G3Timestream Slicing

[jlashner]

Slicing of G3Timetreams in python differs a bit from np.array slicing.

In python you are allowed to slice lists with stop and step being larger than the size of the array:

>>> import numpy as np
>>> x = np.arange(5.)
>>> x[:10]
array([0., 1., 2., 3., 4.])
>>> x[::10]
array([0.])

However G3Timestreams produce fatal errors when trying the same thing:

>>> from spt3g import core
>>> import numpy as np
>>> x = core.G3Timestream(np.arange(5.))
>>> x[:10]
FATAL (G3Timestream): Stop index 10 out of range (G3Timestream.cxx:822 in G3TimestreamPtr {anonymous}::G3Timestream_getslice(const G3Timestream&, boost::python::slice))
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/mnt/so1/shared/software/spt3g_software/200627/build/spt3g/core/timestreamextensions.py", line 13, in G3Timestream_getitem
    it = x._cxxslice(y)
RuntimeError: Stop index 10 out of range (in G3TimestreamPtr {anonymous}::G3Timestream_getslice(const G3Timestream&, boost::python::slice))
>>> x[::10]
FATAL (G3Timestream): Step index 10 out of range (G3Timestream.cxx:824 in G3TimestreamPtr {anonymous}::G3Timestream_getslice(const G3Timestream&, boost::python::slice))
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/mnt/so1/shared/software/spt3g_software/200627/build/spt3g/core/timestreamextensions.py", line 13, in G3Timestream_getitem
    it = x._cxxslice(y)
RuntimeError: Step index 10 out of range (in G3TimestreamPtr {anonymous}::G3Timestream_getslice(const G3Timestream&, boost::python::slice))

It would be great if we could change G3Timestream so slicing behavior is consistent with numpy arrays.