Ask HN: Best Python graphing and reporting libraries for web app

I'm building a web site that will include multiple graphs and printable reports. The graphs are pretty simple line graphs (perhaps with multiple data sources). Ideally, the graphic library would be able to do some smoothing of the data.

The reports are also fairly simple (lists of data with said graphs).

What do you think the best graphing and reporting libraries (for the planned usage) out there are?