3.1.8. Variables and Constants

3.1.8.1. Variables

  • Placeholders for important values

  • Make program more efficient

  • Make program more understandable

3.1.8.1.1. Variable Names

  • Letters, numbers, underscore

  • Starts with letter or underscore

  • Case sensitive

3.1.8.1.1.1. Good Names

  • Variable names should be descriptive

  • Python convention is to join multiple words with underscore in variable names, e.g. favorite_number = 18

3.1.8.1.1.2. Bad Names

  • Variables cannot start with a number, e.g. 1337ninja

  • Don’t use keywords as variables (names that change colour), e.g. min, max, int, print, import

  • Avoid too longer a name

3.1.8.1.2. More examples of variables

my_name = "joe warren"
print my_name

joe warren

my_age = 51
print my_age

51

#the story of the magic pill
magic_pill = 30
print my_age - magic_pill

my_granddad = 74

print my_granddad - 2 * magic_pill

21
14

#Temperature example

temp_fahrenheit = 212
temp_celcius = 5.0 / 9.0 * (temp_fahrenheit - 32)
print temp_celcius # 0degC = 32degF and 100degC = 212degF

100.0

temp_celcius = 100
temp_fahrenheit = 9.0 / 5.0 * temp_celcius + 32
print temp_fahrenheit # 0degC = 32degF and 100degC = 212degF

212.0

3.1.8.2. Constants

Python has no constants, just use capital letters, e.g.

ACCELERATION_G = 9.81
TRUCK_MASS = 10000
WATER_VISCOSITY = 10**-3