# Python: Function Signature

The `pow()`

function calculates a number to a given power. It takes two parameters: **the number** and **the power**. If you call `pow()`

without parameters, Python outputs the following: `"TypeError: pow expected at least 2 arguments, got 0. The interpreter tells you that the function expects two parameters and you called it without them.

The `pow()`

function always has two mandatory parameters, so it cannot be called with any other number of parameters.

Moreover, the parameters of `pow()`

can only be numbers. For example, if you pass a couple of lines into it, it will result in the following error: `"TypeError: unsupported operand type(s) for ** or pow(): 'str' and 'str'"`

. The result of a function call is also always a number.

Other functions can have different amounts and types of parameters. For example, there may be a function that takes three parameters: a number, a string, and another number.

To know these details about a particular function, you have to look at its **signature**. It defines the input parameters and their types, as well as the output parameter and its type. You can read about the `pow()`

function in the official Python documentation. Usually the documentation for a function looks like this:

```
pow(x, y[, z])
Returns x to the power of y; if z is present, returns x to the power of y, modulus z
```

The first line here is the function signature. The function has two mandatory parameters, `x`

and `y`

. The optional parameter `z`

is given in square brackets. Next, the purpose of the function is explained. The documentation lets you know how many arguments the function has and what type they are. It also describes what the function returns and what type the return value will be.

## Instructions

Now it's your turn, look at the signature of a function in the documentation and work out how to use it.

Python has a function called `hex()`

. Study its signature here.

Write a program that uses the `hex()`

function with the variable `number`

and displays the result on the screen.

## The exercise doesn't pass checking. What to do? 😶

If you've reached a deadlock it's time to ask your question in the «Discussions». How ask a question correctly:

- Be sure to attach the test output, without it it's almost impossible to figure out what went wrong, even if you show your code. It's complicated for developers to execute code in their heads, but having a mistake before their eyes most probably will be helpful.

## In my environment the code works, but not here 🤨

Tests are designed so that they test the solution in different ways and against different data. Often the solution works with one kind of input data but doesn't work with others. Check the «Tests» tab to figure this out, you can find hints at the error output.

## My code is different from the teacher's one 🤔

It's fine. 🙆 One task in programming can be solved in many different ways. If your code passed all tests, it complies with the task conditions.

In some rare cases, the solution may be adjusted to the tests, but this can be seen immediately.

## I've read the lessons but nothing is clear 🙄

It's hard to make educational materials that will suit everyone. We do our best but there is always something to improve. If you see a material that is not clear to you, describe the problem in “Discussions”. It will be great if you'll write unclear points in the question form. Usually, we need a few days for corrections.

By the way, you can participate in courses improvement. There is a link below to the lessons course code which you can edit right in your browser.

## Definitions

Function Signature a formal description of the types of arguments and the type of the function's return value.