Types

We have already seen that there are various types of data availabe in Python. Thus far, we have categorised our data in a very simple manner: numbers and letters. In reality, the situation is slightly more nuanced than this and it is worth being aware of all of the basic data types that you can play with.

Numeric types

Python provides an built-in function for determining the type of some data. For example:

type(2)

int

Here, we call the type function on the number \(3\), and Python informs us that this data is of type int: it is an integer. What if we try a number which is not an integer?

type(3.5)

float

As referenced earlier, numbers with a decimal point are floats, Python tells us as much in the code above. There is also a third basic numeric type:

type(3 + 2j)

complex

The complex data type represents complex numbers. The j in the code above represents the imaginary component which is usually written with an “i” on pen and paper: \(3 + 2i\). For the purposes of this course, it is very unlikely that you will need to manipulate complex data, but it is worth noting that Python does have this capability.

It has not been explicitly highlighted before, but Python will automatically change an int to a float if necessary:

an_integer = 5
a_float = 2.2

sum_of_two_numbers = an_integer + a_float
print(sum_of_two_numbers)

type(sum_of_two_numbers)

7.2

float

In this example, we are adding a float to an int which means that the result must also be a float.

Strings

Strings are clearly very different from the numeric data discussed above; this is reflected by the type function:

type("Look at me, I'm a string!")

str

Hopefully this further clarifies some of the examples you were asked to work through in the Strings exercise:

an_integer = 7
a_string = 'Strings are not numbers!'

an_integer + a_string

---------------------------------------------------------------------------
TypeError                                 Traceback (most recent call last)
Cell In[6], line 4
      1 an_integer = 7
      2 a_string = 'Strings are not numbers!'
----> 4 an_integer + a_string

TypeError: unsupported operand type(s) for +: 'int' and 'str'

Error

This code yields a TypeError, which means that we are trying to operate on different data types in a way that doesn’t make any sense. Here we are trying to “add” an int (integer) to a str(string): it is unclear how we might do this.

Of course, there are situations in which we might want to add an integer to a string. Consider the following:

'This is an integer: ' + 10

This code will raise an error much like the previous example, but as human beings we can see how it might make some sense. To add the int to the str, we have to cast it to a str:

an_integer = 10
a_string = 'This is an integer: '

a_string + str(an_integer)

'This is an integer: 10'

Here we have used the in-built str function to cast the int to a str. In other words, we have converted the type of an_integer and turned it into a string. This process is, in a simplified manner, what happens automatically when we use f-strings with numbers: the relevant variable is formatted into a string:

an_integer = 10

f'This is an integer: {an_integer}'

'This is an integer: 10'

Booleans

The final basic data type we have yet to cover is the Boolean. This type of data represents two possible logical values: True or False:

type(True)

bool

type(False)

bool

We have yet to see how this type of data can be useful, but we will come to this in due course. True and False are the first reserved keywords that we have come across: we cannot create variables with these names.

True = 5

  Cell In[16], line 1
    True = 5
    ^
SyntaxError: cannot assign to True

False = 'this will raise a SyntaxError!'

  Cell In[17], line 1
    False = 'this will raise a SyntaxError!'
    ^
SyntaxError: cannot assign to False