# Chapter 3. Functions

In the context of programming, a function is a named sequence of statements that performs a computation. When you define a function, you specify the name and the sequence of statements. Later, you can “call” the function by name.

# Function Calls

We have already seen one example of a function call:

```>>> type(42)
<class 'int'>```

The name of the function is `type`. The expression in parentheses is called the argument of the function. The result, for this function, is the type of the argument.

It is common to say that a function “takes” an argument and “returns” a result. The result is also called the return value.

Python provides functions that convert values from one type to another. The `int` function takes any value and converts it to an integer, if it can, or complains otherwise:

```>>> int('32')
32
>>> int('Hello')
ValueError: invalid literal for int(): Hello```

`int` can convert floating-point values to integers, but it doesn’t round off; it chops off the fraction part:

```>>> int(3.99999)
3
>>> int(-2.3)
-2```

`float` converts integers and strings to floating-point numbers:

```>>> float(32)
32.0
>>> float('3.14159')
3.14159```

Finally, `str` converts its argument to a string:

```>>> str(32)
'32'
>>> str(3.14159)
'3.14159'```

# Math Functions

Python has a math module that provides most of the familiar mathematical functions. A module is a file that contains a collection of related functions.

Before we can use the functions in a module, we have to import it with an import statement:

`>>> import math`

This statement ...

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