Understanding Data Types

Background

One way to think about data types is to consider the different types of data that we use in the real world. An example of data in the real world are numbers: we may use whole numbers (0, 1, 2, …), integers (…, -1, 0, 1, …), and irrational numbers (π), for example.

Usually, in math, we can combine numbers from different types, and get some kind of an answer. We may want to add 5 to π, for example:

5 + π

We can either keep the equation as the answer to account for the irrational number, or round π to a number with a brief number of decimal places, and then add the numbers together:

5 + π = 5 + 3.14 = 8.14

But, if we start to try to evaluate numbers with another data type, such as words, things start to make less sense. How would we solve for the following equation?

sky + 8

For computers, each data type can be thought of as being quite different, like words and numbers, so we will have to be careful about how we use them to assign values and how we manipulate them through operations.

Numbers

Any number you enter in Python will be interpreted as a number; you are not required to declare what kind of data type you are entering. Python will consider any number written without decimals as an integer (as in 138) and any number written with decimals as a float (as in 138.0).

print(-25)

-25

my_int = -25
print(my_int)

-25

int_ans = 116 - 68
print(int_ans)

48

print(17.3)

17.3

my_flt = 17.3
print(my_flt)

17.3

flt_ans = 564.0 + 365.24
print(flt_ans)

929.24

Booleans

The Boolean data type can be one of two values, either True or False. Booleans are used to represent the truth values that are associated with the logic branch of mathematics, which informs algorithms in computer science.

Whenever you see the data type Boolean, it will start with a capitalized B because it is named for the mathematician George Boole. The values True and False will also always be with a capital T and F respectively, as they are special values in Python.

Many operations in math give us answers that evaluate to either True or False:

• greater than
  • 500 > 100 True
  • 1 > 5 False
• less than
  • 200 < 400 True
  • 4 < 2 False
• equal
  • 5 = 5 True
  • 500 = 400 False

Like with numbers, we can store a Boolean value in a variable:

my_bool = 5 > 8

We can then print the Boolean value with a call to the print() function:

print(my_bool)

Since 5 is not greater than 8, we will receive the following output:

False

As you write more programs in Python, you will become more familiar with how Booleans work and how different functions and operations evaluating to either True or False can change the course of the program.

Strings

A string is a sequence of one or more characters (letters, numbers, symbols) that can be either a constant or a variable. Strings exist within either single quotes ' or double quotes " in Python, so to create a string, enclose a sequence of characters in quotes:

'This is a string in single quotes.'

"This is a string in double quotes."

You can choose to use either single quotes or double quotes, but whichever you decide on you should be consistent within a program.

The simple program “Hello, World!” demonstrates how a string can be used in computer programming, as the characters that make up the phrase Hello, World! are a string.

print("Hello, World!")

As with other data types, we can store strings in variables:

hw = "Hello, World!"

And print out the string by calling the variable:

print(hw)

Hello, World!

Like numbers, there are many operations that we can perform on strings within our programs in order to manipulate them to achieve the results we are seeking. Strings are important for communicating information to the user, and for the user to communicate information back to the program.

Lists

A list is a mutable, or changeable, ordered sequence of elements. Each element or value that is inside of a list is called an item. Just as strings are defined as characters between quotes, lists are defined by having values between square brackets [ ].

A list of integers looks like this:

[-3, -2, -1, 0, 1, 2, 3]

A list of floats looks like this:

[3.14, 9.23, 111.11, 312.12, 1.05]

A list of strings:

['shark', 'cuttlefish', 'squid', 'mantis shrimp']

If we define our string list as sea_creatures:

sea_creatures = ['shark', 'cuttlefish', 'squid', 'mantis shrimp']

We can print them out by calling the variable:

print(sea_creatures)

And we see that the output looks exactly like the list that we created:

['shark', 'cuttlefish', 'squid', 'mantis shrimp']

Lists are a very flexible data type because they are mutable in that they can have values added, removed, and changed. There is a data type that is similar to lists but that can’t be changed, and that is called a tuple.

Tuples

A tuple is used for grouping data. It is an immutable, or unchangeable, ordered sequence of elements.

Tuples are very similar to lists, but they use parentheses ( ) instead of square brackets and because they are immutable their values cannot be modified.

A tuple looks like this:

('blue coral', 'staghorn coral', 'pillar coral')

We can store a tuple in a variable and print it out:

coral = ('blue coral', 'staghorn coral', 'pillar coral')
print(coral)

('blue coral', 'staghorn coral', 'pillar coral')

Like in the other data types, Python prints out the tuple just as we had typed it, with parentheses containing a sequence of values.

Dictionaries

The dictionary is Python’s built-in mapping type. This means that dictionaries map keys to values and these key-value pairs are a useful way to store data in Python. A dictionary is constructed with curly braces on either side { }.

Typically used to hold data that are related, such as the information contained in an ID, a dictionary looks like this:

{'name': 'Sammy', 'animal': 'shark', 'color': 'blue', 'location': 'ocean'}

You will notice that in addition to the curly braces, there are also colons throughout the dictionary. The words to the left of the colons are the keys. Keys can be made up of any immutable data type. The keys in the dictionary above are: 'name', 'animal', 'color', 'location'.

The words to the right of the colons are the values. Values can be comprised of any data type. The values in the dictionary above are: 'Sammy', 'shark', 'blue', 'ocean'.

Like the other data types, let’s store the dictionary inside a variable, and print it out:

sammy = {'name': 'Sammy', 'animal': 'shark', 'color': 'blue',  'location': 'ocean'}
print(sammy)

{'color': 'blue', 'animal': 'shark', 'name': 'Sammy', 'location': 'ocean'}

If we want to isolate Sammy’s color, we can do so by calling sammy['color']. Let’s print that out:

print(sammy['color'])

blue

As dictionaries offer key-value pairs for storing data, they can be important elements in your Python program.

Conclusion

At this point, you should have a better understanding of some of the major data types that are available for you to use in Python. Each of these data types will become important as you develop programming projects in the Python language.

You can learn about each of the data types above in more detail by reading the following specific tutorials: - Numbers - Booleans - Strings - Lists - Tuples - Dictionaries

Once you have a solid grasp of data types available to you in Python, you can learn how to convert data types.