
Absolutely! Here's a detailed tutorial-style article on Python Variables including explanations, code snippets, examples, tips, and common mistakes.
Understanding Variables in Python
Variables are one of the most fundamental concepts in programming. In Python, variables are used to store data that can be referenced and manipulated later in the program.
This article will guide you through what variables are, how they work in Python, and best practices for using them effectively.
What is a Variable?
A variable is a name that refers to a value. Think of it like a container that holds data.
✅ Syntax:
variable_name = value
Python uses the equals sign (=
) as the assignment operator.
Example:
name = "Alice"
age = 30
height = 5.9
is_student = True
Here, Python:
-
Creates a variable
name
and stores a string"Alice"
in it. -
Creates
age
and stores an integer. -
Stores a float in
height
. -
Stores a boolean in
is_student
.
Dynamic Typing in Python
Python is dynamically typed, which means:
-
You don’t need to declare the type.
-
Variables can change type at runtime.
x = 10 # x is an integer
x = "hello" # now x is a string
Variable Naming Rules
-
Must start with a letter (a–z, A–Z) or an underscore (
_
) -
Can contain letters, numbers, and underscores
-
Cannot start with a number
-
Case-sensitive (
name
,Name
, andNAME
are different)
✅ Valid Names:
username = "admin"
_user1 = 5
total_amount = 100.0
❌ Invalid Names:
1name = "John" # Starts with number
user-name = "Sam" # Hyphen not allowed
Variable Types (Built-in)
Here are some common data types used in Python variables:
Type | Example | Description |
---|---|---|
int |
x = 10 |
Integer |
float |
x = 3.14 |
Decimal numbers |
str |
x = "Hello" |
Text (string) |
bool |
x = True |
Boolean (True/False) |
list |
x = [1, 2, 3] |
List (array) |
dict |
x = {"key": "value"} |
Dictionary |
NoneType |
x = None |
Represents absence of value |
Assigning Multiple Variables
Python supports multiple assignment in one line:
Example:
x, y, z = 1, 2, 3
print(x, y, z) # Output: 1 2 3
You can also assign the same value to multiple variables:
a = b = c = 0
Checking Variable Type
Use the built-in type()
function:
name = "Alice"
print(type(name)) # Output: <class 'str'>
Example: Simple User Profile
# Define user information
name = "Alice"
age = 28
height = 5.6
is_member = True
# Print a profile
print("User Profile")
print("Name:", name)
print("Age:", age)
print("Height:", height, "ft")
print("Membership:", is_member)
Tips for Working with Variables
-
Use descriptive names like
user_age
instead of justx
-
Reuse variables thoughtfully, but don’t overdo it
-
Avoid using Python keywords (e.g.,
if
,for
,def
) as variable names -
Always test your variable values using
print()
ortype()
when debugging
⚠️ Common Mistakes and Pitfalls
Mistake | Example | Fix |
---|---|---|
Using undefined variables | print(score) before assigning |
Always assign before use |
Case-sensitivity confusion | Name != name |
Use consistent naming |
Using Python keywords | def = 5 |
Rename variable |
Type confusion | age = "25" vs age = 25 |
Convert types explicitly if needed |
Shadowing built-in names | list = [1, 2, 3] |
Avoid overwriting built-ins |
Summary
-
Variables store data and are created using the assignment operator
=
-
Python is dynamically typed — variable types can change
-
Use clear and descriptive variable names
-
Check types using
type()
-
Avoid common mistakes like using reserved words or uninitialized variables
Tips and Tricks
What is pass in Python?
Python | Pass Statement
The pass statement is used as a placeholder for future code. It represents a null operation in Python. It is generally used for the purpose of filling up empty blocks of code which may execute during runtime but has yet to be written.
def myfunction():
pass
How can you generate random numbers?
Python | Generate random numbers
Python provides a module called random using which we can generate random numbers. e.g: print(random.random())
We have to import a random module and call the random() method as shown below:
import random
print(random.random())
The random() method generates float values lying between 0 and 1 randomly.
To generate customized random numbers between specified ranges, we can use the randrange() method
Syntax: randrange(beginning, end, step)
import random
print(random.randrange(5,100,2))
What is lambda in Python?
