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🐍 Python Syntax Basics

Introduction​

This tutorial covers the essential Python syntax and programming concepts you need to get started. We'll explore variables, data types, control structures, functions, and more. By the end, you'll have a solid foundation to write your first Python programs.

1. Your First Python Program​

Hello World​

# This is a comment
print("Hello, World!")

Running Python Code​

# Save as hello.py and run
python3 hello.py

# Or run interactively
python3
>>> print("Hello, World!")
>>> exit()

2. Variables and Data Types​

Variables​

# Variables don't need type declarations
name = "Alice"
age = 25
height = 5.6
is_student = True

# Print variables
print(name)
print(f"My name is {name} and I'm {age} years old")

Basic Data Types​

# Numbers
integer_number = 42
float_number = 3.14
complex_number = 3 + 4j

# Strings
single_quote = 'Hello'
double_quote = "World"
triple_quote = """This is a
multi-line string"""

# Boolean
is_true = True
is_false = False

# None (represents absence of value)
empty_value = None

# Check data types
print(type(integer_number))  # <class 'int'>
print(type(float_number))    # <class 'float'>
print(type(single_quote))    # <class 'str'>
print(type(is_true))         # <class 'bool'>

3. Numbers and Math Operations​

Arithmetic Operations​

# Basic arithmetic
a = 10
b = 3

print(a + b)    # Addition: 13
print(a - b)    # Subtraction: 7
print(a * b)    # Multiplication: 30
print(a / b)    # Division: 3.333...
print(a // b)   # Floor division: 3
print(a % b)    # Modulo (remainder): 1
print(a ** b)   # Exponentiation: 1000

# Order of operations (PEMDAS)
result = 2 + 3 * 4  # 14, not 20
print(result)

# Parentheses for grouping
result = (2 + 3) * 4  # 20
print(result)

Math Functions​

import math

# Built-in functions
print(abs(-5))           # Absolute value: 5
print(round(3.7))        # Round: 4
print(max(1, 5, 3))      # Maximum: 5
print(min(1, 5, 3))      # Minimum: 1
print(sum([1, 2, 3, 4])) # Sum: 10

# Math module functions
print(math.sqrt(16))     # Square root: 4.0
print(math.pi)           # Pi: 3.14159...
print(math.ceil(4.2))    # Ceiling: 5
print(math.floor(4.8))   # Floor: 4

4. Strings​

String Operations​

# String concatenation
first_name = "John"
last_name = "Doe"
full_name = first_name + " " + last_name
print(full_name)  # John Doe

# String repetition
stars = "*" * 10
print(stars)  # **********

# String length
message = "Hello, Python!"
print(len(message))  # 14

# String indexing
text = "Python"
print(text[0])    # P (first character)
print(text[-1])   # n (last character)
print(text[2:5])  # tho (slice from index 2 to 4)

String Methods​

text = "  Hello, World!  "

# Case methods
print(text.upper())        # "  HELLO, WORLD!  "
print(text.lower())        # "  hello, world!  "
print(text.title())        # "  Hello, World!  "
print(text.capitalize())   # "  hello, world!  "

# Whitespace methods
print(text.strip())        # "Hello, World!"
print(text.lstrip())       # "Hello, World!  "
print(text.rstrip())       # "  Hello, World!"

# Search methods
print(text.find("World"))  # 9
print(text.count("l"))     # 3
print("Hello" in text)     # True

# Replace
print(text.replace("World", "Python"))  # "  Hello, Python!  "

# Split and join
words = "apple,banana,cherry".split(",")
print(words)  # ['apple', 'banana', 'cherry']

joined = "-".join(words)
print(joined)  # apple-banana-cherry

String Formatting​

name = "Alice"
age = 30
score = 95.5

# Old style (%)
print("Name: %s, Age: %d, Score: %.1f" % (name, age, score))

# .format() method
print("Name: {}, Age: {}, Score: {:.1f}".format(name, age, score))
print("Name: {0}, Age: {1}, Score: {2:.1f}".format(name, age, score))
print("Name: {n}, Age: {a}, Score: {s:.1f}".format(n=name, a=age, s=score))

# f-strings (Python 3.6+, recommended)
print(f"Name: {name}, Age: {age}, Score: {score:.1f}")
print(f"Next year I'll be {age + 1} years old")

