Introduction to Python

What Is Python?

Python is a high-level, interpreted, general-purpose programming language created by Guido van Rossum and first released in 1991. The name comes from Monty Python’s Flying Circus — Guido wanted something fun to work with. Python prioritizes developer productivity: its readable syntax reduces the cognitive overhead of writing code, so you can focus on solving problems rather than fighting the language.

Its design philosophy, captured in The Zen of Python (import this), prioritizes readability and simplicity:

“There should be one — and preferably only one — obvious way to do it.”

A Quick History

Understanding Python’s history helps explain why you might encounter both python and python3 commands, or why some older tutorials use outdated syntax. The Python 2 to Python 3 transition was a deliberate breaking change to fix deep design mistakes — everything you learn today targets Python 3.

Where Python Is Used

Python’s versatility is one of its biggest strengths. Unlike languages that dominate a single domain, Python is productively used across web development, machine learning, automation, and scientific computing — often by the same team.

Web Development

Frameworks like Django and FastAPI power companies like Instagram, Dropbox, and thousands of startups. FastAPI in particular is used when you need high-performance async REST or GraphQL APIs — it generates OpenAPI documentation automatically and uses Python type hints for request validation.

# A complete REST endpoint in FastAPI — under 10 lines
from fastapi import FastAPI

app = FastAPI()

@app.get("/users/{user_id}")
async def get_user(user_id: int):
    # FastAPI validates that user_id is an int automatically
    return {"user_id": user_id, "name": "Alice"}

Data Science and Machine Learning

NumPy, Pandas, scikit-learn, PyTorch, and TensorFlow have made Python the default language for data work. The ecosystem is so mature that switching to another language for ML would mean rebuilding years of tooling from scratch.

import pandas as pd

# Load a CSV, group by product, sum revenue, return top 10
df = pd.read_csv("sales.csv")
top_products = (
    df.groupby("product")["revenue"]
    .sum()
    .sort_values(ascending=False)
    .head(10)
)

Automation and Scripting

Python replaced Bash for complex automation tasks because it handles errors, data structures, and APIs far more cleanly. You can scrape websites, orchestrate cloud infrastructure (Ansible, Pulumi), or write CI/CD tooling in a fraction of the time it would take in other languages.

import pathlib
import shutil
import time

# Archive all log files older than 7 days — readable without comments
logs = pathlib.Path("/var/log/app")
for log in logs.glob("*.log"):
    if log.stat().st_mtime < (time.time() - 7 * 86400):
        shutil.move(str(log), "/archive/logs/")

System Administration and DevOps

Tools like Ansible, SaltStack, and AWS CDK are written in Python. Most cloud provider CLIs (AWS, GCP, Azure) are Python-based and expose rich Python SDKs, making Python the natural choice for infrastructure automation.

Finance and Quant

Bloomberg, JPMorgan, and most hedge funds use Python for modeling, backtesting, and risk analysis. The zipline, QuantLib, and pandas-datareader ecosystems are mature and battle-tested in production trading systems.

Python vs. Other Languages

Python’s main trade-off is raw execution speed for developer speed. For the vast majority of real-world tasks — web APIs, data pipelines, automation — the bottleneck is I/O or an external service, not CPU, so Python’s interpreted overhead never shows up.

Career Opportunities

Python consistently ranks #1 or #2 on the TIOBE Index and Stack Overflow surveys. Strong Python skills open doors across multiple well-compensated engineering tracks, and the demand continues to grow as ML and automation become standard parts of every engineering organization.

• Data Engineer — build pipelines with Airflow, Spark, dbt
• ML Engineer — train, optimize, and serve models at scale
• Backend Developer — APIs, microservices, background workers
• DevOps/Platform Engineer — infrastructure automation, Kubernetes operators
• Security Engineer — penetration testing, exploit development (Metasploit has Python bindings)

Your First Python Program

A Python script is just a text file ending in .py. The if __name__ == "__main__": guard is a standard pattern that separates reusable module code from executable script code — it only runs when the file is invoked directly, not when it’s imported by another module.

# hello.py
def greet(name: str) -> str:
    # Type hints document what the function expects and returns
    return f"Hello, {name}! Welcome to Python."

if __name__ == "__main__":
    # This block is skipped when the file is imported as a module
    print(greet("World"))

Run it with:

python hello.py
# Hello, World! Welcome to Python.

What’s Next

The next tutorial covers installing Python, setting up a virtual environment, and configuring VS Code — the practical foundation before writing real code.