Python Variables and Data Types – A complete guide for beginners

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?

Python lets you store information in variables. Think of a variable as a named box where you keep data while your program runs. You choose a short, clear name, then use the equal sign (=) to place a value inside that box.

For example, if you store 7 in a variable, later, you can store ‘Dinosaur’.

1. Python Variables Naming Rules

There are certain rules for what you can name a variable(called an identifier).

• Variables in Python can only begin with a letter(A-Z/a-z) or an underscore(_).

>>> 9lives=9

Output

>>> flag=0
>>> flag

>>> _9lives='cat'
>>> _9lives

Output

• The rest of the identifier may contain letters(A-Z/a-z), underscores(_), and numbers(0-9).

>>> year2='Sophomore'
>>> year2

Output

>>> _$$=7

Output

• Python is case-sensitive, and so are Python identifiers. Name and name are two different identifiers.

>>> name='Ayushi'
>>> name

Output

>>> Name

Output

• Reserved words (keywords) cannot be used as identifier names.

2. Assigning and Reassigning Python Variables

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

>>> age='Dinosaur'
>>> print(age)

Output

However, age=Dinosaur doesn’t make sense. Also, you cannot use Python variables before assigning it a value.

>>> name

Output

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

Neither can you assign Python variables to a keyword.

>>> False=choice

Output

3. Multiple Assignment

You can assign values to multiple Python variables in one statement.

>>> age,city=21,'Indore'
>>> print(age,city)

Output

Or you can assign the same value to multiple Python variables.

>>> age=fav=7
>>> print(age,fav)

Output

This is how you assign values to Python Variables

4. Swapping 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

5. Deleting Variables

You can also delete Python variables using the keyword ‘del’.

>>> a='red'
>>> del a
>>> a

Output

Python Data Types

Different kinds of data need different boxes. Python calls these kinds data types. The most common are numbers, text (called strings), lists, and True/False values (called booleans). Knowing the right type helps Python decide what actions are allowed.

You can check a variable’s type with the built-in type() function. If you mix the wrong types, Python shows an error. For smooth coding, always know what type you have and what type you need before you combine data.

Python supports the following data types.

1. Python Numbers

There are four numeric data types in Python.

a. int in Pythin

int stands for integer. The integer data type in Python holds signed integers. We can use the type() function to find which class it belongs to.

>>> a=-7
>>> type(a)

Output

An integer can be of any length, with the only limitation being the available memory.

>>> a=9999999999999999999999999999999
>>> type(a)

Output

b. float in Python

The float data type in Python holds floating-point real values. An int can only store the number 3, but a float can store 3.25 if you want.

>>> a=3.0
>>> type(a)

Output

c. long

Long Data type in Python holds a long integer of unlimited length. But this construct does not exist in Python 3.x.

d. complex

A complex data type in Python 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

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

2. Python Strings

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

>>> city="Ahmedabad"
>>> city

Output

a. Spanning a String Across Lines in Python

To span a string across multiple lines, you can use triple quotes.

>>> var="""If
only"""
>>> var

Output

>>> print(var)

Output

>>> """If
only"""

Output

As you can see, the quotes preserved the formatting (\n is the escape sequence for newline, \t is for tab).

b. Displaying Part of a String in Python

You can display a character from a string using its index in the string. Remember, indexing starts with 0.

>>> lesson='disappointment'
>>> lesson[0]

Output

You can also display a burst of characters in a string using the slicing operator [].

>>> lesson[5:10]

Output

This prints the characters from 5 to 9.

c. String Formatters in Python

String formatters in Python 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}")

d. String Concatenation in Python

You can concatenate(join) strings in Python.

>>> a='10'
>>> print(a+a)

Output

However, you cannot concatenate values of different types.

>>> print('10'+10)

Output

3. Python Lists

A list is a collection of values. Remember, it may contain different types of values.

To define a list in Python, you must put values separated by 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

a. Slicing a List in Python

You can slice a list in python the way you’d slice a string- with the slicing operator.

>>> days[1:3]

Output

Indexing for a list begins with 0, like for a string. Python doesn’t have arrays.

b. Finding the Length of a List in Python

Python supports an inbuilt function to calculate the length of a list.

>>> len(days)

Output

c. Reassigning Elements of a List

A list is mutable in Python. This means that you can reassign elements later on.

>>> days[2]='Wednesday'
>>> days

Output

d. Iterating on the List in Python

To iterate over the list in Python, 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 a list.

nums = [1,2,5,6,8]
for n in nums:
    print(n)

Output

e. Multidimensional Lists

A list may have more than one dimension. Have a detailed look at this in DataFlair’s tutorial on Python Lists.

