Tuesday, December 05, 2006

Statement Functions

At a small suggestion in #python, I wrote up a simple module that allows the use of many python statements in places requiring statements. This post serves as the announcement and documentation. You can find the release here.

The pattern is the statement's keyword appended with a single underscore, so the first, of course, is print_. The example writes 'some+text' to an IOString for a URL query string. This mostly follows what it seems the print function will be in py3k.

print_("some", "text", outfile=query_iostring, sep="+", end="")

An obvious second choice was to wrap if statements. They take a condition value, and expect a truth value or callback an an optional else value or callback. Values and callbacks are named if_true, cb_true, if_false, and cb_false.

if_(raw_input("Continue?")=="Y", cb_true=play_game, cb_false=quit)

Of course, often your else might be an error case, so raising an exception could be useful.

raise_(TypeError("Wrong datatype!"))

When you do have exceptions, you often want to handle them and we can even do this in expressions now. Maybe we just want to report the error. The try_ function takes keywords for except_, else_, and finally_ callbacks. All take exception type, exception, and traceback arguments, with else_ and _finally also taking first arguments as the result of the attempted callable.

try_(some_func, except_=lambda e,et,tb:print_(et, ':', e))

Errors also can come from failed assertions.

assert_(lambda: True == False)

Loops are also supported. for_ is mostly like map, but it also takes an else_ argument which is called with the last value from the iterator. while_ takes a condition callable, either a for_each callable or an iterator. The condition is given the result of the last loop.

for_("abc", print_, lambda i: print_("done"))

while_(lambda last:last<99, xrange(100), lambda_ i: print_("done"))

Finally, some simple ones:

pass_(10, foo="a") # returns ((10,), {'foo': 'a'})

exec_("a = b", globals(), locals())

I don't recommend using this a whole lot, but in the cases its useful, enjoy.

1 comment:

bobuk said...

Wow! Nice-nice-nice!

But in if_ you need to rename callbacks from cb_true to then_ and from cb_false to else_!

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