Python Variables

In Python, variables are used to store data that can be referenced and manipulated during program execution. A variable is essentially a name that is assigned to a value.

• Unlike Java and many other languages, Python variables do not require explicit declaration of type.
• The type of the variable is inferred based on the value assigned.

x = 5
name = "Samantha"  
print(x)
print(name)

Output:

5

Samantha

Rules for Naming Variables

To use variables effectively, we must follow Python’s naming rules:

• Variable names can only contain letters, digits and underscores (_).
• A variable name cannot start with a digit.
• Variable names are case-sensitive like myVar and myvar are different.
• Avoid using Python keywords like if, else, for as variable names.

Valid :

age = 21
_colour = "lilac"
total_score = 90

Invalid :

1name = "Error"  # Starts with a digit
class = 10       # 'class' is a reserved keyword
user-name = "Doe"  # Contains a hyphen

Assigning Values to Variables

Basic Assignment

Variables in Python are assigned values using the = operator.

x = 5
y = 3.14
z = "Hi"

Dynamic Typing

Python variables are dynamically typed, meaning the same variable can hold different types of values during execution.

x = 10
x = "Now a string"

Multiple Assignments

Python allows multiple variables to be assigned values in a single line.

Assigning the Same Value

Python allows assigning the same value to multiple variables in a single line, which can be useful for initializing variables with the same value.

a = b = c = 100
print(a, b, c) 

Output:

100 100 100

Assigning Different Values

We can assign different values to multiple variables simultaneously, making the code concise and easier to read.

x, y, z = 1, 2.5, "Python"
print(x, y, z) 

Output:

1 2.5 Python

Type Casting a Variable

Type casting refers to the process of converting the value of one data type into another. Python provides several built-in functions to facilitate casting, including int(), float() and str() among others.

Basic Casting Functions

• int(): Converts compatible values to an integer.
• float(): Transforms values into floating-point numbers.
• str(): Converts any data type into a string.

s = "10"  
n = int(s) 
cnt = 5
f = float(cnt)  
age = 25
s2 = str(age)  

print(n)  
print(f)  
print(s2)  

Output:

10

5.0

25

Getting the Type of Variable

In Python, we can determine the type of a variable using the type() function. This built-in function returns the type of the object passed to it.

n = 42
f = 3.14
s = "Hello, World!"
li = [1, 2, 3]
d = {'key': 'value'}
bool = True

print(type(n))   
print(type(f)) 
print(type(s))   
print(type(li))     
print(type(d))     
print(type(bool))  

Output:

<class 'int'>

<class 'float'>

<class 'str'>

<class 'list'>

<class 'dict'>

<class 'bool'>

Object Reference in Python

Let us assign a variable x to value 5.

x = 5

When x = 5 is executed, Python creates an object to represent the value 5 and makes x reference this object.

Now, let's assign another variable y to the variable x.

y = x

• Python encounters the first statement, it creates an object for the value 5 and makes x reference it. The second statement creates y and references the same object as x, not x itself. This is called a Shared Reference, where multiple variables reference the same object.

Now, if we write

x = 'Geeks'

Python creates a new object for the value "Geeks" and makes x reference this new object.

The variable y remains unchanged, still referencing the original object 5.

If we now assign a new value to y:

y = "Computer"

• Python creates yet another object for "Computer" and updates y to reference it.
• The original object 5 no longer has any references and becomes eligible for garbage collection.
• Python variables hold references to objects, not the actual objects themselves.
• Reassigning a variable does not affect other variables referencing the same object unless explicitly updated.

Delete a Variable Using del Keyword

We can remove a variable from the namespace using the del keyword. This deletes the variable and frees up the memory it was using.

x = 10
print(x) 
del x
# Trying to print x after deletion will raise an error
# print(x)  # Uncommenting this line will raise NameError: name 'x' is not defined

• del x removes the variable x from memory.
• After deletion, trying to access the variable x results in a NameError indicating that the variable no longer exists.

Practical Examples

1. Swapping Two Variables

Using multiple assignments, we can swap the values of two variables without needing a temporary variable.

a, b = 5, 10
a, b = b, a
print(a, b)  

Output:

10 5

2. Counting Characters in a String

Assign the results of multiple operations on a string to variables in one line.

word = "Python"
length = len(word)
print("Length of the word:", length) 

Output:

Length of the word: 6

Related Posts:

• Python Variable Quiz
• Local and Global Scope
• Assign function to a Variable in Python
• Insert a Variable into a String in Python
• Type Casting in Python

Recommended Problems:

• Type Conversion
• TypeCast And Double It
• Swap The Numbers
• Sum of N Numbers
• Int Str

Variables in Python

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