Python Basics: Syntax, Variables, Types & Control Flow

Master Python’s core syntax, variable model, data types, operators, and control-flow constructs to confidently write your first programs.

Python is a high-level, interpreted, object-oriented programming language celebrated for its clean syntax and remarkable readability. Before you write your first FastAPI endpoint or train your first AI model, you need a firm grip on Python’s fundamentals — how variables work, how data is typed, how operators behave, and how execution flows through your programs. This page walks you through every building block you need, with concrete examples and the nuances that trip up beginners.

Python Fundamentals

A few key characteristics distinguish Python from other languages:

• Python is dynamically typed — you never declare a variable’s type explicitly.
• Python uses indentation instead of curly braces {} to define code blocks.
• Everything in Python is an object, including functions and classes.
• Variables store references to objects, not the objects themselves.
• Python follows the PEP 8 style guide for consistent, readable code.

Variables

Variables store references to objects in memory. You create them simply by assigning a value.

name = "Alice"
age = 20
price = 99.99
is_active = True

Multiple Assignment

Python lets you assign several variables in one line:

x, y, z = 10, 20, 30

Variable Swapping

Swapping two values requires no temporary variable in Python:

a, b = 10, 20
a, b = b, a
print(a, b)  # 20 10

Object Identity

Two variables can reference the same underlying object:

a = [1, 2]
b = a

print(a == b)   # True  — same value
print(a is b)   # True  — same object in memory

Use == to compare values and is to compare object identity. Never use is to compare numbers or strings in regular code.

Everything is an Object

In Python, every value — number, string, list, function, class — is a first-class object with a type and a unique identity:

x = 10
print(type(x))   # <class 'int'>
print(id(x))     # Memory address of the object

Small Integer Caching

CPython caches integers in the range -5 to 256 as a performance optimisation. This means two variables assigned the same small integer may point to the identical object:

a = 100
b = 100
print(a is b)   # True  (cached)

x = 1000
y = 1000
print(x is y)   # May be False (not cached)

Floating-Point Precision

Floats are stored in binary, so some decimal values cannot be represented exactly:

print(0.1 + 0.2)           # 0.30000000000000004
print(0.1 + 0.2 == 0.3)    # False

Use round() or math.isclose() when comparing floating-point numbers to avoid precision surprises.

Data Types

Python provides a rich set of built-in types:

Category	Types
Numeric	int, float, complex
Boolean	bool
Text	str
Sequence	list, tuple, range
Mapping	dict
Set	set, frozenset
Binary	bytes, bytearray
Special	None

print(type(10))            # <class 'int'>
print(type(3.14))          # <class 'float'>
print(type("Hello"))       # <class 'str'>
print(type([1, 2, 3]))     # <class 'list'>
print(type({"name": "Alice"}))  # <class 'dict'>

Type Conversion

Convert between types using built-in functions:

int("10")          # 10
float("3.14")      # 3.14
str(100)           # '100'
list("Python")     # ['P', 'y', 't', 'h', 'o', 'n']

Operators

Arithmetic Operators

Operator	Description	Example
+	Addition	10 + 3 → 13
-	Subtraction	10 - 3 → 7
*	Multiplication	10 * 3 → 30
/	Division (float)	10 / 3 → 3.333…
//	Floor Division	10 // 3 → 3
%	Modulus	10 % 3 → 1
**	Exponent	2 ** 3 → 8

a, b = 10, 3
print(a + b)    # 13
print(a // b)   # 3
print(a % b)    # 1
print(a ** b)   # 1000

Comparison Operators

Comparison operators return True or False:

a, b = 10, 3
print(a == b)   # False
print(a != b)   # True
print(a > b)    # True
print(a <= b)   # False

Logical Operators

Operator	Behaviour
and	Returns first falsy value, or last value
or	Returns first truthy value, or last value
not	Reverses the truth value

age = 20
has_id = True

print(age >= 18 and has_id)   # True
print(age < 18 or has_id)     # True
print(not has_id)             # False

Truthy and Falsy Values

Every Python object has a truth value. Falsy values include False, None, 0, 0.0, "", [], (), {}, set(). Everything else is truthy.

print(bool(0))       # False
print(bool(""))      # False
print(bool([]))      # False

print(bool(10))      # True
print(bool("Hi"))    # True
print(bool([1, 2]))  # True

Because and and or return operands rather than booleans, you can use them for concise default values:

name = "" or "Guest"
print(name)   # Guest

Assignment Operators

x = 10
x += 5     # 15
x -= 3     # 12
x *= 2     # 24
x /= 4     # 6.0
x %= 4     # 2.0
x **= 3    # 8.0

Identity and Membership Operators

a = []
b = []
print(a == b)       # True  (same value)
print(a is b)       # False (different objects)

print("a" in "apple")       # True
print(3 in [1, 2, 3])       # True
print("Java" not in "Python")  # True

Bitwise Operators

Bitwise operators work on the binary representation of integers:

Operator	Description	Example
&	AND	5 & 3 → 1
|	OR	5 | 3 → 7
^	XOR	5 ^ 3 → 6
~	NOT	~5 → -6
<<	Left Shift	5 << 1 → 10
>>	Right Shift	5 >> 1 → 2

a, b = 5, 3          # 0101 and 0011 in binary
print(a & b)   # 1
print(a | b)   # 7
print(a ^ b)   # 6
print(a << 1)  # 10
print(a >> 1)  # 2

Control Flow

if / elif / else

marks = 82

if marks >= 90:
    print("A")
elif marks >= 75:
    print("B")
else:
    print("C")
# Output: B

match…case (Python 3.10+)

Python’s structural pattern matching is a powerful alternative to long elif chains:

day = 2

match day:
    case 1:
        print("Monday")
    case 2:
        print("Tuesday")
    case _:
        print("Invalid Day")
# Output: Tuesday

for Loop

for i in range(5):
    print(i)           # 0 1 2 3 4

for name in ["Alice", "Bob"]:
    print(name)

while Loop

count = 1
while count <= 5:
    print(count)
    count += 1

break, continue, and pass

# break — exit the loop immediately
for i in range(10):
    if i == 5:
        break
    print(i)   # 0 1 2 3 4

# continue — skip the current iteration
for i in range(5):
    if i == 2:
        continue
    print(i)   # 0 1 3 4

# pass — placeholder when no action is needed
if True:
    pass

for…else and while…else

The else block runs only when the loop completes without hitting a break:

for i in range(5):
    print(i)
else:
    print("Loop completed")   # Always prints here

Python Nuances

Key things every beginner should know

• Everything in Python is an object — including functions and classes.
• Variables store references, not values directly.
• Use == for value comparison; use is only for identity checks (e.g., x is None).
• Small integers (-5 to 256) are cached by CPython.
• Floating-point arithmetic is not always exact — use math.isclose() for comparisons.
• Indentation defines code blocks — use 4 spaces consistently.
• Lists are mutable; tuples are immutable.
• and and or return operands, not only True/False.
• Truthy/falsy values let you write concise conditionals.