This is the Day 1 companion exercise for the AI Path L1→L2 Upgrade Guide. Read Part 1 first, then come back here to practice.

Today we do exactly one thing: run the hello_api.py from Part 1 and see AI reply in your terminal.

Prerequisites

Complete these steps from Part 1 (skip if already done):

  • Register a DeepSeek developer account (Part 1, “Register for API Accounts”)
  • Get your API Key and save it to a .env file (Part 1, “API Key Safety”)
  • Install uv and Python 3.12 (Part 1, “Install Python”)
  • Create a virtual environment and install dependencies (Part 1, “Create a Virtual Environment”)

Confirm your project directory looks like this:

your-project/
├── .env                  # DEEPSEEK_API_KEY=sk-xxx
└── .venv/                # uv-managed virtual environment

Ready? Let’s go.

“Write” Your Code

Create hello_api.py in your project directory and paste this in:

import os
from dotenv import load_dotenv
from openai import OpenAI

# Load .env file
load_dotenv()

# Read API Key
api_key = os.environ.get("DEEPSEEK_API_KEY")
if not api_key:
    raise ValueError("DEEPSEEK_API_KEY not set. Check your .env file.")

# Create client
client = OpenAI(
    api_key=api_key,
    base_url="https://api.deepseek.com"
)

# Send request
response = client.chat.completions.create(
    model="deepseek-v4-flash",
    messages=[
        {"role": "user", "content": "Hello, introduce yourself in one sentence."}
    ]
)

# Print response
print(response.choices[0].message.content)

Run it:

uv run python hello_api.py

AI replied with a sentence? You’re done. Now try this: change the question to anything you want and run it again. For example, "Write a Python number-guessing game" or "Explain what an API is."

Troubleshooting

“DEEPSEEK_API_KEY not set”

  • Is .env in the same directory as hello_api.py? Move it there if not.
  • Is the Key complete? It should start with sk-, no extra spaces.
  • Is the filename exactly .env? Check for leading spaces or hidden extensions.

“Connection refused” or network errors

  • Is your network working? Can you open platform.deepseek.com in a browser?
  • Is base_url correct: https://api.deepseek.com (note: https, no /v1 at the end)?

“Insufficient balance”

  • New accounts get a small free credit. Once it runs out, top up in the console.
  • A few dollars (or 10 RMB) lasts a long time for practice.

“Model not found”

  • Double-check the model name: deepseek-v4-flash. The old name deepseek-chat still works but the new name is recommended.

“Authentication failed” / “Invalid API key”

  • Key might be incomplete or have trailing spaces.
  • Create a new Key in the console and replace the value in .env.

What You Did Today

  • Ran your first API code
  • Saw AI reply in your terminal
  • Changed the question and ran it again

Next up: Day 2 switches to a different platform (an aggregator). Same code, change two parameters, different AI service. You’ll see how portable your skills are.

Stuck on an error? Share the error message and your .env file structure (never the Key itself) in the reader group.