>>> a=[[1,2,3],[4,5,6]]
>>> a

Output

4. Python Tuples

A tuple in Python is like a list. You declare it using parentheses instead.

>>> subjects=('Physics','Chemistry','Maths')
>>> subjects

Output

a. Accessing and Slicing a Tuple in Python

You access a tuple in Python the same way as you’d access a list. The same goes for slicing it.

>>> subjects[1]

Output

>>> subjects[0:2]

Output

b. A tuple is Immutable

Python tuple is immutable. Once declared, you can’t change its size or elements.

>>> subjects[2]='Biology'

Output

>>> subjects[3]='Computer Science'

Output

5. Python Dictionaries

A dictionary in Python 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

The type() function works with dictionaries too.

>>> type(person)

Output

a. Accessing a Value in a Dictionary

To access a value in a dictionary, you mention the key in square brackets.

>>> person['city']

Output

b. Reassigning Elements in Dictionary

You can reassign a value to a key.

>>> person['age']=21
>>> person['age']

Output

c. List of Keys

Use the keys() function to get a list of keys in the dictionary.

>>> person.keys()

Output

6. bool

A Boolean value can be True or False.

>>> a=2>1
>>> type(a)

Output

7. Python Sets

A set can have a list of values. In Python, a set is defined using curly braces.

>>> a={1,2,3}
>>> a

Output

It returns only one instance of any value present more than once.

>>> a={1,2,2,3}
>>> a

Output

However, a set is unordered, so it doesn’t support indexing.

>>> a[2]

Output

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

>>> a.remove(4)
>>> a

Output

>>> a.add(4)
>>> a

Output

Type Conversion in Python

Since Python is a dynamically-typed language, you may want to convert a value into another type. Python supports a list of functions for the same.

1. int() in Python

Python int() function converts the value into an int.

>>> int(3.7)

Output

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)

Output

>>> int(False)

However, you cannot turn a string into an int. It throws an error.

>>> int("a")

Output

However, if the string has only numbers, then you can.

>>> int("77")

Output

2. float() in Python

Python float() function converts the value into a float.

>>> float(7)

Output

>>> float(7.7)

Output

>>> float(True)

Output

>>> float("11")

Output

You can also use ‘e’ to denote an exponential number.

>>> float("2.1e-2")

Output

>>> float(2.1e-2)

Output

However, this number works even without the float() function.

>>> 2.1e-2

Output

3. str() in Python

Python str() function converts the value into a string.

>>> str(2.1)

Output

>>> str(7)

Output

>>> str(True)

Output

You can also convert a list, a tuple, a set, or a dictionary into a string.

>>> str([1,2,3])

Output

4. bool() in Python

Python bool() function converts the value into a boolean.

>>> bool(3)

Output

>>> bool(0)

Output

>>> bool(True)

Output

>>> bool(0.1)

Output

You can convert a list into a Boolean.

>>> bool([1,2])

Output

The function returns False for empty constructs.

>>> bool()

Output

>>> bool([])

Output

>>> bool({})

Output

None is a keyword in Python that represents an absence of value.

>>> bool(None)

Output

5. set() in Python

python set() function converts the value into a set.

>>> set([1,2,2,3])

Output

>>> set({1,2,2,3})

Output

6. list() in Python

Python list() function converts the value into a list.

>>> del list
>>> list("123")

Output

>>> list({1,2,2,3})

Output

>>> list({"a":1,"b":2})

Output

However, the following raises an error.

>>> list({a:1,b:2})

Output

7. tuple() in Python

Python tuple() function converts the value into a tuple.

>>> tuple({1,2,2,3})

Output

You can try your own combinations. Also, try composite functions.

>>> tuple(list(set([1,2])))

Output

Python Local and Global Variables

Another classification of Python variables is based on scope.

1. Python Local Variables

When you declare a variable in a function, class, or so on, it is only visible in that scope. If you call it outside of that scope, you get an ‘undefined’ error.

• Local variables in Python can be accessed only within a particular function.
• It executes when a function is called in which the local variable is defined.

>>> def func1():
	uvw=2
	print(uvw)
>>> func1()

Output

2

>>> uvw

Output

Here, the variable uvw is local to the function func1().

2. Global Variables in Python

When you declare a variable outside any context/scope, it is visible in the whole program.

• It can be accessed anywhere in the entire program.
• If the value of a global variable is changed, it will affect the whole program.

>>> xyz=3
>>> def func2():
	xyz=0
	xyz+=1
	print(xyz)
>>> func2()

Output

>>> xyz

Output

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

>>> foo

Output

Frequently asked Python Interview Questions on Python Variables and Datatypes?