Questions on a couple of what I suspect are standard matplotlib idioms

Couldn't see the answers to these questions when looking through the
class reference docs, but they seem like common tasks, so I suspect
there are standard idiomatic way of doing these. Could anyone refer
me to examples showing

1) How to most easily label the x axis for data which is plotted
by date? (More specifically; does matplotlib have any understanding
of date values, and if so, how do I access and use it?) I'm hoping
there's an easier way than explicitly labelling ticks on the x axis.

2) I'll be drawing logy graphs, and I want a certain slope to indicate
a certain rate of growth, which means that, when using matplotlib
via TkAgg, I want it to keep the ratio of the graph display height
and display width constant as it resizes the graph to take into
account changes in the size of the enclosing window. Is there
a standard way to do this?

Ken McDonald