Python data type
last modified January 29, 2024
In this article we cover Python data types.
Computer programs, such as spreadsheets, text editors, calculators, or chat clients, work with data. Tools to work with various data types are essential part of a modern computer language.
Python data type definition
Data type is a set of values and the allowable operations on those values.
Python has a great set of useful data types. Python's data types are built in the core of the language. They are easy to use and straightforward.
Python boolean
In Python programming language, the Boolean datatype is a primitive datatype
having one of two values: True or False. This is a
fundamental data type.
Happy parents are waiting a child to be born. They have chosen a name for both possibilities. If it is going to be a boy, they might have chosen John. If it is going to be a girl, they might have chosen Victoria.
#!/usr/bin/python
# kid.py
import random
male = False
male = bool(random.randint(0, 1))
if male:
print("We will use name John")
else:
print("We will use name Victoria")
The script uses a random integer generator to simulate our case.
import random
Here we import the random module that is used to calculate random numbers.
male = bool(random.randint(0, 1))
Here we use two functions. the randint function returns a random
number from the given integer boundaries. In our case 0 or 1. The
bool function converts the integers to boolean values.
if male:
print("We will use name John")
else:
print("We will use name Victoria")
We print the name. The if keyword works with boolean values. If the
male is True, we print the "We will use name John" to
the console. If it has a False value, we print the other string.
The following script shows some common values that are considered to be
True or False.
#!/usr/bin/python
# bool_fun.py
print(bool(True))
print(bool(False))
print(bool("text"))
print(bool(""))
print(bool(' '))
print(bool(0))
print(bool())
print(bool(3))
print(bool(None))
The example prints nine boolean values.
$ ./bool_fun.py True False True False True False False True False
Python None
There is another special data type — None. This data type means
non existent, not known, or empty.
#!/usr/bin/python
# none.py
def function():
pass
print(function())
In our example, we define a function. Functions will be covered later in the
tutorial. The function does nothing. It does not explicitly return any value.
Such a function will implicitly return None.
$ ./none.py None
Python numbers
In Python programming language, we have integer numbers, floating point numbers, and complex numbers.
If we work with integers, we deal with discrete entities. We would use integers to count apples.
#!/usr/bin/python
# apples.py
# number of baskets
baskets = 16
# number of apples in a basket
apples_in_basket = 24
# we get the total number of apples
total = baskets * apples_in_basket
print("There are total of", total, "apples")
In our script, we count the total amount of apples. We use the multiplication operation.
$ ./apples.py There are total of 384 apples
Floating point numbers represent real numbers in computing. Real numbers measure continuous quantities. Let's say a sprinter for 100m ran 9.87s. What is his speed in km/h?
#!/usr/bin/python
# sprinter.py
# 100 m is 0.1 km
distance = 0.1
# 9.87 s is 9.87/60*60 h
time = 9.87 / 3600
speed = distance / time
print("The average speed of a sprinter is {0} km/h".format(speed))
To get the speed, we divide the distance by the time.
print("The average speed of a sprinter is {0} km/h".format(speed))
We build the message with the format function and print
it to the console.
$ ./sprinter.py The average speed of a sprinter is 36.4741641337 km/h
This is the output of the sprinter.py script.
Value 36.4741641337 is a floating point number.
Python string
String is a data type representing textual data in computer programs.
Strings in Python can be created using single quotes, double quotes, and triple quotes. When we use triple quotes, strings can span several lines without using the escape character.
#!/usr/bin/python # strings.py a = "proximity alert" b = 'evacuation' c = """ requiem for a tower """ print(a) print(b) print(c)
In our example we assign three string literals to a,
b, and c variables. Then we print them to the console.
$ ./strings.py proximity alert evacuation requiem for a tower
When we work with strings, we can use escape sequences. Escape sequences are special characters that have a specific purpose when used within a string.
print(" bbb\raaa") # prints aaabbb
The carriage return \r is a control character for end of
line return to beginning of line.
#!/usr/bin/python
# strophe.py
print("Incompatible, it don't matter though\n'cos someone's bound to hear my cry")
print("Speak out if you do\nYou're not easy to find")
The new line is a control character which begins a new line of text.
