Python Data Types

Table of Contents

• Data Types
• Integers and Floating-point Numbers
• Strings
  • String Methods
  • Mixing Strings and Variables
  • Indexing and Slicing Strings
    • Indexing Strings
    • Slicing Strings
• Booleans
  • Comparison Operators
  • Logical Operators

Data Types

Variables can store data of different types, and different data types serve different purposes. Python has the following data types built-in by default, in these categories:

In this section, we will discuss the most important basic data types:

• int
• float
• str
• bool

In the next section, we shall discuss the more advanced data structures: list, tuple, range, dict and set.

Integers and Floating-point Numbers

The data types int and float represent integers and floating-point numbers, respectively. We can understand floating-point numbers simply as decimals. To find out the data type of a given object, use the type() function.

Example

1type(5)

int

The above shows that the type of the number 5 is int.

Example

1type(6.1)

float

This means that the type of the number 6.1 is float.

If you want to force a number to be a float instead of an int, use either a trailing decimal point or the float() constructor:

Example

1type(5.)  # trailing decimal

float

Example

1type(float(5))  # float constructor

float

Conversely, Using the int() constructor, you can turn a float into an int. If the fractional part is not zero, it will be truncated.

Example

1int(6.8)  # turn a float into an int (truncated)

6

1type(int(6.8))  # type

int

Strings

We can understand strings simply as texts. In Python, strings can be expressed by using either double quotes (") or single quotes (’). The only condition is that you have to start and end the string with the same type of quotes.

Example

1str1 = "I am a string in double quotes."
2print(str1)
3type(str1)

I am a string in double quotes.

str

Example

1str2 = 'I am a string in single quotes.'
2print(str2)
3type(str2)

I am a string in single quotes.

str

You can use operator + to concatenate strings or * to repeat strings.

Example

1"This is a course on " + 'Python.'  # concatenation

'This is a course on Python.'

Example

1'This sentence is repeated 3 times. '*3  # repetition

'This sentence is repeated 3 times. This sentence is repeated 3 times. This sentence is repeated 3 times. '

ADVERTISEMENT

String Methods

The title() method changes each word to title case so that each word begins with a capital letter.

Example

1name = "tom cruise"
2name.title()

'Tom Cruise'

Several other useful methods are available for dealing with case as well. For example, you can change a string to all uppercase or all lowercase letters using the upper() and lower() methods, respectively.

Example

1name = "Donald Trump"
2name.upper()

'DONALD TRUMP'

Example

1name.lower()

'donald trump'

Note that all string methods do not change the original string but instead return a new string with the changed attributes. In the above example, the original variable (name) remains unchanged.

1name

'Donald Trump'

To keep the changes, you can either assign the original variable to the new value or assign a new variable to the new value.

Example

1name = "Donald Trump"
2name = name.upper()  # original variable name assigned to new object
3name

'DONALD TRUMP'

Example

1name = "Donald Trump"
2name1 = name.upper()  # new variable name assigned to new object
3name1

'DONALD TRUMP'

We can count the number of occurrences of a certain letter in a string using the count() method.

Example

1word = "testimonial"
2word.count('t')   # count number of occurrences of 't'

2

Example

1sentence = "Hello I am back!"
2sentence.count(" ") # count the number of blank spaces.

3

We can use the replace() method to make replacements in a string.

Example

1sentence.replace('back','here') # 'back' is replaced with 'here'

'Hello I am here!'

We can also split a sentence into a list of words.

Example

1sentence.split() # split by white space

['Hello', 'I', 'am', 'back!']

The above output is called a Python list which we will discuss in a later section.

Example

1sentence.split("a") # split by a letter

['Hello I ', 'm b', 'ck!']

We can also check if the string starts with certain character(s).

Example

1sentence.startswith("H")

True

Example

1sentence.startswith("Hel")

True

Example

1sentence.startswith("el")

False

Finally, we can employ the center() method to center a string to any specified length. For example, the following code returns a string with 50 characters, with the input string centered and missing space on each side filled with a specified character “=”.

Example

1
2txt = "DigitalBlackboard"
3
4txt.center(50, "=") # returns a string with 50 characters with tex centered and

================DigitalBlackboard=================

The following table summarizes some of the most useful string methods.

