On Thu, 12 May 2005, Bernard Lebel wrote:
> Just a generic question: why one would use apply()?
>
> In Learning Python, on page 357, there is an example of generating an
> instance using apply():
>
> class A:
> def __init__( self, number ):
> self.number = number
>
> a = apply( A, 3 )
>
> What is the benefit of doing this over simply creating an instance
> "the usual way":
>
> a = A( 3 )
Hi Bernard,
Just wanted to mention that Python allows us to define functions that take
a variable number of arguments:
######
>>> max(1, 2, 3, 4, 5)
5
>>> def mymax(*things):
... biggest = things[0]
... for x in things:
... if x > biggest:
... biggest = x
... return biggest
...
>>> mymax("this", "is", "a", "test")
'this'
######
So this 'mymax' function can take in an arbitrary number of arguments.
This power comes with a slightly nonobvious problem: let's say that we had
a list of things:
######
>>> words = """hello world this is a test of the emergency broadcast
... system""".split()
######
Can we call mymax() to get the maximum word in this list?
We might try to brute-force this:
mymax(words[0], words[1], words[2], ...)
but there is a better approach:
apply(mymax, words)
In newer versions of Python, we have syntactic sugar to make it easier to
say: "Apply this function with the elements of the input list":
mymax(*words)
So apply (and the * stuff) really come into play when we're doing
functions with variable number of arguments. Hope this helps!
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