Types

We’ve seen a number of different types of values so far, let’s review them:

Integers (int)

>>> 23
23
>>> 45
45
>>> 69
69
>>> 2**20
1048576
>>> -2**20
-1048576
>>> 10**100 # a googol as an integer
10000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000

Integers are “whole numbers” just as you learned in school. The can be positive or negative and (in python) can be arbitrarily large, though your computer might run out of memory trying to think about some of them.

We can enter integers in different formats too:

>>> 0x10
16
>>> 0x20
32
>>> 0x21
33
>>> 0x9
9
>>> 0xa
10
>>> 0xb
11
>>> 0o10
8
>>> 0o20
16
>>> 0o77
63
>>> 0o70
56

Floats (float)

>>> 23.0
23.0
>>> 45.0
45.0
>>> -39.
-39.0
>>> 1e100 # a googol in scientific notation
1e+100

Floating point numbers are a way of representing numbers-with-fractions in a computer. Behind the scenes they are actually an approximation of the binary fraction closest to the number you are trying to represent. So a fraction that is exactly 1/2, 1/4, 1/8, 1/16, 1/32, etc will be precisely represented, but any other fraction will be an approximation of the value.

>>> .5
0.5
>>> .25
0.25
>>> 1/3
0.3333333333333333
>>> f'%0.30f'%(1/3)
'0.333333333333333314829616256247'

Strings (str)

>>> "this"
'this'
>>> 'that'
'that'

Strings, internally, are a sequence of code points which represent the characters in the text. There are a large number of different ways that computers encode and decode text (called encodings). So when a program wants to read or write text to a file or the network, the string will be turned from the internal representation (called unicode) to the external representation (called binary or bytes).

We can add characters to strings that are otherwise hard type type by using an escape code which is a back-slash character \ followed by a special character (for common codes) or the numeric code-point of the character.

>>> '\u27a2'
'➢'
>>> '\n'
'\n'
>>> print('\ta\tb') 
        a       b

Booleans (bool)

>>> True
True
>>> False
False

Exercise

>>> type(0)
<class 'int'>

• Explore the types for other data-types we’ve seen.

Note

What do those () characters mean in type(0)?

We are asking a “thing” called type to “act” upon a single thing, which is our integer value 0. The thing type has a piece of code (a “function” or “method”) that tells it what to do when it is “asked to act” (“called”) on a set of things (“arguments” or “parameters”). Here the set of arguments we are passing is a single value, but later on we will see how to pass multiple arguments into functions which support multiple arguments.

We’ll see how to write our own functions later in this tutorial. A “method” is a function which is “attached” to an object, we’ll use these throughout the tutorial, but this tutorial does not yet cover how to write our own objects.

Extra Exercise

• Play with type and the results of type

>>> type(4)(3.14159)
3
>>> type("this")(3.14159)
'3.14159'
>>> type(type)
<class 'type'>
>>> type(type)(type)
<class 'type'>