Python | Lambda function
A lambda function is a small anonymous function. This function can have any number of parameters but, can have just one statement.
Syntex:
lambda arguments : expression
a = lambda x,y : x+y
print(a(5, 6))
It also provides a nice way to write closures. With that power, you can do things like this.
def adder(x):
return lambda y: x + y
add5 = adder(5)
add5(1) #6
As you can see from the snippet of Python, the function adder takes in an argument x and returns an anonymous function, or lambda, that takes another argument y. That anonymous function allows you to create functions from functions. This is a simple example, but it should convey the power lambdas and closures have.
What is swapcase() function in the Python?
Python | swapcase() Function
It is a string's function that converts all uppercase characters into lowercase and vice versa. It automatically ignores all the non-alphabetic characters.
string = "IT IS IN LOWERCASE."
print(string.swapcase())
How to remove whitespaces from a string in Python?
Python | strip() Function | Remove whitespaces from a string
To remove the whitespaces and trailing spaces from the string, Python provides a strip([str]) built-in function. This function returns a copy of the string after removing whitespaces if present. Otherwise returns the original string.
string = " Python "
print(string.strip())
What is the usage of enumerate() function in Python?
Python | enumerate() Function
The enumerate() function is used to iterate through the sequence and retrieve the index position and its corresponding value at the same time.
lst = ["A","B","C"]
print (list(enumerate(lst)))
#[(0, 'A'), (1, 'B'), (2, 'C')]
Can you explain the filter(), map(), and reduce() functions?
Python | filter(), map(), and reduce() Functions
- filter() function accepts two arguments, a function and an iterable, where each element of the iterable is filtered through the function to test if the item is accepted or not.
>>> set(filter(lambda x:x>4, range(7))) # {5, 6}
-
map() function calls the specified function for each item of an iterable and returns a list of result
>>> set(map(lambda x:x**3, range(7))) # {0, 1, 64, 8, 216, 27, 125}
-
reduce() function reduces a sequence pair-wise, repeatedly until we arrive at a single value..
>>> reduce(lambda x,y:y-x, [1,2,3,4,5]) # 3
Let’s understand this:
2-1=1
3-1=2
4-2=2
5-2=3Hence, 3.
What is a namedtuple?
Python | namedtuple
A namedtuple will let us access a tuple’s elements using a name/label. We use the function namedtuple() for this, and import it from collections.
>>> from collections import namedtuple
#format
>>> result=namedtuple('result','Physics Chemistry Maths')
#declaring the tuple
>>> Chris=result(Physics=86,Chemistry=92,Maths=80)
>>> Chris.Chemistry
# 92
Write a code to add the values of same keys in two different dictionaries and return a new dictionary.
We can use the Counter method from the collections module
from collections import Counter
dict1 = {'a': 5, 'b': 3, 'c': 2}
dict2 = {'a': 2, 'b': 4, 'c': 3}
new_dict = Counter(dict1) + Counter(dict2)
print(new_dict)
# Print: Counter({'a': 7, 'b': 7, 'c': 5})
Python In-place swapping of two numbers
Python | In-place swapping of two numbers
>>> a, b = 10, 20
>>> print(a, b)
10 20
>>> a, b = b, a
>>> print(a, b)
20 10
Reversing a String in Python
Python | Reversing a String
>>> x = 'PythonWorld'
>>> print(x[: : -1])
dlroWnohtyP
Python join all items of a list to convert into a single string
Python | Join all items of a list to convert into a single string
>>> x = ["Python", "Online", "Training"]
>>> print(" ".join(x))
Python Online Training
python return multiple values from functions
Python | Return multiple values from functions
>>> def A():
return 2, 3, 4
>>> a, b, c = A()
>>> print(a, b, c)
2 3 4
Python Print String N times
Python | Print String N times
>>> s = 'Python'
>>> n = 5
>>> print(s * n)
PythonPythonPythonPythonPython
Python check the memory usage of an object
Python | Check the memory usage of an object
>>> import sys
>>> x = 100
>>> print(sys.getsizeof(x))
28