What Python is, and running your first program

Python is a language for giving a computer step-by-step instructions in words that read almost like English. This page gets one running.

A Python program is a text file ending in .py. Python reads it from the top line to the bottom, one instruction at a time. Data engineers use it to read files, clean data, call APIs and load warehouses, because the code stays short and the libraries already exist for almost every job.

Step 1: set up once

# 1. Check Python is installed (3.10 or newer)
python3 --version

# 2. Make a folder and a virtual environment for it
mkdir python_de && cd python_de
python3 -m venv .venv
source .venv/bin/activate
# on Windows: .venv\Scripts\activate

# 3. Save the code on the right as hello.py, then run it
python3 hello.py

No Python yet? Install it from python.org (tick "Add Python to PATH" on Windows). Use VS Code as your editor, or Jupyter if you like running code in small pieces.

Step 2: your first program

# Lines starting with # are comments.
# Python ignores them; they are notes for humans.

print("Hello, data engineer!")
print("Orders today:", 15)
print(2 + 3)

Hello, data engineer!
Orders today: 15
5

Three rules Python is strict about

amount = 1198
if amount > 1000:
    print("big order")  # 4 spaces: inside the if
print("done")          # back left: after the if

big order
done

print("Amount")
Print("Amount")        # capital P: another name

Amount
NameError: name 'Print' is not defined. Did you mean: 'print'?