This tutorial on 'Variables and Data Types in Python' will help you establish a foothold on Python by helping you learn basic concepts like variables and data types.
In this Python tutorial, we will learn about Python variables and data types being used in Python.
We will also learn about converting one data type to another in Python and local and global variables in Python.
So, let’s begin with Python variables and data types Tutorial.
What are Python Variables?
A variable is a container for a value. It can be assigned a name, you can use it to refer to it later in the program.
Based on the value assigned, the interpreter decides its data type. You can always store a different type in a variable.
For example, if you store 7 in a variable, later, you can store ‘Dinosaur’.
There are certain rules to what you can name a variable(called an identifier).
>>> 9lives=9
Output
SyntaxError: invalid syntax
>>> flag=0
>>> flag
>>> _9lives='cat'
>>> _9lives
Output
‘cat’
The rest of the identifier may contain letters(A-Z/a-z), underscores(_), and numbers(0-9).
>>> year2='Sophomore'
>>> year2
Output
‘Sophomore’
>>> _$$=7
Output
SyntaxError: invalid syntax
>>> name='Ayushi'
>>> name
Output
‘Ayushi’
>>> Name
Output
Traceback (most recent call last):
File “<pyshell#21>”, line 1, in <module>
Name
NameError: name ‘Name’ is not defined
and | def | False | import | not | True |
as | del | finally | in | or | try |
assert | elif | for | is | pass | while |
break | else | from | lambda | with | |
class | except | global | None | raise | yield |
continue | exec | if | nonlocal | return |
To assign a value to Python variables, you don’t need to declare its type.
You name it according to the rules stated in section 2a, and type the value after the equal sign(=).
>>> age=7
>>> print(age)
Output
7
>>> age='Dinosaur'
>>> print(age)
Output
Dinosaur
However, age=Dinosaur doesn’t make sense. Also, you cannot use Python variables before assigning it a value.
>>> name
Output
Traceback (most recent call last):
File “<pyshell#8>”, line 1, in <module>
name
NameError: name ‘name’ is not defined
You can’t put the identifier on the right-hand side of the equal sign, though. The following code causes an error.
>>> 7=age
Output
SyntaxError: can’t assign to literal
Neither can you assign Python variables to a keyword.
>>> False=choice
Output
SyntaxError: can’t assign to keyword
You can assign values to multiple Python variables in one statement.
>>> age,city=21,'Indore'
>>> print(age,city)
Output
21 Indore
Or you can assign the same value to multiple Python variables.
>>> age=fav=7
>>> print(age,fav)
Output
7 7
This is how you assign values to Python Variables
Swapping means interchanging values. To swap Python variables, you don’t need to do much.
>>> a,b='red','blue'
>>> a,b=b,a
>>> print(a,b)
Output
blue red
You can also delete Python variables using the keyword ‘del’.
>>> a='red'
>>> del a
>>> a
Output
Traceback (most recent call last):
File “<pyshell#39>”, line 1, in <module>
a
NameError: name ‘a’ is not defined
Although we don’t have to declare a type for Python variables, a value does have a type. This information is vital to the interpreter.
Python supports the following data types.
There are four numeric Python data types.
int stands for integer. This Python Data Type holds signed integers. We can use the type() function to find which class it belongs to.
>>> a=-7
>>> type(a)
Output
<class ‘int’>
An integer can be of any length, with the only limitation being the available memory.
>>> a=9999999999999999999999999999999
>>> type(a)
Output
<class ‘int’>
This Python Data Type holds floating-point real values. An int can only store the number 3, but float can store 3.25 if you want.
>>> a=3.0
>>> type(a)
Output
<class ‘float’>
This Python Data type holds a long integer of unlimited length. But this construct does not exist in Python 3.x.
This Python Data type holds a complex number. A complex number looks like this: a+bj Here, a and b are the real parts of the number, and j is imaginary.
>>> a=2+3j
>>> type(a)
Output
<class ‘complex’>
Use the isinstance() function to tell if Python variables belong to a particular class. It takes two parameters- the variable/value, and the class.
>>> print(isinstance(a,complex))
Output
True
A string is a sequence of characters. Python does not have a char data type, unlike C++ or Java. You can delimit a string using single quotes or double-quotes.
>>> city='Ahmedabad'
>>> city
Output
‘Ahmedabad’
>>> city="Ahmedabad"
>>> city
Output
‘Ahmedabad’
To span a string across multiple lines, you can use triple quotes.
