Datetime objects as xticklabels; getting the location of xticks

The solution notebook, cell 15, uses this line to set the xticklabels:

ax1.set_xticklabels(['', '2001', '', '2003', '', '2005', '',
                     '2007', '', '2009']

There must be a better way to do this than typing the ticklabels manually.

Also, how can I get the current xtick locations in this example?

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