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# Sort tuples, and lambda usecase

```
my_list.sort(key=lambda x: x[1])
```

`key` is a function that will be called to transform the collection's items before they are compared. The parameter passed to `key` must be something that is callable.

The use of `lambda` creates an anonymous function (which is callable). In the case of `sorted` the callable only takes one parameters. Python's `lambda` is pretty simple. It can only do and return one thing really.

The syntax of `lambda` is the word `lambda` followed by the list of parameter names then a single block of code. The parameter list and code block are delineated by colon. This is similar to other constructs in python as well such as `while`, `for`, `if` and so on. They are all statements that typically have a code block. Lambda is just another instance of a statement with a code block.

We can compare the use of lambda with that of def to create a function.

```
adder_lambda = lambda parameter1,parameter2: parameter1+parameter2
def adder_regular(parameter1, parameter2): return parameter1+parameter2
```

lambda just gives us a way of doing this without assigning a name. Which makes it great for using as a parameter to a function.

`variable` is used twice here because on the left hand of the colon it is the name of a parameter and on the right hand side it is being used in the code block to compute something.