# Python: Variables

### Thursday 20th July 2017 12:40pm

In mathematics variables store numerical values and are usually assigned a single letter for example **E=MC****²**. This formula states that energy (**E**) equals mass (**M**) multiplied by the speed of light (**C**) squared. When writing programs developers can use variables of any length allowing for more descriptive names; when assigning a value to a variable we use the = (equal sign). When choosing a name for your variable there are recommended coding conventions; these are outlined in PEP8. Choose clear, concise lower-case names with _ (underscores) to seperate different words.

The above equation could use variable names like **energy** = ((**mass** * **speed**)**2):

mass = 1 # Mass (kilograms) speed = 299792458 # Speed of light (metres per second) energy = ((mass * speed) ** 2) # Energy (joules)

Output:

>>> print energy 89875517873681764

Variables can also store values of different data types i.e. numbers, text, lists etc.:

>>> age = 42 >>> greeting = "Hello World!" >>> parent_names = ["Brian Damage", "Emma Nutter"]