# Lesson 12 - Importing modules and the math module in Python

In the previous lesson, Tuples, sets, and dictionaries in Python, we learned about multi-dimensional lists
in Python. In today's tutorial, we're going to learn to use libraries. Mainly,
the `math`

library.

## Libraries

Libraries (or modules) provides us with useful data types, functions, and tools for making even better programs. They're made so we don't have to re-write something someone else has already written for us. If we make our programs using existing modules, the development process will be much more comfortable and quick.

We import libraries using the `import`

command, **at the
beginning of our source file**.

`import module_name`

Then, we call module functions as they were in the module's methods:

module_name.function_name()

We can also choose to only import certain functions:

from module_name import function_name

Then, the function would be globally accessible:

function_name()

We could even make everything from the module be accessible globally. However, be careful with this approach and use it only if you know exactly what you're doing:

from module_name import *

`math`

First, let's introduce you to the Python math module - `math`

. We
have to import it in order to use it:

#!/usr/bin/python3 import math

The module provides 2 fundamental constants for us: `pi`

and
`e`

. `pi`

, as you all know, is the number Pi
(`3.1415...`

), and `e`

is Euler's number, the base of the
natural logarithm (`2.7182...`

). I'm sure you'll get how to work with
them. For completeness' sake, let's print these constants to the console:

```
{PYTHON}
import math
print("Pi: %f" % (math.pi))
print("e: %f" % (math.e))
```

The result:

Console application Pi: 3.141593 e: 2.718282

As you can see, we can call everything from the `math`

module.

`math`

module methods

Now, let's go over the methods that the math module provides.

`ceil()`

, `floor()`

, and `random()`

All of these functions are related to rounding. `ceil()`

always
rounds upwards and `floor()`

rounds downwards no matter what. If you
just need ordinary rounding, use the global `round()`

function which
takes a decimal number as a parameter and returns the rounded number **as
a double data type** in the way we learned in school (from
`0.5`

it rounds upwards, otherwise downwards). The
`round()`

function is from the standard set of functions and isn't
dependent on the `math`

module.

We'll certainly use `round()`

very often. I've used the other
functions for things such as determining the number of pages in a guestbook. If
we had `33`

comments and we only printed `10`

comments per
page, these comments would take up `3.3`

pages. The result must be
rounded up since we would actually need `4`

pages.

```
{PYTHON}
import math
print(round(3.1))
print(round(3.6))
print(math.ceil(3.1))
print(math.floor(3.6))
```

The output:

Console application 3 4 4 3

`fabs()`

and `abs()`

The `fabs()`

method takes a decimal (`float`

) number as
a parameter and returns its absolute value (which is always positive). We also
have the global `abs()`

function which works with integers.

```
{PYTHON}
import math
print(math.fabs(-2.2))
print(math.fabs(2.2))
print(abs(-2))
print(abs(2))
```

The output:

Console application 2.2 2.2 2 2

`sin()`

, `cos()`

, `tan()`

These classic trigonometric functions all take an angle as a
`float`

, which has to be entered in radians (not degrees if your
country uses them). To convert degrees to radians we multiply them by
`(Math.PI / 180)`

. The return value is also a `float`

.

`acos()`

, `asin()`

, `atan()`

These are inverse trigonometric (arcus, sometimes cyclometric) functions,
which return the original angle according to its trigonometric value. The
parameter is a `float`

and the returned angle is in radians (also as
a `float`

). If we wanted the angle in degrees, we'd have to divide
the radians by `(180 / Math.PI)`

.

`pow()`

and `sqrt()`

`pow()`

takes two parameters. The first is the base of the power
and the second is the exponent. If we wanted to calculate 2^{3}, the
code for it would be as follows:

```
{PYTHON}
import math
print(math.pow(2, 3))
```

`sqrt()`

is an abbreviation for SQuare RooT, which returns the
square root of the number given as a `float`

. Both functions return a
`float`

as the result.

```
{PYTHON}
import math
print(math.sqrt(12))
```

`exp()`

, `log()`

, `log2()`

,
`log10()`

`exp()`

returns Euler's number raised to the given exponent.
`log()`

returns the natural logarithm of the given number or the
logarithm of the base entered as the second parameter. `log10()`

returns the decadic logarithm of the number and `log2()`

returns the
binary logarithm.

```
{PYTHON}
import math
print(math.log(16, 4))
print(math.log10(1000))
print(math.log2(32))
```

The output:

Console application 2.0 3.0 5.0

Hopefully, you noticed that the method list lacks any general root function.
We, however, can calculate it using the functions the `math`

module
provides.

We know that roots work like this: the 3rd root of `8 = 8^(1/3)`

.
Therefore, we can write the following bit of code:

```
{PYTHON}
import math
print(math.pow(8, (1/3)))
```

## Division

Programming languages often differ in how they perform the division of numbers. You need to be aware of these issues to avoid being, unpleasantly, surprised afterwards. Let's write a simple program:

```
{PYTHON}
a = 5 / 2
b = 5.0 / 2
c = 5 / 2.0
d = 5.0 / 2.0
e = 5 // 2
f = 5.0 // 2
g = 5 // 2.0
h = 5.0 // 2.0
print(a)
print(b)
print(c)
print(d)
print(e)
print(f)
print(g)
print(h)
```

We divide `5 / 2`

several times in the code. Mathematically, it's
`2.5`

. Nonetheless, the results will not be the same in all cases.
Can you guess what we'll get in each case? Go ahead, give it a try

The program output will be the following:

Console application 2.5 2.5 2.5 2.5 2 2.0 2.0 2.0

We see the result of division using the `/`

operator is always
decimal (`float`

). It doesn't really matter what the data type of the
variable we're assigning the result to is. If we wanted to perform whole-number
division, we'd have to use the `//`

operator. As you can see, it
returns decimal numbers for decimal inputs, but the value is always a whole
number (`.0`

).

### The remainder after division

In our applications, we often need the remainder after integer division (i.e.
modulo). In our example `5 // 2`

, the integer result is
`2`

and modulo is `1`

(what's left over). Modulo is often
used to determine whether a number is even (remainder of division by
`2`

is `0`

). You would use it, for example, to draw a
checkerboard and fill in the fields based on whether they are even or odd,
calculate the deviance of your position in a square grid, and so on.

In Python, as in C-like languages in general, modulo is a percent sign, i.e.
`%`

:

```
{PYTHON}
print(5 % 2) # prints 1
```

Well, that's all I've got for today. In the next lesson, Solved tasks for Python lessons 10-12, we'll learn to declare custom functions and to decompose our programs into multiple logical parts.

In the following exercise, Solved tasks for Python lessons 10-12, we're gonna practice our knowledge from previous lessons.

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