And if you're interested, the name "lambda" itself comes from lambda calculus: http://en.wikipedia.org/wiki/Lambda_calculus http://en.wikipedia.org/wiki/Lambda_calculus#First-class_functions http://en.wikipedia.org/wiki/Anonymous_functions
On Tuesday, December 21, 2010 4:02:36 PM UTC-5, stefaan wrote: > pbreit wrote: > > I see lambda used quite a bit and don't totally understand the concept. > > Is there a simple rule to follow to know when it is necessary to use? > > Sometimes you need to pass a function as an argument to another > function. In that case you have a choice to > > 1. define a separate function, and pass that to the function you are > calling: > > def my_fun(x, y, operation): > return operation(x, y) > > The function my_fun takes two numbers x and y, and one function > "operation" that is applied to x and y > > You can e.g. use it as follows to perform an addition: > > def my_addition(x, y): > return x+y > > >>> print my_fun(1, 2, my_addition) > 3 > > 2. you can omit defining the separate function "my_addition" and pass in > an anonymous function (defined using lambda) instead: > > def my_fun(x, y, operation): > return operation(x,y) > > >>> print my_fun(1,2, lambda x,y : x+y) > 3 > > So lambda is used to define a function on-the-spot, without even > bothering to give it a name of its own (an "anonymous" function). The > "lambda x,y" part tells the system that you define an anonymous function > expecting two arguments named x and y. The x+y part tells the system > that the anonymous function returns the sum of its x and y arguments. > > Hope this helps, > Best regards, > Stefaan. > >
