Anonymous function, Lambda in Python

We have gone halfway through the Python function, in this lesson you will learn about anonymous functions, also known as Lambda functions. What is Lambda jaw, how is Lambda function syntax and how to use Lambda function with specific example.

What is Lambda function in Python?

In Python, anonymous functions are functions defined without names. If functions are normally defined using the def keyword, the anonymous function is defined using the lambda keyword. For that reason, the anonymous function is also called the Lambda function.

Lambda function syntax in Python

A Lambda function in Python has the following syntax;

 lambda tham_so: bieu_thuc 

Lambda function can have many parameters but only 1 expression. Expressions will be evaluated and returned. Lambda jaw can be used wherever the function object is required.

Lambda function example in Python

This is the Lambda function example with the task of doubling the number of entries.

 nhan_doi = lambda a: a * 2 
 
 # Kết quả: 20 
 # By TipsMake.com 
 print(nhan_doi(10)) 

In this example, lambda a: a * 2 is Lambda function. a here is the parameter and a * 2 is the expression (taking into account the calculation and returning the result). This function has no name, it returns a function object - assigned a nhan_doi. We can call it as a normal function, the following command:

 nhan_doi = lambda a: a * 2 

almost like:

 def nhan_doi(a): 
  return a * 2 

Using Lambda in Python

Usually Lambda function is used when an anonymous function is needed in a short time, for example as an argument to a higher order function. Lambda function is often used with built-in Python functions such as filter () or map (), .

For example, using Lambda function with filter ():

The filter () function takes parameters as a function and a list. The function is called with all the items in the list and the new list will be returned, containing the items that the function evaluates to as True. This is an example of using the filter () function to filter out even numbers in the list.

 list_goc = [10, 9, 8, 7, 6, 1, 2, 3, 4, 5] 
 
 list_moi = list(filter(lambda a: (a%2 == 0) , list_goc)) 
 
 # Kết quả: [10, 8, 6, 2, 4] 
 # By TipsMake.com 
 print(list_moi) 

For example, using Lambda function with map ():

The map () function also takes parameters as a function and a list. The function is called with all the items in the new list and list returned containing the items returned by the corresponding function for each item. Saying it seems ambiguous, you see the following example will be much easier to understand:

 list_goc = [10, 9, 8, 7, 6, 1, 2, 3, 4, 5] 
 
 list_moi = list(map(lambda a: a*2 , list_goc)) 
 
 # Kết quả: [20, 18, 16, 14, 12, 2, 4, 6, 8, 10] 
 # By TipsMake.com 
 print(list_moi) 

Is there anything in the anonymous function that we missed? Please comment below to comment. Don't forget to do Python exercises and look forward to the next lesson.

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