$ ./strophe.py Incompatible, it don't matter though 'cos someone's bound to hear my cry Speak out if you do You're not easy to find
Next we examine the backspace control character.
print("Python\b\b\booo") # prints Pytooo
The backspace control character \b moves the cursor one character
back. In our case, we use three backspace characters to delete three letters and
replace them with three o characters.
print("Towering\tinferno") # prints Towering inferno
The horizontal tab puts a space between text.
"Johnie's dog" 'Johnie\'s dog'
Single and double quotes can be nested. Or in case we use only single quotes, we can use the backslash to escape the default meaning of a single quote.
print("eagle has", len("eagle"), "characters")
We can use the len function to calculate the length
of the string in characters.
If we append an r to the string, we get a raw string. The
escape sequences are not interpreted.
#!/usr/bin/python # raw.py print(r"Another world\n")
$ ./raw.py Another world\n
We get the string with the new line character included.
In the next example, we show string multiplication and concatenation.
#!/usr/bin/python
# strings2.py
print("eagle " * 5)
print("eagle " "falcon")
print("eagle " + "and " + "falcon")
The * operator repeats the string n times. In our case five times.
Two string literals next to each other are automatically concatenated. We can
also use the + operator to explicitly concatenate strings.
$ ./strings2.py eagle eagle eagle eagle eagle eagle falcon eagle and falcon
Python has several built-in data types for working with collections of values: tuples, lists, sets, and dictionaries.
Python tuple
A tuple is an immutable sequence data type. The tuple can contain mixed data types.
fruits = ("oranges", "apples", "bananas")
Tuples are created using round brackets. Here we have a tuple consisting of three fruit types.
fruits = "apples", "oranges", "bananas"
print(fruits) # prints ('apples', 'oranges', 'bananas')
The parentheses are not mandatory. We can omit them.
#!/usr/bin/python
# tuples.py
first = (1, 2, 3)
second = (4, 5, 6)
print("len(first) : ", len(first))
print("max(first) : ", max(first))
print("min(first) : ", min(first))
print("first + second :", first + second)
print("first * 3 : ", first * 3)
print("1 in first : ", 1 in first)
print("5 not in second : ", 5 not in second)
This example shows several basic operations with tuples. The len
function returns the number of elements in the first tuple. The max
function returns the maximum value and the min the minimum value.
The addition operator adds two tuples, the multiplication operator multiplies
the tuple. The in operator determines if the value is in the tuple.
$ ./tuples.py len(first) : 3 max(first) : 3 min(first) : 1 first + second : (1, 2, 3, 4, 5, 6) first * 3 : (1, 2, 3, 1, 2, 3, 1, 2, 3) 1 in first : True 5 not in second : False
Next we do some indexing.
#!/usr/bin/python
# tuples2.py
five = (1, 2, 3, 4, 5)
print("five[0] : ", five[0])
print("five[-1] : ", five[-1])
print("five[-2] : ", five[-2])
print("five[:] : ", five[:])
print("five[0:4] : ", five[0:4])
print("five[1:2] : ", five[1:2])
print("five[:2] : ", five[:2])
print("five[:-1] : ", five[:-1])
print("five[:9] : ", five[:9])
To get a value from a tuple, we use square brackets []. Note that
we count indexes from 0. If there are five objects in a tuple, the indexes are
0...4. If we use a negative index, we get a value from the end of the tuple. So
index -1 gets the last element, -2 gets the last but one element.
Python enables to create slices from tuples. For this we use the
: delimiter. For instance, [0:4] gives (1, 2, 3,
4). Note that the last element is not included.
We can omit one or both indexes in a slice. The [:4] gives
(1, 2, 3, 4). It goes from the first element. The [0:]
gives (1, 2, 3, 4, 5). This time, the last element is included. If we go out of
bounds, we simply get all elements in the tuple.
$ ./tuples2.py five[0] : 1 five[-1] : 5 five[-2] : 4 five[:] : (1, 2, 3, 4, 5) five[0:4] : (1, 2, 3, 4) five[1:2] : (2,) five[:2] : (1, 2) five[:-1] : (1, 2, 3, 4) five[:9] : (1, 2, 3, 4, 5)
Tuples can contain several mix data types.
