Variables are one of the first concepts you must understand to write real programs. In Python, a variable is simply a name that points to a value in memory. You can think of it as a label you attach to data so you can reuse it later.
This lesson walks you through how to create variables, the rules for naming them, and the most common Python data types you’ll use right away.
In Python, you create a variable using the assignment operator: =
x = 5Here, = means: store the value ** in the variable named **.
In a Jupyter Notebook, you can run a cell by pressing Shift + Enter.
[Running a notebook cell using Shift + Enter]
You can display a variable in two common ways:
print():x = 5
print(x)Code language: PHP (php)x = 5
xIn Jupyter, the last expression of a cell is displayed automatically.
[Jupyter auto-displays the last line of a cell]
Python also lets you assign multiple values in a single line. This is useful when you’re working with related pieces of data.
a, b, c = 1, 2, 3
print(a)
print(b)
print(c)Code language: PHP (php)Each variable on the left matches the value in the same position on the right.
x = y = z = 0This sets x, y, and z to 0.
A very common pattern is swapping two variables without a temporary variable:
a = 10
b = 20
a, b = b, aAfter this, a becomes 20 and b becomes 10.
[Multiple assignment and swapping values]
So far, we’ve been creating variables at the top level of the notebook (outside of any function). In Python, those are often called global variables—meaning they’re available throughout your notebook (as long as the cell that defines them has been run).
Once you start writing functions, Python introduces an important idea called scope:
Here’s a simple example that shows the difference:
x = 5
def demo():
x = 10 # local to the function
print(x)
demo()
print(x)
Code language: PHP (php)This prints 10 from inside the function, and then prints 5 outside—because the x inside the function is a different, local variable.
If you truly need to update a global variable from inside a function, you can use the global keyword:
counter = 0
def increment():
global counter
counter = counter + 1
increment()
counter
Code language: PHP (php)Using global variables too much can make programs harder to understand and debug. As you progress, you’ll usually prefer passing values into functions and returning results.
Global vs local variables (scope) example]
While working through this course, you’ll create and run many small cells.
[Inserting a cell above using the A key]
Python is strict about variable names. If you break the rules, Python won’t understand your code and will raise a SyntaxError.
x1 = 10
user_name = "Ryan"
age = 25
Code language: JavaScript (javascript)A variable name cannot start with a number:
1x = 10
That will cause a syntax error because Python doesn’t treat something like 1x as a valid name.
Variable names also can’t contain most special characters (like @, #, !, -). The underscore _ is the common exception.
Python allows uppercase letters in names, but by convention, most variables start with lowercase:
name = "Ryan"
Code language: JavaScript (javascript)Starting names with uppercase can be confusing later because uppercase names are often used for things like classes (you’ll learn those later). Following the convention keeps your code readable and consistent.
[Screenshot: Example of valid vs invalid variable names]
Every value in Python has a type. The type tells Python what kind of data it is and what operations are allowed.
type()Python gives you a built-in function to check a value’s type:
x = 5
type(x)
Try it with a string:
name = "Ryan"
type(name)
Code language: JavaScript (javascript)[ Using type() in a notebook]
int, float, complexint) — whole numbersIntegers are whole numbers without a decimal point.
count = 3
price = 100
type(count)
float) — decimal numbersFloats are numbers with decimals.
rating = 4.5
pi = 3.14159
You might also see floats written like .9 (which is the same as 0.9).
x = 0.9
y = .9
x, y
The term “float” comes from how computers store decimal numbers—the decimal point position can effectively “float.”
[ Examples of int and float values]
complex) — advanced math valuesPython also supports complex numbers, which include an imaginary part. In many math textbooks the imaginary unit is written as i, but Python uses j.
z = 2j
type(z)
You can do arithmetic with complex numbers too:
1j * 1j
This results in -1+0j (which is basically -1).
[ Complex number examples]
strText in Python is stored as a string (a sequence of characters). Strings are written inside quotes.
name = "Ryan"
message = "Hello, Python!"
