First, the lambda function
For example:
Fun1 = lambda x,y:x + yprint fun1 (3,4)
Output:
7
Lambda generates a function object. The function parameter 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 a parameter
Functions can be used as an object for parameter passing.
For example:
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 argument is a function object.
The function of map () is to apply the function object to each element of the table sequentially, and return 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 a function object that will act as a parameter to multiple elements.
If 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 parameters.
For example:
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, each time the first parameter of the lambda function is the result of the last operation, and the second argument is the next element in the table, until there are no remaining elements in the table.
The above example, equivalent (((1+2) +3) +4) +5
Note: In the 3.x version map,filter,reduce these three functions are slightly different
Python Learning Note 7: Function objects and function objects as parameters