#!/usr/bin/python
# tuples_mix.py
mix = (1, 2, "solaris", (1, 2, 3))
print("mix[1] :", mix[1])
print("mix[2] :", mix[2])
print("mix[3] :", mix[3])
print("mix[3][0] :", mix[3][0])
print("mix[3][1] :", mix[3][1])
print("mix[3][2] :", mix[3][2])
In our example, we have put numbers, a string, and a tuple into the mix tuple.
$ ./tuples_mix.py mix[1] : 2 mix[2] : solaris mix[3] : (1, 2, 3) mix[3][0] : 1 mix[3][1] : 2 mix[3][2] : 3
To get the elements from the nested tuple, we use two square brackets.
We have an exception when we work with tuples containing one element. Parentheses are also used in expressions. How do we distinguish between an expression and a one element tuple? The creators of the Python programming language decided to use a comma to denote that we are using a tuple.
#!/usr/bin/python # tuple_one.py print((3 + 7)) print((3 + 7, ))
In the first case we have and expression. We print number 10 to the console. In the second case we deal with a tuple. We print a tuple containing number 10.
$ ./tuple_one.py 10 (10,)
Python list
A list is a mutable sequence data type. It can contain mixed data types. A list and a tuple share many common features. Because a list is a modifiable data type, it has some additional operations. A whole chapter is dedicated to the Python list.
actors = ["Jack Nicholson", "Antony Hopkins", "Adrien Brody"]
The list is created using the square brackests [].
#!/usr/bin/python # simple_list.py num = [0, 2, 5, 4, 6, 7] print(num[0]) print(num[2:]) print(len(num)) print(num + [8, 9])
As we have stated previously, we can use the same operations on lists as on tuples.
$ ./list_simple.py 0 [5, 4, 6, 7] 6 [0, 2, 5, 4, 6, 7, 8, 9]
Next we sort a list.
#!/usr/bin/python # list_sorting.py numbers = [4, 3, 6, 1, 2, 0, 5] print(numbers) numbers.sort() print(numbers)
In our script we have a list of numbers. To sort those numbers, we
use the built-in sort function.
$ ./list_sorting.py [4, 3, 6, 1, 2, 0, 5] [0, 1, 2, 3, 4, 5, 6]
The reverse function will sort the elements of a list in reverse
order.
numbers.reverse() # [5, 4, 3, 2, 1, 0]
Counting elements in a list is done with the count method.
#!/usr/bin/python
# list_counting_elements.py
numbers = [0, 0, 2, 3, 3, 3, 3]
print("zero is here", numbers.count(0), "times")
print("one is here", numbers.count(1), "times")
print("two is here", numbers.count(2), "time")
print("three is here", numbers.count(3), "times")
The script counts number occurrences in a list.
$ ./list_counting_elements.py zero is here 2 times one is here 0 times two is here 1 time three is here 4 times
Next, we deal with inserting and deleting items from the list.
#!/usr/bin/python
# list_modify.py
names = []
names.append("Frank")
names.append("Alexis")
names.append("Erika")
names.append("Ludmila")
print(names)
names.insert(0, "Adriana")
print(names)
names.remove("Frank")
names.remove("Alexis")
del names[1]
print(names)
del names[0]
print(names)
In our example we first create an empty names list. We use the
append function to append new items to the list. The elements are
appended in the consecutive way. The insert function inserts new
elements at a given position. The existing elements are not deleted, they are
relocated. The remove function removes a specific item from the
list. If we want to delete an item based on the index, we use the
del keyword.
$ ./list_modify.py ['Frank', 'Alexis', 'Erika', 'Ludmila'] ['Adriana', 'Frank', 'Alexis', 'Erika', 'Ludmila'] ['Adriana', 'Ludmila'] ['Ludmila']
There following program presents additional two functions.
#!/usr/bin/python # list_modify2.py first = [1, 2, 3] second = [4, 5, 6] first.extend(second) print(first) first[0] = 11 first[1] = 22 first[2] = 33 print(first) print(first.pop(5)) print(first)
The extend method appends a whole list to another list. To modify
an element in a list, we can use the assignment operator. The pop
method takes an item from the list and returns it.
