Python Hour - 11 August 2014

• Cim mentioned there is a Python toolbox called x-ray (short for eXtended arRAYs) that is designed to make working with multi-dimensional datasets a lot easier. xray allows you to add dimension names and coordinate values to numpy ndarrays. You can then use those dimension names and coordinate values to perform operations over the array. For example, with xray, you can find the time mean of an array by doing something like x.sum('time') - rather than x.sum(axis=0), if time was on the first dimension.

• Jake asked about how to set the x-y aspect ratio of a plot. We talked about many ways of doing this. The easiest solution is probably to use the axes method set_aspect. An minimal working example is provided here.

• Earle talked about different ways of saving Python data to file. Several options were mentioned; for e.g. (most) data can be saved as .mat, netcdf or HDF files. However, the standard way of saving Python objects to file is to use the pickle module. The syntax for saving objects using pickle is pickle.dump(obj,file,protocol). You can find examples of how to use pickle here. By default, pickle.dump(...) tries to save data in a human-readable format. This is ok for small, simple objects but saving large n-dimensional arrays this way is very slow and results in files that take up a lot of disk space. The protocol parameter allows users to change this behaviour. Setting protocol = pickle.HIGHEST_PROTOCOL or protocol = -1, tells pickle to use the fastest, most memory efficient option available. By using the highest protocol, you can save files that take up as much space as a netcdf or .mat file containing the same data.

• Earle briefly showed how to make a plot with broken axes. An example is given here.

• We had a pretty lengthy discussion about version control software - git, in particular. JPaul brought up the git rebase command and showed how it can be useful when pushing changes to a group repository. We also tried to understand the difference between git checkout and git reset. Cim mentioned that bitbucket is an alternative to github and offers free, online private repositories.

• Jake says that PyHOG (PYthon Hour for Oceanographers and Geoscientists) sounds a lot better than GeoPUG (Geoscience Python User Group). So, PyHOG it is...

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