Q:

Discovering keys using h5py in python3

In python2.7, I can analyze an hdf5 files keys use
$ python
>>> import h5py
>>> f = h5py.File('example.h5', 'r')
>>> f.keys()
[u'some_key']

However, in python3.4, I get something different:
$ python3 -q
>>> import h5py
>>> f = h5py.File('example.h5', 'r')
>>> f.keys()
KeysViewWithLock(<HDF5 file "example.h5" (mode r)>)

What is KeysViewWithLock, and how can I examine my HDF5 keys in Python3?

A:

From h5py's website (http://docs.h5py.org/en/latest/high/group.html#dict-interface-and-links):

When using h5py from Python 3, the keys(), values() and items()
  methods will return view-like objects instead of lists. These objects
  support containership testing and iteration, but can’t be sliced like
  lists.

This explains why we can't view them. The simplest answer is to convert them to a list:
>>> list(for.keys())

Unfortunately, I run things in iPython, and it uses the command 'l'. That means that approach won't work.
In order to actually view them, we need to take advantage of containership testing and iteration. Containership testing means we'd have to already know the keys, so that's out. Fortunately, it's simple to use iteration:
>>> [key for key in f.keys()]
['mins', 'rects_x', 'rects_y']

I've created a simple function that does this automatically:
def keys(f):
    return [key for key in f.keys()]

Then you get:
>>> keys(f)
['mins', 'rects_x', 'rects_y']

