Variables

• We created a variable, but what are variables?

• They are names that point to values

• We can change the value to which they point

>>> dogs = 2
>>> cats = 1
>>> dogs
2
>>> cats
1
>>> dogs > cats
True
>>> dogs = 1
>>> dogs > cats
False
>>> dogs = 3
>>> dogs
3
>>> dogs > cats
True
>>> cats + dogs
4

We can change which thing the variable points to by reassigning the variable. Some languages have very complex rules about assignment but for Python any object can be referenced by any variable.

>>> count = 5
>>> count = 8
>>> count
8
>>> count = 'hello'
>>> count
'hello'
>>> count = count + ' world'
>>> count
'hello world'
>>> other = count
>>> count = 42
>>> other
'hello world'
>>> count
42
>>> other,count = count,other
>>> count
'hello world'
>>> other
42

Exercise

• Create a number of variables and compare them in your interpreter.

• What type of names work as variables? Can you include spaces or punctuation?

• What is the difference between = and ==?

• Should we have named our variables dog_count and cat_count?

Extra Exercise

• What should the following print? (Try to answer without running it)

>>> a,b = 1,2
>>> b,a = a,b
>>> c,b = a,b
>>> b,b = b,c
>>> print(b)