Files, JSON & YAML

Beginner ⭐ 50 XP ⏱ 16 min #python#json#yaml#files

Read and write files and structured config formats — the bread and butter of automation.

📖Theory

Most automation reads config and writes results. Python makes this easy:

Files: open with a with block so they close automatically even on error
JSON: the built-in json module ↔ dicts/lists (json.load, json.dumps)
YAML: via pyyaml (yaml.safe_load) — common for Kubernetes/CI config

json.dumps(obj, indent=2) pretty-prints; yaml.safe_load (not load) avoids executing arbitrary tags from untrusted files.

🌍Real-World Example

import json

# Read JSON config, modify, write it back pretty-printed
with open("config.json") as f:
    cfg = json.load(f)

cfg["replicas"] = cfg.get("replicas", 1) + 1

with open("config.json", "w") as f:
    json.dump(cfg, f, indent=2)

# YAML (needs: pip install pyyaml)
import yaml
with open("deploy.yaml") as f:
    spec = yaml.safe_load(f)
print(spec["kind"])

✍️Hands-On Exercise

Read a text file line by line and count non-empty lines.
Load a JSON file, add a key, and write it back with indentation.
Parse a YAML file with yaml.safe_load and print one nested value.
Explain why a with block is preferred over manually calling open/close.

🧾Cheat Sheet▾

Task	Code
Read file	`with open(p) as f: data = f.read()`
Write file	`with open(p, "w") as f: f.write(s)`
Parse JSON	`json.load(f)` / `json.loads(s)`
Dump JSON	`json.dump(o, f, indent=2)`
Parse YAML	`yaml.safe_load(f)`
Append mode	`open(p, "a")`

💬Common Interview Questions▾

Why use a with block to open files?

It’s a context manager that guarantees the file is closed when the block exits, even if an exception occurs — preventing leaked file handles.

Why prefer yaml.safe_load over yaml.load?

safe_load only constructs basic Python types, avoiding arbitrary code/object execution that the full loader allows from untrusted YAML.

📚Official Documentation

↗ Python — Reading and writing files

📝 My notes on this topic

Auto-saves as you type