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Manuals / Python / Ch 5

B · StructureIntermediate40 min read

5. Files, JSON & pathlib

Python · 52 pages source format

with open(...) for files. json.load/dump. pathlib.Path for cross-platform paths. Test data lives in JSON.

What you'll learn

  • with open context manager
  • json module
  • pathlib.Path
  • Reading test fixtures

Read and write files

with open(path) as f: always closes the file. Specify encoding="utf-8" on Windows.

import json

with open("users.json", encoding="utf-8") as f:
    users = json.load(f)

for u in users:
    print(u["username"])

Do this now

Write users.json with 3 users. Load in Python and print usernames.

Clear?

pathlib

Path("data/users.json") / "subdir" — cleaner than os.path.join.

Do this now

Refactor file paths to use pathlib.Path.

Clear?

Write JSON output

json.dump(data, f, indent=2) for readable output files from glue scripts.

Do this now

Script: read CSV or JSON → transform → write summary.json.

Clear?

Checklist