode("utf-8"))

answered Feb 27 '17 at 08:04

ShuzZzle

192
1
9

score 3 · Answer 4 · answered Feb 27 '17 at 08:17

3

Specify encoding of string while writing the xml file.

Like decode(UTF-8) with write(). Example: file.write(etree.tostring(doc).decode(UTF-8))

answered Feb 27 '17 at 08:17

StewieGGriffin

349
1
4
14

score 1 · Answer 5 · answered Jul 17 '18 at 09:22

For me it was the easiest to create first some template xml (just defining the root) and then parse it...

docXml = ET.parse('template.xml')
root = docXml.getroot()

then doing what I wanted to do in my xml and them print it...

docXml.write("output.xml", encoding="utf-8")

ElementTree TypeError "write() argument must be str, not bytes" in Python3

5 Answers5

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