Insert default/template chart into placeholder?

[just4jin]

Thanks a lot for creating this useful tool!

I have a problem when trying to insert charts which are based on my customized chart template into multiple placeholders. I create a chart template which has line and bar types and a few edits on text direction and coloring, and saved it as my default chart. However, I don't know how to insert such charts into placeholders. Is there a way to do placeholder.insert_chart(XL_CHART_TYPE.DEFAULT, chart_data)? Appreciate if you can point out a way to solve this issue.

Jin

[jdelight]

@just4jin did you find a work around / solution to this? @scanny Any idea how we could customise chart styles if not using templates? For example changing the background colour for a chart? Thanks

[scanny]

@just4jin I'm not exactly sure what you're proposing. I think you'll need to spell it out a bit more as far as what behaviors you'd like to see. Are you saying put a chart in a chart placeholder and just replace the data? That you can do today with Chart.replace_data(). That will respect all the formatting and other customization that you've already done.

[scanny]

@jdelight Chart styles are a thing, and there's a way to specify which one to apply to a chart, I think it's chart.chart_style = {n in range 1-48}. However these chart styles are formed by a built-in PowerPoint algorithm that combines theme color choices and "effect" styles. I think it's 6 color combos X 8 effect styles. Both of these are defined in the theme. An effect is like what 3D effect, shadow or no, gradient, maybe transparency, etc.

A customized chart style cannot be defined by an end-user (or anyone else). However, a lot of what they do can be customized by customizing the theme in the template you're using.

There is a mechanism, I think it's called chart themes or something, I believe the files end in '.thmx'. These are each a separate file that can be stored in the PowerPoint templates directory. I'm not sure of their exact behavior, and they're not supported in python-pptx as of yet, but might be something to explore.

[jdelight]

Thanks @scanny - yes we have chart templates which we can easily apply in the PowerPoint UI. I've had a look using opc-diag at the resulting pptx after applying a chart template and looks like there are a few extra rels/files added to the charts folder. So it seems like the options are either:

a) apply the individual styles manually to each chart (legend, label, fonts / colours etc...) and figure out how the background colour for a chart can be set (still not sure on that one)

b) use opc-diag to unpack the pptx, add the extra raw files (e.g. theme.xml, colours.xml) and somehow re-link them back to the chart, then repackage the files.

A customized chart style cannot be defined by an end-user (or anyone else). However, a lot of what they do can be customized by customizing the theme in the template you're using.

This also sounds like a good approach - so will give that a go.

Great library btw and really well documented 👍

[scanny]

@jdelight I'm actually working on something now that might need something like this. Can you say a bit more about your use case and how you do it manually, like what set of chart templates you keep around, like "one for this, a different one for that, this other one works for all these"?

Maybe we can thing about something like Chart.apply_template('templates/my-chart.crtx').

[jdelight]

That API would be fantastic! chart.apply_template('templates/my-chart.crtx').

Our use case is that we have an analytics application which allows users to create several types of charts (line, bar, horizontalBar, pie etc...). Our UX designers have created a reference PPTX file with examples of how each type of chart should look. At the moment we're recreating the look of each chart as we dynamically build pptx presentations.

For example, certain type of clustered column charts need to have legends, other charts may not need a legend or title for example.

So the ideal workflow is that we save a set of chart templates from our reference pptx file.
Then as we build presentations we can just apply the correct template - based on arbitrary metadata for the chart.

The real benefit here is that our UX designers can create a set of chart templates within the Powerpoint UI and we (developers) don't really need to worry about the effects. We can just say given chart type "x", apply template "y".

One other thing is that it's possible to have chart templates show/hide chart elements. So a chart template could show axis titles or trendlines.

If that API existed and we could apply templates - would it be possible to manipulate things like chart axis titles even though there's not an API for it in python-pptx yet.

If it is possible then in theory that opens up a lot of functionality for developers in that they can store/apply chart templates then dive into the underlying xml to update content/text etc...

I'd be happy to help work on this as it's something we feel will save us time and immediate improve the quality of our generated powerpoint files. I need to skill up a bit on openxml but let me know if there's a way I can help.

[scanny]

That's great @jdelight :) The first step would be for us to flesh out an enhancement proposal page (what I used to call "analysis page"). The key purposes for that are:

1. Agree on the API/calling protocol (fairly trivial in this case I think)
2. Work out the scope, both full general scope of the completed feature, and what makes sense as a chunk to bite off initially. In this case I think it would mostly be a statement of expected behaviors.
3. Collect all the technical documentation elements (schema excerpt, any MS API references and enumerations, specimen XML) we'll need to plan and execute the implementation.

These are located here; this new one could be named cht-apply-template.rst:
https://github.com/scanny/python-pptx/tree/master/docs/dev/analysis

The enhancement proposal is mergeable separately, even if we decided not to go forward with implementation (never happened so far :).

I'm thinking the key questions in this case will be:

• What is contained in a chart template (and what is specifically not?). At a glance it looks like everything except the series data points is included, but it will take some snooping around and probably some before/after comparisons with opc-diag to confirm that.
• What does PowerPoint do when you apply a template to a chart? This can also be determined by before/after XML diffs.

Let me know if you're keen and if there are any details you need me to help with :)

[jdelight]

Thanks for the thorough outline @scanny - I've checked with the team to decide if we have time to start on this. We don't right at the moment. But one of the things we're wondering is with the current release assuming we have a chart instance - is it possible to do something like:

chart.element.insert_some_xml_after_element([xml string])

I'm thinking specifically if we can just drop in some xml for a chart title for example.
I didn't seem to find much around manipulating the underlying xml - but I got the impression it was possible. If you could point to some useful docs or part of the code base that would be great.

[scanny]

@jdelight Apologies for a delayed reply, lost track of this one. You can use the "oxml layer" to do what you want; actually a combination of some base lxml API and some of the oxml wrapper. The oxml layer is just the code in pptx.oxml that provides some wrapper on lxml. The key modules are probably oxml (init.py), oxml.ns, and oxml.xmlchemy.

Basically I'd find the element of interest with XPath:

element = other_element.xpath('.//c:title')[0]

then use oxml/lxml operations to add some stuff after:

new_subtree = parse_xml(new_xml)
element.addnext(new_subtree)

The lxml API for the _Element class is here:
http://lxml.de/api/lxml.etree._Element-class.html

All XML elements in python-pptx derive from that class and also from oxml.xmlchemy.BaseOxmlElement.

If you search around on 'python-pptx OR python-docx workaround function' you'll find some other approaches.

[jdelight]

Fantastic thanks @scanny - will give that a go.

[tim-mukhin]

@scanny Is there a chance that it will ever be completed? I have exactly the same situation as in the comment of @jdelight