Introduction to the math module: pi and sqrt()

The math module

We鈥檝e seen that Python provides us with quite a few conveniences 鈥渞ight out of the box.鈥� Among these are built-in functions, that we as programmers can use鈥攁nd reuse鈥攊n our code with little effort. For example, print(), and there are many others.

We鈥檝e also learned about how to define constants in Python. For example, Newton鈥檚 gravitational constant:

G = 6.67 * 10 ** -11  # N m^2 / kg^2

Here we鈥檒l learn a little about 笔测迟丑辞苍鈥檚 math module. The Python math module is a collection of constants and functions that you can use in your own programs鈥攁nd these are very, very convenient. For example, why write your own function to find the principal square root of a number when Python can do it for you?¹

Unlike built-in functions, in order to use functions (and constants) provided by the Python math module, we must first import the module (or portions thereof).² You can think of this as importing features you need into your program.

笔测迟丑辞苍鈥檚 math module is rich with features. It provides many functions including

function	calculation
sqrt(x)	\sqrt{x}
exp(x)	e^x
log(x)	\ln x
log2(x)	\log_2 x
sin(x)	\sin x
cos(x)	\cos x

and many others.

Using the math module

To import a module, we use the import keyword. Imports should appear in your code immediately after the starting docstring, and you only need to import a module once. If the import is successful, then the imported module becomes available.

>>> import math

Now what? Say we鈥檇 like to use the sqrt() function provided by the math module. How do we access it?

If we want to access functions (or constants) within the math module we use the . operator.

>>> import math
>>> math.sqrt(25)
5.0

Let鈥檚 unpack this. Within the math module, there鈥檚 a function named sqrt(). Writing math.sqrt() is accessing the sqrt() function within the math module. This uses what is called dot notation in Python (and many other languages use this as well).

Let鈥檚 try another function in the math module, sin(), which calculates the sine of an angle. You may remember from pre-calculus or trigonometry course that \sin 0 = 0, \sin \frac{\pi}{2} = 1, \sin \pi = 0, \sin \frac{3\pi}{2} = -1, and \sin 2\pi = 0. Let鈥檚 try this out.

>>> import math
>>> PI = 3.14159
>>> math.sin(0)
0.0

So far, so good.

>>> math.sin(PI / 2)
0.999999998926914

That鈥檚 close, but not quite right. What went wrong? (Hint: Representation error is not the problem.) Our approximation of \pi (defined as PI = 3.14159, above) isn鈥檛 of sufficient precision. Fortunately, the math module includes high-precision constants for \pi and e.

>>> math.sin(math.pi / 2)
1.0

Much better.

It is left to the reader to test other arguments to the sin() function.

math module documentation

As noted, the math module has many ready-made functions you can use. For more information, see the math module documentation.

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Copyright 漏 2023鈥�2025 Clayton Cafiero

No generative AI was used in producing this material. This was written the old-fashioned way.

Footnotes

1. The only reasonable answer to this question is 鈥渇or pedagogical purposes鈥�, and in fact, later on, we鈥檒l do just that鈥攚rite our own function to find the principal square root of a number. But let鈥檚 set that aside for now.

2. We鈥檙e going to ignore the possibility of importing portions of a module for now.