>>> var="""If
only"""
>>> var
Output
‘If\n\tonly’
>>> print(var)
Output
If
Only
>>> """If
only"""
Output
‘If\n\tonly’
As you can see, the quotes preserved the formatting (\n is the escape sequence for newline, \t is for tab).
You can display a character from a string using its index in the string. Remember, indexing starts with 0.
>>> lesson='disappointment'
>>> lesson[0]
Output
‘d’
You can also display a burst of characters in a string using the slicing operator [].
>>> lesson[5:10]
Output
‘point’
This prints the characters from 5 to 9.
String formatters allow us to print characters and values at once. You can use the % operator.
>>> x=10;
>>> printer="Dell"
>>> print("I just printed %s pages to the printer %s" % (x, printer))
Or you can use the format method.
>>> print("I just printed {0} pages to the printer {1}".format(x, printer))
>>> print("I just printed {x} pages to the printer {printer}".format(x=7, printer="Dell"))
A third option is to use f-strings.
>>> print(f"I just printed {x} pages to the printer {printer}")
You can concatenate(join) strings.
>>> a='10'
>>> print(a+a)
Output
1010
However, you cannot concatenate values of different types.
>>> print('10'+10)
Output
Traceback (most recent call last):File “<pyshell#89>”, line 1, in <module>;
print(’10’+10)
TypeError: must be str, not int
A list is a collection of values. Remember, it may contain different types of values.
To define a list, you must put values separated with commas in square brackets. You don’t need to declare a type for a list either.
>>> days=['Monday','Tuesday',3,4,5,6,7]
>>> days
Output
[‘Monday’, ‘Tuesday’, 3, 4, 5, 6, 7]
You can slice a list the way you’d slice a string- with the slicing operator.
>>> days[1:3]
Output
[‘Tuesday’, 3]
Indexing for a list begins with 0, like for a string. A Python doesn’t have arrays.
Python supports an inbuilt function to calculate the length of a list.
>>> len(days)
Output
7
A list is mutable. This means that you can reassign elements later on.
>>> days[2]='Wednesday'
>>> days
Output
[‘Monday’, ‘Tuesday’, ‘Wednesday’, 4, 5, 6, 7]
To iterate over the list we can use the for loop. By iterating, we can access each element one by one which is very helpful when we need to perform some operations on each element of list.
nums = [1,2,5,6,8]
for n in nums:
print(n)
Output
1
2
5
6
8
A list may have more than one dimension.
>>> a=[[1,2,3],[4,5,6]]
>>> a
Output
[[1, 2, 3], [4, 5, 6]]
A tuple is like a list. You declare it using parentheses instead.
>>> subjects=('Physics','Chemistry','Maths')
>>> subjects
Output
(‘Physics’, ‘Chemistry’, ‘Maths’)
You access a tuple the same way as you’d access a list. The same goes for slicing it.
>>> subjects[1]
Output
‘Chemistry’
>>> subjects[0:2]
Output
(‘Physics’, ‘Chemistry’)
Python tuple is immutable. Once declared, you can’t change its size or elements.
>>> subjects[2]='Biology'
Output
Traceback (most recent call last):
File “<pyshell#107>”, line 1, in <module>
subjects[2]=’Biology’
TypeError: ‘tuple’ object does not support item assignment
>>> subjects[3]='Computer Science'
Output
Traceback (most recent call last):
File “<pyshell#108>”, line 1, in <module>
subjects[3]=’Computer Science’
TypeError: ‘tuple’ object does not support item assignment
A dictionary holds key-value pairs. Declare it in curly braces, with pairs separated by commas. Separate keys and values by a colon(:).
>>> person={'city':'Ahmedabad','age':7}
>>> person
Output
{‘city’: ‘Ahmedabad’, ‘age’: 7}
The type() function works with dictionaries too.
>>> type(person)
Output
<class ‘dict’>
To access a value, you mention the key in square brackets.
>>> person['city']
Output
‘Ahmedabad’
You can reassign a value to a key.
>>> person['age']=21
>>> person['age']
Output
21
Use the keys() function to get a list of keys in the dictionary.
>>> person.keys()
Output
dict_keys([‘city’, ‘age’])
A Boolean value can be True or False.
>>> a=2>1
>>> type(a)
Output
<class ‘bool’>
A set can have a list of values. Define it using curly braces.