ADVERTISEMENT

Mixing Strings and Variables

If we want to mix strings with variables, we can employ f-strings, or formatted string literals. Simply put an f in front of your string and variables in between curly braces:

Example

1year = 2016
2event = 'Election'
3f'Results of the {year} {event}'

'Results of the 2016 Election'

Example

1bags = 3
2oranges_per_bag = 4
3f'We have a total of {bags*oranges_per_bag} oranges.'

'We have a total of 12 oranges.'

Example

1import math
2apples = 20
3bags = 6
4f'If we distribute {apples} apples to {bags} bags, we are left with {int(math.remainder(apples,bags))} apples.'

'If we distribute 20 apples to 6 bags, we are left with 2 apples.'

We can also have multiline f-Strings. But remember that you need to place an f in front of each line of a multiline string.

Example

1name = "Julia"
2age = "28"
3country = "Singapore"
4message = (
5    f"Her name is {name}. "
6    f"Her age is {age} and "
7    f"she lives in {country}."
8)
9message

'Her name is Julia. Her age is 28 and she lives in Singapore.'

Indexing and Slicing Strings

We can check the size of the string by using the built-in function len().

Example

1s="This is London"
2len(s) #including spaces

14

To access to specific elements of a string (which is a sequence of characters), we make use of indexing and slicing.

Indexing Strings

Python is zero index-based, which means that the first element in a sequence has an index of 0. Negative indices from -1 allow us to refer to elements from the end of the sequence.

Example

1country = "Singapore"
2country[0] # first element

'S'

Example

1country[1] #second element

'i'

Example

1country[-1] # first element from the end

'e'

Example

1country[-3] # third element from the end

'o'

Slicing Strings

If you want to get more than one element from a sequence, you can use the slicing syntax, which works as follows:

sequence[start:stop:step]

Python uses half-open intervals: the start index is included while the stop index is not.

Let’s create a table of indices of the string “Singapore”.

Example

1print(country)
2country[:2] # first 2 elements

Singapore

'Si'

Example

1country[1:4] # all elements from index 1 to 3

'ing'

Example

1country[2:] # all elements starting with index 2

'ngapore'

Example

1country[-4:-1] # all elements from index -4 to -2

'por'

Example

1country[::2] # every second element

'Snaoe'

Example

1country[::-1] # spelt backwards

'eropagniS'

Example

1country[-2:-5:-1] # all elements from index -2 to index -4 backwards

'rop'

Python also allows us to chain multiple index and slice operations together.

Example

Step 1:

Step 2:

1country[:5][2:]

'nga'

Example

1f'The 2-letter code of {country.title()} is {country.upper()[0] + country.upper()[3]}.'

'The 2-letter code of Singapore is SG.'

ADVERTISEMENT

Booleans

Boolean is another basic data type in Python. The Boolean values in Python are True or False.

The majority of objects in python are True, but there are some that evaluate to False including None, False, 0 or empty data types (e.g. empty strings).

Example

1type(True) # True is a Boolean type.

bool

Example

1type(False) # False is a Boolean type.

bool

Example

1bool(1)

True

Example

1bool(0)

False

Example

1bool(False)

False

Example

1bool(None) # None is a built-in constant and represents the absence of a value.

False

Example

1bool("") # empty string

False

Example

1bool("Hello World!")

True

Comparison Operators

Boolean expressions are expressions that yield Boolean values (i.e. True or False) using operators called Boolean operators. Boolean operators can be divided into

• comparison operators
• logical operators

We dicuss comparison operators in this section and logical operators in the next.

Comparison operators are used to compare values and evaluate the Boolean expression down to a single Boolean value (either True or False).

Example

11==2 # 1 equal to 2

False

Example

12>1 # 2 greater than 1

True

Example

13!=4 # 3 not equal to 4

True

In the above examples, the comparison operators are ==, > and !=. The following table displays the complete list of Boolean comparison operators.

Note that Booleans are considered a numeric type in Python. True has a value of 1 and False has a value of 0.

Example

1True == 1

True

Example

1False == 0

True

Example

1True+True

2

Logical Operators

The logical operators in Python are: and, or and not. We can further divide them into

• binary operators
• unary operators

The operators and and or require 2 operands and are thus called binary operators. On the other hand, not is a unary operator which works on one operand.

Example

1x=True
2y=False
3x and y # binary

False

Example

1x or y # binary

True

Example

1not x # unary

False

Example

13>2 and 4<5

True