add content to existing docx with python-docx

I’d like to open an existing word document where I already added page numbers and just add some text and headline to it.

Here’s a basic example of how I tried to accomplish my goal

#!/usr/bin/env python 
from docx import Document
document = Document('report-template.docx')
document.add_heading('Headline No. 1', level=1)
document.add_paragraph('Test No. 1')
document.add_heading('Heading No. 2', level=2)
document.add_paragraph('Test No. 2')
document.save('example.docx')

When I do the above mentioned with a complete fresh document everything works fine – when doing this with the already existing file it fails with the following error

Traceback (most recent call last):
  File "create-report-test.py", line 6, in <module>
    document.add_heading('Headline No. 1', level=1)
  File "/usr/lib/python2.7/site-packages/docx/document.py", line 43, in add_heading
    return self.add_paragraph(text, style)
  File "/usr/lib/python2.7/site-packages/docx/document.py", line 63, in add_paragraph
    return self._body.add_paragraph(text, style)
  File "/usr/lib/python2.7/site-packages/docx/blkcntnr.py", line 38, in add_paragraph
    paragraph.style = style
  File "/usr/lib/python2.7/site-packages/docx/text/paragraph.py", line 111, in style
    style_or_name, WD_STYLE_TYPE.PARAGRAPH
  File "/usr/lib/python2.7/site-packages/docx/parts/document.py", line 75, in get_style_id
    return self.styles.get_style_id(style_or_name, style_type)
  File "/usr/lib/python2.7/site-packages/docx/styles/styles.py", line 113, in get_style_id
    return self._get_style_id_from_name(style_or_name, style_type)
  File "/usr/lib/python2.7/site-packages/docx/styles/styles.py", line 143, in _get_style_id_from_name
    return self._get_style_id_from_style(self[style_name], style_type)
  File "/usr/lib/python2.7/site-packages/docx/styles/styles.py", line 57, in __getitem__
    raise KeyError("no style with name '%s'" % key)
KeyError: u"no style with name 'Heading 1'"

I read the documention under http://python-docx.readthedocs.org/en/latest/user/documents.html but it seems I’m missing something – anyone got an idea?

Thanks in advance

Answer

python-docx can only work with styles that are already defined in the document. This error indicates that the Heading 1 paragraph style is not defined. Word starts out with no styles defined (ok, a couple like Normal, but that’s all), then it adds built-in styles to the file the first time they’re used.

Two options:

1. Add a Heading 1 paragraph to the document by hand and then delete it. After that, the Heading 1 paragraph style will be defined in the document. Once Word adds a style it doesn’t remove it, even if all paragraphs using that style are deleted.

2. Use python-docx to define Heading 1 yourself. See the documentation here on how to do that: http://python-docx.readthedocs.org/en/latest/user/styles-using.html#define-paragraph-formatting

This page is probably also worth a quick read to fill in some style concepts: http://python-docx.readthedocs.org/en/latest/user/styles-understanding.html