>>> a={1,2,3}
>>> a
Output
{1, 2, 3}
However, a set is unordered, so it doesn’t support indexing.
>>> a[2]
Output
Traceback (most recent call last):
File “<pyshell#127>”, line 1, in <module>
a[2]
TypeError: ‘set’ object does not support indexing
Also, it is mutable. You can change its elements or add more. Use the add() and remove() methods to do so.
>>> a={1,2,3,4}
>>> a
Output
{1, 2, 3, 4}
>>> a.remove(4)
>>> a
Output
{1, 2, 3}
>>> a.add(4)
>>> a
Output
{1, 2, 3, 4}
Since Python is dynamically-typed, you may want to convert a value into another type. Python supports a list of functions for the same.
It converts the value into an int.
>>> int(3.7)
Output
3
Notice how it truncated 0.7 instead of rounding the number off to 4. You can also turn a Boolean into an int.
>>> int(True)
However, you cannot turn a string into an int. It throws an error.
>>> int("a")
Output
Traceback (most recent call last):
File “<pyshell#135>”, line 1, in <module>;
int(“a”)
ValueError: invalid literal for int() with base 10: ‘a’
However, if the string has only numbers, then you can.
>>> int("77")
Output
77
It converts the value into a float.
>>> float(7)
Output
7.0
>>> float(7.7)
Output
7.7
>>> float(True)
Output
1.0
>>> float("11")
Output
11.0
You can also use ‘e’ to denote an exponential number.
>>> float("2.1e-2")
Output
0.021
>>> float(2.1e-2)
Output
0.021
However, this number works even without the float() function.
>>> 2.1e-2
Output
0.021
It converts the value into a string.
>>> str(2.1)
Output
‘2.1’
>>> str(7)
Output
‘7’
>>> str(True)
Output
‘True’
You can also convert a list, a tuple, a set, or a dictionary into a string.
>>> str([1,2,3])
Output
‘[1, 2, 3]’
It converts the value into a boolean.
>>> bool(3)
Output
True
>>> bool(0)
Output
False
>>> bool(True)
Output
True
>>> bool(0.1)
Output
True
You can convert a list into a Boolean.
>>> bool([1,2])
Output
True
The function returns False for empty constructs.
>>> bool()
Output
False
>>> bool([])
Output
False
>>> bool({})
Output
False
None is a keyword in Python that represents an absence of value.
>>> bool(None)
Output
False
It converts the value into a set.
>>> set([1,2,2,3])
Output
{1, 2, 3}
>>> set({1,2,2,3})
Output
{1, 2, 3}
It converts the value into a list.
>>> del list
>>> list("123")
Output
[‘1’, ‘2’, ‘3’]
>>> list({1,2,2,3})
Output
[1, 2, 3]
>>> list({"a":1,"b":2})
Output
[‘a’, ‘b’]
However, the following raises an error.
>>> list({a:1,b:2})
Output
Traceback (most recent call last):
File “<pyshell#173>”, line 1, in <module>;
list({a:1,b:2})
TypeError: unhashable type: ‘set’
It converts the value into a tuple.
>>> tuple({1,2,2,3})
Output
(1, 2, 3)
You can try your own combinations. Also try composite functions.
>>> tuple(list(set([1,2])))
Output
(1, 2)
Another classification of Python variables is based on scope.
When you declare a variable in a function, class, or so, it is only visible in that scope. If you call it outside of that scope, you get an ‘undefined’ error.
>>> def func1():
uvw=2
print(uvw)
>>> func1()
Output
2
>>> uvw
Output
Traceback (most recent call last):
File “<pyshell#76>”, line 1, in <module>
uvw
NameError: name ‘uvw’ is not defined[/php]
Here, the variable uvw is local to function func1().
When you declare a variable outside any context/scope, it is visible in the whole program.
>>> xyz=3
>>> def func2():
xyz=0
xyz+=1
print(xyz)
>>> func2()
Output
1
>>> xyz
Output
3
You can use the ‘global’ keyword when you want to treat a variable as global in a local scope.
>>> foo=1
>>> def func2():
global foo
foo=3
print(foo)
>>> func2()
Output
3
>>> foo
Output
3
In this tutorial on Python Variables and data types, we learned about different Python variables and data types with examples.
We looked at the naming rules, and defining and deleting them. Then we saw different types of data- numbers, strings, lists, dictionaries, tuples, sets, and many more.
We also learned how to convert one variable type into another and local and global variables in Python.
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