Python Learning Note 7: Function objects and function objects as parameters

First, the lambda function
Like what:

Fun1 = lambda x,y:x + yprint fun1 (3,4)

Output: 7

Lambda generates a function object. The function is x, Y, and the return value is x+y. The function object is assigned to Func.
The invocation of Func is the same as a normal function.

The above code is equivalent to:

def fun2 (x, y):    return x + y

Second, function as the number of parameters
function can act as an object. To pass the number of parameters.
Like what:

Fun = lambda x, Y:x+ydef runfun (fun, A, b): "Print Fun"    (b) runfun (fun, 3, 5)

Output: 8

Another example:

Runfun ((lambda x,y:x**2 + y), 6, 9)

C. Map () function
Map () is a python built-in function. Its first parameter is a function object.

The function of map () is to apply function objects to each element of the table in turn. and returns the result.

Such as:

Ret1 = Map ((lambda x:x+1), []) Print Ret1ret2 = map (lambda x,y:x+y), [1,2,3],[10,100,1000]) print Ret2

Output:

[2, 3, 4] [11, 102, 1003]

Third, filter () function
The first parameter of the filter function is also a function object. It is also the function object that will act as a parameter to multiple elements.
Assuming that the function object returns True, the elements of that secondary are stored in the returned table. Filter filters the data by a function that is read in.
Such as:

Def fun3 (a):    if a >:        return True    else:        return falseprint filter (FUN3, [10,20,100,110])

Output: [+]


Four, reduce () function
The first parameter of the reduce function is also a function, but there is a requirement that the function itself can receive two of the parameters.

Like what:

Print reduce ((lambda x,y:x+y), [1,2,3,4,5])

Output: the

Reduce passes the first two elements (1 and 2) in a table to a lambda function, resulting in 3.

The return value (3) is used as the first parameter of the lambda function, and the next element in the table (3) acts as the second parameter of the lambda function, making the next call to the lambda function, resulting in 6.

Call the lambda function in turn. The first parameter of each lambda function is the result of the previous operation, and the second is the next element in the table, until there are no remaining elements in the table.

The example above. Equivalent (((1+2) +3) +4) +5


Note: In the 3.x version number map,filter,reduce These three functions are slightly different

Python Learning Note 7: Function objects and function objects as parameters