lundi 20 septembre 2010

Quick function definition: lambda and "closure"

There is 2 ways to define a function in Python. The classical:
def fitfunc(p,x):
         return p[0]*exp(-(x-p[1])**2/(2.0*p[2]**2))
and with the use of lambda:
fitfunc = lambda p, x: p[0]*exp(-(x-p[1])**2/(2.0*p[2]**2))

Both can be used in any place:

From what I saw on the net, the compact lambda definition is more used when the function is small and used locally...

BTW, while Googling around this concept, I found this:

In [114]: def summer(nombre):
   .....:     def sumit(value):
   .....:         return value+nombre
   .....:     return sumit
In [115]: sum10 = summer(10)

In [116]: sum10(20)
Out[116]: 30

The summer function return a function, which depend on the value of the nombre variable. And the sum10 function keep in mind the value 10, even after leaving the summer function. This is what the computing science people name a "closure"...

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