[Numpy-discussion] fromiter

[Tim Hochberg]

I finally got around to cleaning up and checking in fromiter. As Travis 
suggested, this version does not require that you specify count. From 
the docstring:

    fromiter(...)
        fromiter(iterable, dtype, count=-1) returns a new 1d array
    initialized from iterable. If count is nonegative, the new array
    will have count elements, otherwise it's size is determined by the
    generator.

If count is specified, it allocates the full array ahead of time. If it 
is not, it periodically reallocates space for the array, allocating 50% 
extra space each time and reallocating back to the final size at the end 
(to give realloc a chance to reclaim any extra space).

Speedwise, "fromiter(iterable, dtype, count)" is about twice as fast as 
"array(list(iterable),dtype=dtype)". Omitting count slows things down by 
about 15%; still much faster than using "array(list(...))".  It also is 
going to chew up more memory than if you include count, at least 
temporarily, but still should typically use much less than the 
"array(list(...))" approach.

-tim