Python Basics: How to Install Python and Write Your First Script (2026 Guide)

Python is the most-used programming language in AI, data science, and automation. It's also widely considered the easiest language to learn first — the syntax is close to plain English and the feedback loop is immediate.

This guide gets you from nothing to a working Python setup with a real script in under 30 minutes.

Step 1: Install Python

macOS

Check if Python is already installed:

python3 --version

If you see Python 3.10 or higher, you can skip to Step 2. If not, or if you want the latest version:

Option A — Homebrew (recommended):

brew install python

If you don't have Homebrew, install it first:

/bin/bash -c "$(curl -fsSL https://raw.githubusercontent.com/Homebrew/install/HEAD/install.sh)"

Option B — Official installer:

1. Go to python.org/downloads
2. Download the latest Python 3.13.x macOS installer
3. Run the .pkg file and follow the installer

After installation:

python3 --version

You should see Python 3.13.x.

Windows

1. Go to python.org/downloads
2. Download Python 3.13.x (Windows installer)
3. Run the installer
4. Important: Check the box that says "Add Python to PATH" before clicking Install

Open Command Prompt or PowerShell and verify:

python --version

On Windows, the command is python (not python3). On Mac/Linux, use python3 to avoid accidentally using an old Python 2 installation.

Step 2: Install a code editor

If you haven't already, install Cursor or VS Code. Both have excellent Python support.

In VS Code or Cursor, install the Python extension by Microsoft — it adds syntax highlighting, autocomplete, and the ability to run Python files directly in the editor.

Step 3: Write and run your first script

Create a folder for your Python projects:

mkdir python-projects
cd python-projects

Create your first Python file:

# Mac/Linux
touch hello.py

# Windows
type nul > hello.py

Open hello.py in your editor and type:

print("Hello, Python!")

name = "Alice"
print(f"Hello, {name}!")

numbers = [1, 2, 3, 4, 5]
total = sum(numbers)
print(f"The sum of {numbers} is {total}")

Run it:

# Mac/Linux
python3 hello.py

# Windows
python hello.py

Output:

Hello, Python!
Hello, Alice!
The sum of [1, 2, 3, 4, 5] is 15

The core concepts

Variables

Variables store values. No type declaration needed — Python figures it out:

name = "Alice"           # string
age = 28                 # integer
height = 5.7             # float
is_student = True        # boolean

print(name, age, height, is_student)

Strings and f-strings

first = "Alice"
last = "Smith"

# Concatenation (old way)
full = first + " " + last

# f-strings (modern way — preferred)
full = f"{first} {last}"
greeting = f"Hello, {first}! You are {age} years old."

print(greeting)

Lists

fruits = ["apple", "banana", "cherry"]

print(fruits[0])         # apple — indexing starts at 0
print(fruits[-1])        # cherry — last item

fruits.append("mango")   # add to end
fruits.remove("banana")  # remove by value

print(len(fruits))       # 3 — number of items

Dictionaries

person = {
    "name": "Alice",
    "age": 28,
    "city": "London"
}

print(person["name"])    # Alice
person["job"] = "Engineer"  # add a new key
print(person)

If / else

age = 20

if age >= 18:
    print("You are an adult")
elif age >= 13:
    print("You are a teenager")
else:
    print("You are a child")

For loops

fruits = ["apple", "banana", "cherry"]

for fruit in fruits:
    print(f"I like {fruit}")

# Loop over a range of numbers
for i in range(5):
    print(i)   # prints 0, 1, 2, 3, 4

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

Functions

def greet(name):
    return f"Hello, {name}!"

def add(a, b):
    return a + b

message = greet("Alice")
print(message)

result = add(3, 4)
print(result)    # 7

Functions with default parameters:

def greet(name, greeting="Hello"):
    return f"{greeting}, {name}!"

print(greet("Alice"))           # Hello, Alice!
print(greet("Bob", "Hi"))       # Hi, Bob!

Step 4: Set up a virtual environment

A virtual environment isolates your project's packages from the rest of your system. Always use one.

Create a virtual environment in your project folder:

# Mac/Linux
python3 -m venv venv

# Windows
python -m venv venv

Activate it:

# Mac/Linux
source venv/bin/activate

# Windows (Command Prompt)
venv\Scripts\activate.bat

# Windows (PowerShell)
venv\Scripts\Activate.ps1

When activated, your terminal prompt shows (venv) at the start:

(venv) user@machine:~/python-projects$

Everything you install now goes into this environment, not your system Python.

To deactivate when you're done:

deactivate

Step 5: Install packages with pip

pip is Python's package installer. With your virtual environment active:

pip install requests

This installs the requests library — the standard way to make HTTP calls in Python.

Test it:

import requests

response = requests.get("https://api.github.com")
print(response.status_code)   # 200
print(response.json()["current_user_url"])

Save your dependencies so others can replicate your environment:

pip freeze > requirements.txt

To install from a requirements.txt on a new machine:

pip install -r requirements.txt

Step 6: A real beginner project

Build a script that fetches today's weather for any city using a free API.

Install the requests library if you haven't:

pip install requests

Create weather.py:

import requests

def get_weather(city):
    url = f"https://wttr.in/{city}?format=j1"
    response = requests.get(url)
    
    if response.status_code != 200:
        return f"Could not fetch weather for {city}"
    
    data = response.json()
    current = data["current_condition"][0]
    
    temp_c = current["temp_C"]
    feels_like = current["FeelsLikeC"]
    description = current["weatherDesc"][0]["value"]
    
    return f"{city}: {description}, {temp_c}°C (feels like {feels_like}°C)"

cities = ["London", "New York", "Tokyo", "Mumbai"]

for city in cities:
    print(get_weather(city))

Run it:

python3 weather.py

You're fetching live data, parsing JSON, and printing formatted output — with less than 25 lines of code.

Common beginner mistakes

Not activating the virtual environment. If you install packages and they "don't work", check that (venv) is showing in your terminal prompt.

Using python vs python3. On Mac/Linux, always use python3. On Windows, python usually points to Python 3 if you installed it correctly.

Indentation errors. Python uses indentation (spaces) instead of curly braces to structure code. Mixing tabs and spaces causes errors. Use spaces consistently (4 spaces per indent is the standard).

Forgetting to save the file. Python runs whatever is on disk, not what's in your editor. Save before running.

What to learn next

• File I/O — reading and writing files with open()
• Error handling — try / except blocks
• List comprehensions — [x * 2 for x in numbers] — a concise way to build lists
• Classes — object-oriented programming with class
• Common libraries — pandas for data, flask for web APIs, anthropic for Claude AI

The Anthropic Python SDK lets you call Claude from a Python script:

pip install anthropic

import anthropic

client = anthropic.Anthropic()

message = client.messages.create(
    model="claude-sonnet-4-6",
    max_tokens=1024,
    messages=[{"role": "user", "content": "Explain Python decorators simply."}]
)

print(message.content[0].text)

Python is the language most AI and ML work is written in — now you have the foundation to explore it.