5. Lists​

Creating and Accessing Lists​

# Create lists
fruits = ["apple", "banana", "cherry"]
numbers = [1, 2, 3, 4, 5]
mixed = [1, "hello", 3.14, True]

# Access elements
print(fruits[0])      # apple
print(fruits[-1])     # cherry
print(fruits[1:3])    # ['banana', 'cherry']

# List length
print(len(fruits))    # 3

List Operations​

fruits = ["apple", "banana"]

# Add elements
fruits.append("cherry")        # Add to end
fruits.insert(1, "orange")     # Insert at index 1
fruits.extend(["grape", "kiwi"])  # Add multiple elements

print(fruits)  # ['apple', 'orange', 'banana', 'cherry', 'grape', 'kiwi']

# Remove elements
fruits.remove("banana")        # Remove by value
popped = fruits.pop()          # Remove and return last element
del fruits[0]                  # Remove by index

# Other operations
print(fruits.count("apple"))   # Count occurrences
print(fruits.index("cherry"))  # Find index
fruits.sort()                  # Sort in place
fruits.reverse()               # Reverse in place

List Comprehensions​

# Traditional way
squares = []
for i in range(5):
    squares.append(i ** 2)
print(squares)  # [0, 1, 4, 9, 16]

# List comprehension (more Pythonic)
squares = [i ** 2 for i in range(5)]
print(squares)  # [0, 1, 4, 9, 16]

# With conditions
even_squares = [i ** 2 for i in range(10) if i % 2 == 0]
print(even_squares)  # [0, 4, 16, 36, 64]

6. Dictionaries​

Creating and Accessing Dictionaries​

# Create dictionary
person = {
    "name": "Alice",
    "age": 30,
    "city": "New York",
    "is_student": False
}

# Access values
print(person["name"])        # Alice
print(person.get("age"))     # 30
print(person.get("salary", "Not specified"))  # Not specified

# Check if key exists
print("name" in person)      # True
print("salary" in person)    # False

Dictionary Operations​

person = {"name": "Alice", "age": 30}

# Add/update values
person["city"] = "New York"
person["age"] = 31

# Remove items
del person["city"]
age = person.pop("age", 0)  # Remove and return value

# Dictionary methods
print(person.keys())         # dict_keys(['name'])
print(person.values())       # dict_values(['Alice'])
print(person.items())        # dict_items([('name', 'Alice')])

# Loop through dictionary
for key, value in person.items():
    print(f"{key}: {value}")

7. Control Structures​

Conditional Statements (if/elif/else)​

age = 18

if age < 13:
    print("Child")
elif age < 20:
    print("Teenager")
elif age < 65:
    print("Adult")
else:
    print("Senior")

# Multiple conditions
score = 85
if score >= 90 and score <= 100:
    grade = "A"
elif score >= 80 and score < 90:
    grade = "B"
else:
    grade = "C"

print(f"Grade: {grade}")

# Ternary operator
status = "adult" if age >= 18 else "minor"
print(status)

Loops​

For Loops​

# Loop through a list
fruits = ["apple", "banana", "cherry"]
for fruit in fruits:
    print(fruit)

# Loop with index
for i, fruit in enumerate(fruits):
    print(f"{i}: {fruit}")

# Loop through a range
for i in range(5):
    print(i)  # 0, 1, 2, 3, 4

for i in range(2, 8, 2):
    print(i)  # 2, 4, 6

# Loop through dictionary
person = {"name": "Alice", "age": 30, "city": "NYC"}
for key, value in person.items():
    print(f"{key}: {value}")

While Loops​

# Basic while loop
count = 0
while count < 5:
    print(f"Count: {count}")
    count += 1

# Break and continue
count = 0
while count < 10:
    count += 1
    if count == 3:
        continue  # Skip the rest of this iteration
    if count == 7:
        break     # Exit the loop
    print(count)  # 1, 2, 4, 5, 6

8. Functions​

Defining and Calling Functions​

# Simple function
def greet():
    print("Hello, World!")

greet()  # Call the function

# Function with parameters
def greet_person(name, age=25):
    print(f"Hello, {name}! You are {age} years old.")

greet_person("Alice")           # Hello, Alice! You are 25 years old.
greet_person("Bob", 30)         # Hello, Bob! You are 30 years old.

