Question: I want to know what exactly is `lambda` in python? and where and why it is used.
thanks

Answer: 
The first linked returned by googling "python lambda" points to a [page](http://www.secnetix.de/olli/Python/lambda_functions.hawk) whose first paragraphs answer your question. I could copy & paste the content it, but I think it's unfair :)
Lambda is an anonymous function in Python programming language, instead of bearing a def statement in the front it is simply called and written lambda.

```
def mult2(x):
    return x*2

print(mult2(2))

```

**# returns 4**

Exactly same you can do with a lambda function. 

```
lam = lambda x : x*2
print(lam(2))

```

**# returns 4**
For more details you can look up in this blog post.
<http://friendlypython.herokuapp.com/2017/1/anonymous-function-lambda/> or [here](http://friendlypython.herokuapp.com/2017/1/anonymous-function-lambda/)