Code language: JavaScript (javascript)You can use single quotes too, but throughout this tutorial series, we’ll prefer double quotes for consistency.
You can join strings using +:
first = "Hello"
second = "World"
first + " " + second
Code language: JavaScript (javascript)If you add two string numbers, Python still treats them as text:
"1" + "1"
Code language: JavaScript (javascript)This gives "11", not 2, because Python is concatenating characters.
If you try to add a string and an integer:
"1" + 1
Code language: JavaScript (javascript)Python raises a TypeError, explaining that it can’t concatenate a string and an integer. When you get errors in Python, it’s important to read them—most of the time, Python tells you what types it expected.
[ Example TypeError for string + int]
boolBooleans represent logical values: True and False.
is_active = True
is_admin = False
Code language: PHP (php)Notice the capital letters. If you write true or false in lowercase, Python treats them as variable names and throws an error because those variables don’t exist.
true # NameError (not defined)
Code language: PHP (php)[ True/False capitalization example]
list, tuple, rangeA sequence stores values in order.
A list is the most common sequence. It’s mutable, meaning you can change it after creating it:
nums = [1, 2, 3]
nums.append(4)
nums
A tuple is like a list, but it’s immutable (great for fixed collections like coordinates):
point = (10, 20)
type(point)
A range represents a sequence of numbers and is often used in loops. It’s memory-efficient because it doesn’t store every number upfront:
r = range(5)
list(r) # convert to a list to see the values
Code language: PHP (php)[ list vs tuple vs range examples]
dictA dict (dictionary) stores key → value pairs, which is perfect when you want to look up information by a label (like a name, id, or code).
student = {"name": "Ryan", "age": 25}
student["name"]
Code language: JavaScript (javascript)[Accessing values from a dict]
set, frozensetA set stores unique items (duplicates are automatically removed). This is useful for removing duplicates or checking membership.
tags = {"python", "data", "python"}
tags
Code language: JavaScript (javascript)A frozenset is an immutable set.
fixed_tags = frozenset(["python", "ml"])
type(fixed_tags)
Code language: JavaScript (javascript)[Screenshot: set vs frozenset example]
NoneTypePython has a special value called None that represents “no value” or “not set yet.” It’s commonly used as a default value, a placeholder, or a function return when there’s nothing meaningful to return.
result = None
type(result)
When you check the type, you’ll see NoneType.
[None and NoneType example]
bytes, bytearray, memoryviewThese types are used when working with raw binary data (common in file handling, images, audio, and network requests).
bytes is an immutable sequence of bytes.bytearray is a mutable version of bytes.memoryview lets you view and slice binary data efficiently without copying it.data = b"ABC" # bytes
mutable = bytearray(b"ABC") # bytearray
view = memoryview(data) # memoryview
data, mutable, view[0]
Code language: PHP (php)[bytes, bytearray, and memoryview example]
=) vs Comparison (==)This is one of the most important early distinctions.
= is assignmentIt stores a value in a variable:
x = 5
== is comparisonIt checks whether two values are equal and returns a boolean:
1 == 1
This returns True.
1 == 2
This returns False.
So remember:
= puts a value into a variable== compares two values[ Comparing values using ==]
Type these into a notebook and run them one by one. Don’t rush—focus on understanding the output.
x = 10
print(x)
Code language: PHP (php)name = "Asha"
print("Hello, " + name)
Code language: PHP (php)a = "2"
b = "3"
print(a + b) # what do you expect?
Code language: PHP (php)n = 2
m = 3
print(n + m) # compare with the previous result
Code language: PHP (php)print(type(3))
print(type(3.0))
print(type("3"))
Code language: PHP (php)print(5 == 5)
print(5 == 6)
Code language: PHP (php)You don’t need to memorize everything in one go. The most important takeaway is that variables are the foundation of every program, and Python types control what you can do with your data.
As you write more code, these concepts will keep coming back—so the goal here is familiarity and confidence, not perfection on day one.