Python Variable
Variable and Value
- A variable is a named memory location where data can be stored. For example: roll_no, amount, name.
- A value is the data stored in a variable, which can be a string, numeric value, etc. For example: "Sara", 120, 25.36.
Key Points About Python Variables:
- Variables are created when they are first assigned a value.
- They must be assigned before being referenced.
- The value stored in a variable can be accessed or updated later.
- No declaration is required before using a variable.
- The type of the variable (e.g., string, int, float) is determined automatically by Python based on the value assigned.
- Python manages memory allocation based on the data type of the variable.
Python Variable Name Rules
- Must begin with a letter (a-z, A-Z) or an underscore (_).
- Subsequent characters can be letters, numbers, or underscores.
- Case-sensitive: age, Age, and AGE are considered different variables.
- Can be of any reasonable length.
- Reserved words (like if, for, while, etc.) cannot be used as variable names.
Good Variable Naming Practices
- Choose meaningful names, such as roll_no, which is clearer than rn.
- Avoid unnecessarily long variable names (e.g., Roll_no_of_a_student is too long).
- Be consistent in your naming convention: roll_no or RollNo, but not both.
- Start variable names with an underscore (_) when you need a special case or private variables.
Python Assignment Statements
Assignment statements create variables and assign values to them. The basic syntax for an assignment is:
Syntax:
<variable> = <expr>
Where the equal sign (=) is used to assign value (right side) to a variable name (left side). See the following statements :
>>> Item_name = "Computer" #A String
>>> Item_qty = 10 #An Integer
>>> Item_value = 1000.23 #A floating point
>>> print(Item_name)
Computer
>>> print(Item_qty)
10
>>> print(Item_value)
1000.23
>>>
Note: Assignment reads right to left. This is why a = 12 works, but 12 = a results in a syntax error.
Example:
a = 12 is correct, but 12 = a does not make sense to Python, which creates a syntax error. Check it in Python Shell.
>>> a = 12
>>> 12 = a
SyntaxError: can't assign to literal
>>>
Multiple Assignment
The basic assignment statement works for a single variable and a single expression. You can also assign a single value to more than one variables simultaneously.
Syntax:
var1=var2=var3...varn= = <expr>
Example:
x = y = z = 1
Now check the individual value in Python Shell.
>>> x = y = z = 1
>>> print(x)
1
>>> print(y)
1
>>> print(z)
1
>>>
Alternatively, you can assign multiple values to multiple variables in a single line.
Syntax:
<var>, <var>, ..., <var> = <expr>, <expr>, ..., <expr>
Example:
x, y, z = 1, 2, "abcd"
In the above example x, y and z simultaneously get the new values 1, 2 and "abcd".
>>> x,y,z = 1,2,"abcd"
>>> print(x)
1
>>> print(y)
2
>>> print(z)
abcd
You can reuse variable names by simply assigning a new value to them :
>>> x = 100
>>> print(x)
100
>>> x = "Python"
>>> print(x)
Python
>>>
Other ways to define value
Python allows formatting of large numbers and decimal values for better readability.
>>> five_millions = 5_000_000
>>> five_millions
Output:
5000000
>>> small_int = .35
>>> small_int
Output:
0.35
>>> c_thousand = 10e3
>>> c_thousand
Output:
10000.0
Swap variables
In Python, you can swap the values of two variables in a single line.
Syntax:
var1, var2 = var2, var1
Example:
>>> x = 10
>>> y = 20
>>> print(x)
10
>>> print(y)
20
>>> x, y = y, x
>>> print(x)
20
>>> print(y)
10
>>>
Local and global variables in Python
- Global variables are accessible throughout the entire program, even within functions.
- Local variables are defined within a function and cannot be accessed outside it.
- A variable is assumed to be local unless explicitly declared as global using the global keyword.
Example:
var1 = "Python"
def func1():
var1 = "PHP"
print("In side func1() var1 = ",var1)
def func2():
print("In side func2() var1 = ",var1)
func1()
func2()
Output:
In side func1() var1 = PHP In side func2() var1 = Python
You can use a global variable in other functions by declaring it as global keyword :
Example:
def func1():
global var1
var1 = "PHP"
print("In side func1() var1 = ",var1)
def func2():
print("In side func2() var1 = ",var1)
func1()
func2()
Output:
In side func1() var1 = PHP In side func2() var1 = PHP
Previous: Python Syntax
Next: Python Data Type
Test your Python skills with w3resource's quiz
It will be nice if you may share this link in any developer community or anywhere else, from where other developers may find this content. Thanks.
https://198.211.115.131/python/python-variable.php
- Weekly Trends and Language Statistics
- Weekly Trends and Language Statistics