Plotly python: totally free?

I'm a bit confused about the 'free' status of the Python library, Plotly.

It says on its website that it's free and open source, but at the same time it says you'll need a Plotly account if you want to publish the graphs on the web.

I want to build a web application which leverages the plotly Python and JavaScript libraries - can I do that without a plotly account?

EDIT: If you're going to downvote the question, please be so kind as to explain how it could be improved.

Short: Yes the python library is free.

Answer with sources:

I also started to use plotly and I totally agree with you that it is not very clear at first if plotly is free or not. Here are the facts I found about plotly:

  • The python library is free and is published under the MIT-License Source
  • The JS-libs are published under the MIT-License since 2015 (Source). So it also free since 2015. Here is also a link to the open-source announcement of plotly.js from 2015 Source

In the open-source announcement there is also this information about the other librarys of plotly:

The R, Python, and MATLAB clients for Plotly have always been open-source, while the core graphics layer—plotly.js—was closed-source. Now the entire stack is open-source. Source

The Accounts you can create on their website are just to host graphs online. Like with a free account you can host one private graph, with a professional account you can host unlimited private/public graphs. Link

It is a pretty common business model to make the code open-source and earn the money with providing support / or in the example of plotly hosting graphs for you if you don't want to host them on your own.

UPDATE: 20.10.2016 : Since this Question gets a lot of attention I updated the sources