define-range.md

define-range

The define-range is a simple one - the orignal python2 range() was actually creating a temporary object containing all the numbers requested in the range-call. However it was found that nobody really needed any list-object call - only the elements were used in an iteration loop. So when the generator-yield syntax came about, python2 introduced xrange() returning an Iterator.

In python3 the range() call returns the Iterator. That's an unfortunate choice (they should have justed dropped range() an kept xrange()). When first writing code compatible for python2 and python3, it may be handy to write with xrange() and make a define xrange = range when running in python3 mode. However this transformer does the opposite - it defaults to the python3 range() Iterator and overrides python2 range() with its own xrange() Iterator. Yes, overriding bultin functions is allowed.

    # original
    def foo(x: int):
        for i in range(x):
           print(i)
    
    # transformed
    import sys
    if sys.version_info < (3, 0):
        range = xrange
        
    def foo(x: int):
        for i in range(x):
           print(i)

Note that if a --python-version of 3.0 or later is selected then this transformer will not be executed at all.