First of all, the test can be optimized by adding a boolean flag which
indicates if the data has been initialized or not, and then just
testing a boolean value instead of doing an "is" comparison, at the
cost of an extra global variable. But this is still ugly (actually
uglier IMO).
I think this is a more Pythonic way to do it.
This class implements a function which initializes itself upon the
first call:
class InitializingFunction(object):
def __init__(self, init):
def initializer(*args, **kw):
self.func = init()
return self(*args, **kw)
self.func = initializer
def __call__(self, *args, **kw):
return self.func(*args, **kw)
Now you can write your function almost exactly like you did before:
def init():
data = somethingcomplexandcostly()
def foo(a):
return simple(data, a)
return foo
func = InitializingFunction(init)
What have we gained from this? Two major advantages:
* no ugly 'global' statement
* no reliance on the function's name
And now you can easily create such functions forever using this class
to abstract away the ugly implementation ;)
Notice that since Function Decorators were introduced in Python2.4, you
can use InitializingFunction as a Decorator to achieve the same effect,
this time even without the need for a temporary name for a function:
@InitializingFunction
def func():
data = somethingcomplexandcostly()
def foo(a):
return simple(data, a)
return foo
And finally I must note that no matter which way you turn this around,
it will still be hard to read!
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