Now and then I use the Python lambda. Is it so formal that it is safe to say that you can do formal lambda calculus with it? I just used it but I didn’t fully understand whether the python lambda and the lambda calculus like I read was done by Alonzo Church. I also used it in Javascript, I think. Isn’t this more common in functional languages (e.g. Haskell, Scheme/Lisp, Clojure…) and I never saw lambda in use with Java or C(++)?
Is says on this site ” a function you can pass on to another function as argument.”.
What is “lambda” code?
But how do I get used to it enough so that I can tell where to benefit from it? If I can do it in say SQL, JPQL or GQL instead, shouldn’t I prefer to do it in the query language?
Python lambda expressions are real, formal untyped λ-calculus lambda expressions.
They fit the formal definition; they can only represent one python expression, based on variables (free or otherwise) and references to other functions (abstract symbols). Python uses parenthesis in expressions too.
You use them wherever a lambda is more suitable and convenient than a full function definition. The python def functionname(argumentlist): syntax forms a statement; in Python you cannot put statements inside of expressions, only the other way around. A lambda on the other hand, is an expression, so you can use a lambda to insert a callback function inline:
map(lambda x, y: x[y+5], [(mapping1, integerkey1), (mapping2, integerkey2)])
The above example consists only of an expression. The python map() function takes, as its first argument, a callable, which is applied to each and every element in the list given by the second argument. In the above example, using a lambda expression to define that callable is much easier than using a function statement:
def mapcallback(x, y):
return x[y + 5]
map(mapcallback, [(mapping1, integerkey1), (mapping2, integerkey2)])
For the full function syntax I need to assign a name, put the function definition on separate lines, and use the return statement to return the result of the expression.
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