Below is a concise, copy-paste-ready cheat sheet for the most frequently used Python snippets inside n8n.
Each bullet = one mini-recipe.
Drop the code straight into the Code → Python node and run.

1. Read a field from the previous node

return {"newKey": item["json"]["oldKey"]}

2. Add a static constant

return {"status": "paid", "source": "n8n"}

3. UTC timestamp as an ISO string

import datetime
return {"ts": datetime.datetime.utcnow().isoformat()}

4. Trim/slice a string

return {"short": item["json"]["orderId"][-6:]}

5. Remove new-lines or extra spaces

return {"clean": item["json"]["title"].replace("\n", " ")}

6. Normalise case

return {"email": item["json"]["mail"].lower()}

7. Quick if/else tag

amt = item["json"]["amount"]
return {"tag": "VIP" if amt > 1000 else "Normal"}

8. Filter a list in one line

ok = [x for x in item["json"]["lines"] if x["status"] == "ok"]
return {"okLines": ok}

9. Sum values inside an array

total = sum(float(l["price"]) for l in item["json"]["lines"])
return {"total": total}

10. Deduplicate by ID (keep 1st)

seen = set()
uniq = [x for x in item["json"]["list"]
        if x["id"] not in seen and not seen.add(x["id"])]
return {"uniq": uniq}

11. Build a friendly sentence

return {"text": f'{item["json"]["name"]} 的订单 {item["json"]["id"]} 已发货'}

12. Random coupon code (8 chars)

import secrets, string
alphabet = string.ascii_uppercase + string.digits
return {"code": ''.join(secrets.choice(alphabet) for _ in range(8))}

13. Base64 encode for Basic auth

import base64
return {"b64": base64.b64encode(item["json"]["text"].encode()).decode()}

14. JSON → string (pretty log)

import json
return {"str": json.dumps(item["json"], ensure_ascii=False)}

15. String → JSON (parse raw body)

import json
return json.loads(item["json"]["raw"])

16. Fire a quick POST (no HTTP node)

import requests
r = requests.post("https://api.x.com", json=item["json"], timeout=10)
return r.json()

17. Grab an environment variable

import os
return {"token": os.getenv("API_TOKEN")}

18. Single-row CSV export

import csv, io
o = io.StringIO()
w = csv.DictWriter(o, fieldnames=["id", "amount"])
w.writeheader()
w.writerow(item["json"])
return {"csv": o.getvalue()}

19. Rate-limiting pause (0.3 s)

import time
time.sleep(0.3)
return item["json"]

20. Halt workflow on bad data

if not item["json"].get("email"):
    raise ValueError("email missing")

Tips

• Whatever you return become is the new item.json for the next node.
• Need heavy libs (pandas, numpy)? Install them first via Settings → Community nodes or a Execute Command node:

pip install pandas

• For snippets rated complex, consider wrapping them in a sub-workflow and calling them with Execute Workflow—it keeps the main flow tidy.

Happy automating!