It seems that flex arrays do not support slice assignment:

py> from scitbx.array_family import flex

py> ary = flex.float(range(5))

[0.0, 1.0, 2.0, 3.0, 4.0]

py> ary[:3] = flex.float([41, 42, 43])

---------------------------------------------------------------------------

ArgumentError Traceback (most recent call last)

/usr/local/cctbx/cctbx_sources/mmtbx/dynamics/<ipython-input-13-5ce3d648bc6f> in <module>()

----> 1 ary[:3] = flex.float([41, 42, 43])

ArgumentError: Python argument types in

float.__setitem__(float, slice, float)

did not match C++ signature:

__setitem__(scitbx::af::versa<float, scitbx::af::flex_grid<scitbx::af::small<long, 10ul> > > {lvalue}, scitbx::af::small<long, 10ul>, float)

__setitem__(scitbx::af::versa<float, scitbx::af::flex_grid<scitbx::af::small<long, 10ul> > > {lvalue}, long, float)

Slice assignment is common in python:

py> alist = range(5)

py> alist[:3] = [41, 42, 43]

Is there a flex array work-alike for this operation?

I've found set_selected():

py> sel_ary = flex.bool([True, True, True, False, False])

py> ary.set_selected(sel_ary, flex.float([41, 42, 43]))

<scitbx_array_family_flex_ext.float at 0x101df1158>

[41.0, 42.0, 43.0, 3.0, 4.0]

But set_selected() is cumbersome for slice assignment because (1) you have to build a flex selection array somehow and (2) you have to put the new values into a flex array of the appropriate type. Is set_selected() the best way? If so, is there something in the cctbx libraries that makes building "slicing" selection arrays more efficient than say a list comprehension?

sel_ary = flex.bool([True if i < 3 else False for i in xrange(5)])