Why (lambda x: x * 99 + x)(1 ** 5 * 5) equals 500

Question

Why output of this line (lambda x: x * 99 + x) (1 ** 5 * 5) in Python is 500 while 'x' is not defined?

Answer 1

Here, (1 ** 5 * 5) is passed as an argument to a lambda function.

(lambda x: x * 99 + x)(1 ** 5 * 5)

lambda takes input as x and acts upon it. If you have any other Lambda function it'll work in the same way.

(lambda x: x.upper())('test') # will print TEST

It's just like you're creating a function with arg x.

upper = (lambda x: x.upper())
upper('test') # will print TEST

upper here is a lambda function that takes arg x and acts upon it

<function __main__.<lambda>(x)>

Answer 2

Your lambda expression (lambda x: x * 99 + x) (1 ** 5 * 5) is comprised of two parts:

1. Declaring the function:

   (lambda x: x * 99 + x)
   

   which is equivalent to declaring the custom function as:

   def func(x):
       return (x * 99 + x)
   

2. Calling the above function with argument as (1 ** 5 * 5), which is equivalent to making the function call as:

   func(1 ** 5 * 5)
   # i.e. func(5)      ## 1**5*5 => 5
   

Because 5 * 99 + 5 is equivalent to 500. That's the answer you are getting.

Answer 3

let's review your code (lambda x: x * 99 + x) (1 ** 5 * 5)
that's mean x*99+x you'r input is (1**5*5) which equals 5 that's mean x=5
so 5*99+5=500

Answer 4

Let's break this down.

A lambda is basically a function. In your case, it has one input (x) and the return statement of x * 99 + x. It is then called with (1 ** 5 * 5).

This means that (1 ** 5 * 5) is x.

You can now do the math:

1 ** 5 * 5
> 1 * 5
> 5

x * 99 + x
> 5 * 99 + x
> 500