Python Variable is containers that store values. Python is not “statically typed”. We do not need to declare variables before using them or declare their type. A variable is created the moment we first assign a value to it. A Python variable is a name given to a memory location. It is the basic unit of storage in a program.
Example of Variable in Python
An Example of a Variable in Python is a representational name that serves as a pointer to an object. Once an object is assigned to a variable, it can be referred to by that name. In layman’s terms, we can say that Variable in Python is containers that store values.
Here we have stored “Geeksforgeeks” in a var which is variable, and when we call its name the stored information will get printed.
Python3
Var = "Geeksforgeeks"
print(Var)
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Output:
Geeksforgeeks
Notes:
- The value stored in a variable can be changed during program execution.
- A Variables in Python is only a name given to a memory location, all the operations done on the variable effects that memory location.
Rules for Python variables
- A Python variable name must start with a letter or the underscore character.
- A Python variable name cannot start with a number.
- A Python variable name can only contain alpha-numeric characters and underscores (A-z, 0-9, and _ ).
- Variable in Python names are case-sensitive (name, Name, and NAME are three different variables).
- The reserved words(keywords) in Python cannot be used to name the variable in Python.
Example
Python3
geeks = 1
Geeks = 2
Ge_e_ks = 5
_geeks = 6
geeks_ = 7
_GEEKS_ = 8
print(geeks, Geeks, Ge_e_ks)
print(_geeks, geeks_, _GEEKS_)
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Output:
1 2 5
6 7 8
Variables Assignment in Python
Here, we have assigned a number, a floating point number, and a string to a variable such as age, salary, and name.
Python3
age = 45
salary = 1456.8
name = "John"
print(age)
print(salary)
print(name)
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Output:
45
1456.8
John
Declaration and Initialization of Variables
Let’s see how to declare the variable and print the variable.
Python3
Number = 100
print( Number)
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Output:
100
Redeclaring variables in Python
We can re-declare the Python variable once we have declared the variable already.
Python3
Number = 100
print("Before declare: ", Number)
Number = 120.3
print("After re-declare:", Number)
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Output:
Before declare: 100
After re-declare: 120.3
Python Assign Values to Multiple Variables
Also, Python allows assigning a single value to several variables simultaneously with “=” operators.
For example:
Python3
a = b = c = 10
print(a)
print(b)
print(c)
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Output:
10
10
10
Assigning different values to multiple variables
Python allows adding different values in a single line with “,” operators.
Python3
a, b, c = 1, 20.2, "GeeksforGeeks"
print(a)
print(b)
print(c)
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Output:
1
20.2
GeeksforGeeks
Can we use the same name for different types?
If we use the same name, the variable starts referring to a new value and type.
Python3
a = 10
a = "GeeksforGeeks"
print(a)
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Output:
GeeksforGeeks
How does + operator work with variables?
The Python plus operator + provides a convenient way to add a value if it is a number and concatenate if it is a string. If a variable is already created it assigns the new value back to the same variable.
Python3
a = 10
b = 20
print(a+b)
a = "Geeksfor"
b = "Geeks"
print(a+b)
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Can we use + for different Datatypes also?
No use for different types would produce an error.
Python3
a = 10
b = "Geeks"
print(a+b)
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Output :
TypeError: unsupported operand type(s) for +: 'int' and 'str'
Global and Local Python Variables
Local variables in Python are the ones that are defined and declared inside a function. We can not call this variable outside the function.
Python3
def f():
s = "Welcome geeks"
print(s)
f()
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Output:
Welcome geeks
Global variables in Python are the ones that are defined and declared outside a function, and we need to use them inside a function.
Python3
def f():
print(s)
s = "I love Geeksforgeeks"
f()
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Output:
I love Geeksforgeeks
Global keyword in Python
Python global is a keyword that allows a user to modify a variable outside of the current scope. It is used to create global variables from a non-global scope i.e inside a function. Global keyword is used inside a function only when we want to do assignments or when we want to change a variable. Global is not needed for printing and accessing.
Rules of global keyword
- If a variable is assigned a value anywhere within the function’s body, it’s assumed to be local unless explicitly declared as global.
- Variables that are only referenced inside a function are implicitly global.
- We use a global in Python to use a global variable inside a function.
- There is no need to use a global keyword in Python outside a function.
Example:
Python program to modify a global value inside a function.
Python3
x = 15
def change():
global x
x = x + 5
print("Value of x inside a function :", x)
change()
print("Value of x outside a function :", x)
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Output:
Value of x inside a function : 20
Value of x outside a function : 20
Variable Types in Python
Data types are the classification or categorization of data items. It represents the kind of value that tells what operations can be performed on a particular data. Since everything is an object in Python programming, data types are actually classes and variables are instances (object) of these classes.
Built-in Python Data types are:
Example:
In this example, we have shown different examples of Built-in data types in Python.
Python3
var = 123
print("Numeric data : ", var)
String1 = 'Welcome to the Geeks World'
print("String with the use of Single Quotes: ")
print(String1)
print(type(True))
print(type(False))
set1 = set("GeeksForGeeks")
print("\nSet with the use of String: ")
print(set1)
Dict = {1: 'Geeks', 2: 'For', 3: 'Geeks'}
print("\nDictionary with the use of Integer Keys: ")
print(Dict)
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Output:
Numeric data : 123
String with the use of Single Quotes:
Welcome to the Geeks World
<class 'bool'>
<class 'bool'>
Set with the use of String:
{'r', 'G', 'e', 'k', 'o', 's', 'F'}
Dictionary with the use of Integer Keys:
{1: 'Geeks', 2: 'For', 3: 'Geeks'}Object Reference in Python
Let us assign a variable x to value 5.
x = 5
Another variable is y to the variable x.
y = x
When Python looks at the first statement, what it does is that, first, it creates an object to represent the value 5. Then, it creates the variable x if it doesn’t exist and made it a reference to this new object 5. The second line causes Python to create the variable y, and it is not assigned with x, rather it is made to reference that object that x does. The net effect is that the variables x and y wind up referencing the same object. This situation, with multiple names referencing the same object, is called a Shared Reference in Python.
Now, if we write:
x = 'Geeks'
This statement makes a new object to represent ‘Geeks’ and makes x reference this new object.
Now if we assign the new value in Y, then the previous object refers to the garbage values.
y = "Computer"
Creating objects (or variables of a class type)
Please refer to Class, Object, and Members for more details.
Python3
class CSStudent:
stream = 'cse'
def __init__(self, roll):
self.roll = roll
a = CSStudent(101)
b = CSStudent(102)
print(a.stream)
print(b.stream)
print(a.roll)
print(CSStudent.stream)
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