Python lambda function doesn't work in correct manner

Question

I'm a noob of Python. These are my variables:

>>> y=1

>>> i=5

I use the lambda function:

>>> (lambda y: y*i)(i)

>>> 25

Why the output is 25 if y=1 and i=5???????

If I use numbers:

>>> (lambda y: 1*i)(i)

>>> 5

Is this normal? Why the y is 5 in the first case, and 1 in the other case?

Answer 1

These are actually working in correct manner. Your first lambda expressions is similar to:

def f(y):
    return y * i

As you can see y is the argument of the function. And it is returning the argument * i (whatever i's value is).

So (lambda y: y*i)(i) is like calling f(i). Now you have already set i's value as 5. So it's basically f(5) and returning you the value (5 * 5) -> 25.

The second expression is similar to:

def g(y):
     return 1 * y

You are passing i in g(). i's value is 5, So it's like calling g(5) and it's returning you the value (1 * 5) -> 5 .

Answer 2

You've passed i as the first argument. This means that y in the lambda is bound to the value in i. And then you multiply y by i. This results in 5 * 5, or 25.