# Function with return value
def add_numbers(a, b):
    return a + b

result = add_numbers(5, 3)
print(result)  # 8

# Multiple return values
def get_name_parts(full_name):
    parts = full_name.split()
    return parts[0], parts[-1]  # Returns tuple

first, last = get_name_parts("John Doe")
print(f"First: {first}, Last: {last}")

Function Examples​

# Calculate area of rectangle
def rectangle_area(length, width):
    """Calculate the area of a rectangle."""
    return length * width

area = rectangle_area(5, 3)
print(f"Area: {area}")

# Check if number is even
def is_even(number):
    return number % 2 == 0

print(is_even(4))   # True
print(is_even(7))   # False

# Find maximum in a list
def find_max(numbers):
    if not numbers:
        return None
    max_num = numbers[0]
    for num in numbers[1:]:
        if num > max_num:
            max_num = num
    return max_num

numbers = [3, 7, 2, 9, 1]
print(f"Maximum: {find_max(numbers)}")

9. Error Handling​

Try/Except Blocks​

# Basic error handling
try:
    number = int(input("Enter a number: "))
    result = 10 / number
    print(f"Result: {result}")
except ValueError:
    print("Please enter a valid number!")
except ZeroDivisionError:
    print("Cannot divide by zero!")
except Exception as e:
    print(f"An error occurred: {e}")
else:
    print("No errors occurred!")
finally:
    print("This always runs!")

# Multiple exceptions
try:
    # Some code that might fail
    pass
except (ValueError, TypeError) as e:
    print(f"Input error: {e}")
except Exception as e:
    print(f"Unexpected error: {e}")

10. File Operations​

Reading and Writing Files​

# Write to file
with open("example.txt", "w") as file:
    file.write("Hello, World!\n")
    file.write("This is a test file.\n")

# Read from file
with open("example.txt", "r") as file:
    content = file.read()
    print(content)

# Read line by line
with open("example.txt", "r") as file:
    for line in file:
        print(line.strip())  # strip() removes newline characters

# Append to file
with open("example.txt", "a") as file:
    file.write("This line was appended.\n")

11. Modules and Imports​

Using Built-in Modules​

# Import entire module
import math
print(math.pi)
print(math.sqrt(16))

# Import specific functions
from math import pi, sqrt
print(pi)
print(sqrt(16))

# Import with alias
import datetime as dt
now = dt.datetime.now()
print(now)

# Import all (not recommended)
from math import *
print(sin(pi/2))  # 1.0

Creating Your Own Module​

# Save as calculator.py
def add(a, b):
    return a + b

def multiply(a, b):
    return a * b

# Use in another file
from calculator import add, multiply
print(add(5, 3))        # 8
print(multiply(4, 6))   # 24

12. Practice Exercises​

Exercise 1: Temperature Converter​

def celsius_to_fahrenheit(celsius):
    """Convert Celsius to Fahrenheit."""
    return (celsius * 9/5) + 32

def fahrenheit_to_celsius(fahrenheit):
    """Convert Fahrenheit to Celsius."""
    return (fahrenheit - 32) * 5/9

# Test the functions
c = 25
f = celsius_to_fahrenheit(c)
print(f"{c}°C = {f}°F")

f = 77
c = fahrenheit_to_celsius(f)
print(f"{f}°F = {c}°C")

Exercise 2: Word Counter​

def count_words(text):
    """Count words in a text."""
    words = text.split()
    return len(words)

def count_characters(text):
    """Count characters (excluding spaces)."""
    return len(text.replace(" ", ""))

# Test
text = "Hello world! This is a test."
print(f"Words: {count_words(text)}")
print(f"Characters: {count_characters(text)}")

Exercise 3: Number Guessing Game​

import random

def guessing_game():
    """Simple number guessing game."""
    secret_number = random.randint(1, 100)
    attempts = 0
    
    print("I'm thinking of a number between 1 and 100.")
    
    while True:
        try:
            guess = int(input("Enter your guess: "))
            attempts += 1
            
            if guess < secret_number:
                print("Too low!")
            elif guess > secret_number:
                print("Too high!")
            else:
                print(f"Congratulations! You guessed it in {attempts} attempts!")
                break
        except ValueError:
            print("Please enter a valid number!")

# Uncomment to play
# guessing_game()

Conclusion​

You've learned the fundamental Python syntax including:

  • Variables and data types (int, float, str, bool, list, dict)
  • Control structures (if/elif/else, for/while loops)
  • Functions (defining, calling, parameters, return values)
  • Error handling (try/except blocks)
  • File operations (reading and writing files)
  • Modules (importing and using)

Next Steps​