Shulou(Shulou.com)06/02 Report--

This article will share with you about the common built-in high-order functions in Python. The editor thinks it is very practical, so share it with you as a reference and follow the editor to have a look.

1. What is a higher-order function?

Higher-order function: a function can be passed as an argument to another function, or the return value of a function is another function (recursive if the return value is the function itself), and one is a higher-order function.

The argument is a function:

# Parameter is function def bar (): print ("in the bar..") def foo (func): func () print ("in the foo..") foo (bar)

The return value is a function:

# the returned value is function def bar (): print ("in the bar..") def foo (func): print ("in the foo..") Return barres=foo (bar) res ()

In the above two examples, the function foo () is a high-order function. In example 1, the function bar is passed as an argument to foo, and in example 2, the function bar is used as the return value of foo.

Note: the function name (such as bar, foo)-> it is the memory address of the function; the function name + parentheses (such as bar (), foo ())-> calls the function.

two。 Higher order functions-map, filter, reduce

These three functions are all high-order functions, which are also built-in functions of Python. Next, let's take a look at the usage of these three functions and their internal principles:

2.1map function

The map function receives two parameters, a function and a sequence, and its function is to process the values in the sequence and return them to the list in turn. The return value is an iterator object-"for example:.

Its usage is shown in the figure:

Let's take a look at the mechanism of the map function:

Num=] def square (x): return x**2#map function simulation def map_test (func,iter): num_1= [] for i in iter: ret=func (I) # print (ret) num_1.append (ret) return num_1.__iter__ () # convert the list to an iterator object # map_test function print (list (map_test (square) (num)) # map function print (list (map (square,num) # of course, parameter 1 of the map function can also be an anonymous function, and parameter 2 can also be a string print (list (map_test (lambda x:x.upper (), "amanda")) print (list (map (lambda x:x.upper (), "amanda")) 2.2filter function

The filter function is also a higher-order function that receives a function and a sequence, and its main function is filtering. The return value is also an iterator object, for example:

The figure is as follows:

Let's take a look at the use of the filter function and how it works:

Names= ["Alex", "amanda", "xiaowu"] # filter function mechanism def filter_test (func,iter): names_1= [] for i in iter: if func (I): # the result of the func function passed in must be a Bool value Names_1.append (I) return names_1#filter_test function print (filter_test (lambda x:x.islower (), names)) # filter function print (list (filter (lambda x:x.islower (), names) 2.3reduce function

Reduce function is also a function whose parameter is a function, and a higher-order function of an iterative object, whose return value is a value rather than an iterator object, so it is commonly used with superposition, superposition, etc.

An example of the figure is as follows:

Examples are as follows:

# reduce function is not a built-in function, but a function in the module functools. Therefore, it is necessary to import the mechanism of the from functools import reducenums= function def reduce_test (func,array,ini=None): # ini as the cardinality if ini= = None: ret= array.pop (0) else: ret=ini for i in array: ret=func (ret,i) return ret#reduce_test function. Overlay print (reduce_test (lambda x recorder) xlu ju numsjue 100) # reduce function, overlay print (reduce (lambda x recorder x rep y jus dome 100)) Thank you for your reading! This is the end of this article on "what are the common built-in high-order functions of Python?". I hope the above content can be helpful to you, so that you can learn more knowledge. if you think the article is good, you can share it for more people to see!

Welcome to subscribe "Shulou Technology Information " to get latest news, interesting things and hot topics in the IT industry, and controls the hottest and latest Internet news, technology news and IT industry trends.