$ ./list_modify2.py [1, 2, 3, 4, 5, 6] [11, 22, 33, 4, 5, 6] 6 [11, 22, 33, 4, 5]
In the following example, we find out indexes of elements.
#!/usr/bin/python # list_index.py numbers = [0, 1, 2, 3, 3, 4, 5] print(numbers.index(1)) print(numbers.index(3))
To find an index in a list, we use the index method. If there are
more occurrences of an element, the method returns the index of the first
element.
$ ./list_index.py 1 3
Next we do some transformations.
#!/usr/bin/python # list_transform.py first = [1, 2, 3] second = (4, 5, 6) print(tuple(first)) print(list(second)) print(first) print(second)
We can use tuple function to create a tuple from a list and
list function to create a list from a tuple. Note that the original
objects are not modified; the functions only return those transformed
collections.
$ ./list_transform.py (1, 2, 3) [4, 5, 6] [1, 2, 3] (4, 5, 6)
Python set
A set is an unordered collection of data with no duplicate
elements. A set supports operations like union, intersection, or difference;
similar as in Mathematics.
#!/usr/bin/python
set1 = set(['a', 'b', 'c', 'c', 'd'])
set2 = set(['a', 'b', 'x', 'y', 'z'])
print("set1: " , set1)
print("set2: " , set2)
print("intersection: ", set1 & set2)
print("union: ", set1 | set2)
print("difference: ", set1 - set2)
print("symmetric difference: ", set1 ^ set2)
In our example we have two sets. We use the set function to create
sets. The intersection operation returns elements that are both in
set1 and set2. The union operation returns all
elements from both sets. The difference returns elements that are in the
set1 but not is set2. And finally, the symmetric
difference returns elements that are in set1 or set2,
but not in both.
$ ./sets.py set1: set(['a', 'c', 'b', 'd']) set2: set(['a', 'x', 'b', 'y', 'z']) intersection: set(['a', 'b']) union: set(['a', 'c', 'b', 'd', 'y', 'x', 'z']) difference: set(['c', 'd']) symmetric difference: set(['c', 'd', 'y', 'x', 'z'])
Next we introduce some other operations with sets.
#!/usr/bin/python
# sets2.py
set1 = set([1, 2])
set1.add(3)
set1.add(4)
set2 = set([1, 2, 3, 4, 6, 7, 8])
set2.remove(8)
print(set1)
print(set2)
print("Is set1 subset of set2 ? :", set1.issubset(set2))
print("Is set1 superset of set2 ? :", set1.issuperset(set2))
set1.clear()
print(set1)
The add method adds an item to the set. The remove
item removes an item from a set. The clear method removes all items
from the set. The set1 is superset of set2 if every
element in set2 is also in set1. The set1
is a subset of set2 if every element in set1 is also
in set2.
$ ./sets2.py set([1, 2, 3, 4]) set([1, 2, 3, 4, 6, 7]) Is set1 subset of set2 ? : True Is set1 superset of set2 ? : False set([])
If we need an immutable set, we can create a frozen set with the
frozenset function.
fs = frozenset(['a', 'b', 'c'])
This line creates a frozen set from a list.
Python dictionary
A Python dictionary is a group of key-value pairs. The elements in a dictionary are indexed by keys. Keys in a dictionary are required to be unique. Because of the importance of the dictionary data type, a whole chapter covers the dictionary in this Python tutorial.
#!/usr/bin/python
# dictionary_simple.py
words = { 'girl': 'Maedchen', 'house': 'Haus', 'death': 'Tod' }
print(words['house'])
print(words.keys())
print(words.values())
print(words.items())
print(words.pop('girl'))
print(words)
words.clear()
print(words)
Our first example shows some basic usage of the dictionary data type. We print a
specific value, keys and values of the dictionary. The items method
returns a list of dictionarie's (key, value) pairs as tuples.
$ ./dictionary_simple.py
Haus
['house', 'girl', 'death']
['Haus', 'Maedchen', 'Tod']
[('house', 'Haus'), ('girl', 'Maedchen'), ('death', 'Tod')]
Maedchen
{'house': 'Haus', 'death': 'Tod'}
{}
Source
Python data types - documentation
In this article we have described Python data types.
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