Writing backwards compatible code

[Steven D'Aprano]

I came across an interesting (as in the Chinese curse) problem today. I
had to modify a piece of code using generator expressions written with
Python 2.4 in mind to run under version 2.3, but I wanted the code to
continue to use the generator expression if possible.

My first approach was to use a try...except block to test for generator
expressions:

try:
    gen = (something for x in blah)
except SyntaxError:
    def g():
        for x in blah:
            yield something
    gen = g()


This failed to work under 2.3, because the SyntaxError occurs at compile
time, and so the try block never happens.

I've been burnt by making assumptions before, so I tried a second,
similar, approach:

if sys.version_info >= (2, 4):
    gen = (something for x in blah)
else:
    # you know the rest

As expected, that failed too.

The solution which worked was to put the generator expression in a second
module, then import that:

try:
    import othermodule
except SyntaxError:
    # fall back code


What techniques do others use?


-- 
Steven.