Python Variables: Declaring and Managing String Types

What Is a Variable in Python?

A Python variable is a reserved memory location that stores a value. In a program, a variable supplies data to the computer for processing.

Python Variable Types

Every value in Python has a datatype—numbers, lists, tuples, strings, dictionaries, and more. Variable names can be any valid identifier such as a, aa, or abc.

How to Declare and Use a Variable

Below is a simple example that declares a variable a and prints its value.

a=100
print(a)

Re‑Declare a Variable

Python lets you re‑assign a variable after it has been created. The following examples demonstrate this in both Python 2 and Python 3.

Python 2:

# Initial declaration
f = 0
print f
# Re‑assignment
f = 'guru99'
print f

Python 3:

# Initial declaration
f = 0
print(f)
# Re‑assignment
f = 'guru99'
print(f)

String Concatenation with Variables

Unlike Java, Python does not automatically convert numbers to strings during concatenation. Attempting to concatenate a string and an integer raises a TypeError. Convert the number to a string first:

a='Guru'
b=99
print(a+str(b))  # Outputs: Guru99

Local vs. Global Variables

Variables can be either local (limited to a function) or global (accessible throughout the module). The following examples illustrate the difference.

Python 2 (without the global keyword):

f = 101
print f

def someFunction():
    f = 'I am learning Python'
    print f

someFunction()
print f

Python 3 (without the global keyword):

f = 101
print(f)

def someFunction():
    f = 'I am learning Python'
    print(f)

someFunction()
print(f)

Using the global keyword allows a function to modify a global variable:

Python 2:

f = 101
print f

def someFunction():
    global f
    print f
    f = 'changing global variable'

someFunction()
print f

Python 3:

f = 101
print(f)

def someFunction():
    global f
    print(f)
    f = 'changing global variable'

someFunction()
print(f)

Deleting a Variable

To remove a variable from memory, use the del keyword. After deletion, accessing the variable raises a NameError:

f = 11
print(f)

del f
print(f)  # Raises NameError

Summary

• Variables act as named storage locations for data.
• They can be named using any valid identifier.
• Python allows variables to be reassigned to new values.
• String concatenation requires explicit conversion of non‑string types.
• Local variables are confined to functions; global variables are accessible module‑wide.
• Use the global keyword to modify a global variable inside a function.
• The del keyword deletes a variable from the namespace.