Python JSON Read and Write Examples (Step-by-Step)

JSON is the most common format for exchanging data on the web. In this beginner-friendly guide, you’ll learn exactly how to read and write JSON in Python using the built-in json module. We will go step by step with simple, runnable code, so you can confidently load data from a file, convert Python dictionaries to JSON, pretty print JSON, and avoid the most common mistakes. If you’re just getting started with Python, you can also browse our other lessons at CodDesire Python tutorials.

Python JSON read and write examples (step-by-step)

Python JSON read example: loading data from a file into dictionaries and lists for beginners — How JSON data loads into Python objects in a beginner-friendly flow.

What you’ll learn

How to read JSON file in Python with json.load()
How to write JSON to file in Python with json.dump()
Read and parse JSON in Python with examples using json.loads()
Python dictionary to JSON example (and save to a file)
Pretty print JSON in Python for beginners
json load and dump explained (including load vs loads, dump vs dumps)

Key takeaways: Python JSON read and write examples

Use json.load/json.dump for files; use json.loads/json.dumps for strings in memory.
Open files with encoding="utf-8"; set ensure_ascii=False to keep Unicode readable.
Pretty output: indent=2, optional sort_keys=True. Compact output: separators=(",", ":").
Custom types: pass default= to dumps/dump (e.g., serialize datetime to ISO).
Accuracy and strictness: use parse_float=Decimal when loading money; allow_nan=False to reject NaN/Infinity.

What is JSON in Python and why is it useful?

Python JSON write example: saving dictionaries and lists to a formatted JSON file — Turning Python objects into a neatly formatted JSON file.

JSON (JavaScript Object Notation) is a text format for structured data. It is language-independent, lightweight, and maps cleanly to Python types. Use JSON whenever you want to store or exchange structured data (e.g., settings, user profiles, quiz results, or API responses).

The Python standard library includes json for encoding (writing) and decoding (reading) JSON. Here is how common types map between Python and JSON:

Python	JSON	Notes
`dict`	object	String keys; key order is not semantically meaningful
`list`, `tuple`	array	Tuples become arrays
`str`	string	JSON strings use double quotes
`int`, `float`	number	Prefer valid JSON numbers (avoid NaN/Infinity for portability)
`True`, `False`, `None`	`true`, `false`, `null`	Automatic conversion

Quick start: write then read a JSON file

Simple example: write JSON file in Python

This is the simplest way to save a Python dictionary as JSON using json.dump(). We also format the output for readability.

import json

student = {
"id": 101,
"name": "Anita",
"active": True,
"scores": [85, 91, 78]
}

# Write JSON to a file (UTF-8). ensure_ascii=False lets Unicode characters be written directly.
with open("student.json", "w", encoding="utf-8") as f:
json.dump(student, f, ensure_ascii=False, indent=2, sort_keys=True)

print("Wrote student.json")

Read and parse JSON in Python with examples

Now load the same file back into Python using json.load() and compute something simple.

import json

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

avg = sum(data["scores"]) / len(data["scores"])
print(data["name"], f"avg={avg:.2f}")

Output

Anita avg=84.67

How to read JSON strings vs files

Use json.load() for files, and json.loads() for JSON text in a Python string (e.g., from an API response).

How data flows when you write and read JSON

Write JSON

Python dict/list

→

json.dumps()

json.dump()

→

JSON text / .json file

Tip: indent, ensure_ascii, sort_keys control formatting.

Read JSON

JSON string/file

→

json.loads()

json.load()

→

Python dict/list

Options: parse_float=Decimal, object_hook=..., strict behavior.

Read JSON from a string with json.loads()

import json

json_text = '{"id": 1, "tags": ["json", "python"], "done": false}'
obj = json.loads(json_text)

print(obj["tags"][0]) # Access data like a normal Python dict

Output

json

Step by step: python json load from file

Import the module: import json
Open the file with UTF-8 encoding
Call json.load(file_object) to parse JSON into Python types
Use the data (index lists, read keys, loop, etc.)

import json

# 1-2) Open file
with open("student.json", encoding="utf-8") as f:
# 3) Parse JSON
student = json.load(f)

# 4) Use data
for i, score in enumerate(student["scores"], start=1):
print(f"Test {i}: {score}")

Output

Test 1: 85
Test 2: 91
Test 3: 78

How to write JSON: dump vs dumps (with pretty print)

Use json.dump(obj, file) to write directly to a file; use json.dumps(obj) to get a JSON string (for printing, logging, or sending over a network).

Python dictionary to JSON example (file + string)

Code

class="cd-package">import json

profile = {"username": "coder", "level": 5, "skills": ["python", "json"]}

# Write to a file
with open("profile.json", "w", encoding="utf-8") as f:
    json.dump(profile, f, ensure_ascii=False, indent=2)

# Get a pretty JSON string
pretty = json.dumps(profile, ensure_ascii=False, indent=2, sort_keys=True)
print(pretty)

Output

{
  "level": 5,
  "skills": [
    "python",
    "json"
  ],
  "username": "coder"
}

Compact vs pretty output

indent=2 makes it readable for humans.
separators=(',', ':') removes spaces for compact output (smaller files).
ensure_ascii=False writes Unicode directly (the default is True, which escapes non-ASCII characters).

Pretty vs compact JSON: trade‑offs (illustrative)

Pretty (indent=2)

Human readability

Compactness

Compact (separators=(“,”, “:”))

Human readability

Compactness

Use pretty for learning/debugging; use compact for network transfer or storage.

import json

obj = {"greet": "नमस्ते", "count": 3}

pretty = json.dumps(obj, ensure_ascii=False, indent=2)
compact = json.dumps(obj, ensure_ascii=False, separators=(",", ":"))

print("Pretty:")
print(pretty)
print("Compact:")
print(compact)

Output

Pretty:
{
  "count": 3,
  "greet": "नमस्ते"
}
Compact:
{"greet":"नमस्ते","count":3}

json.load vs json.loads and json.dump vs json.dumps

These pairs behave the same way, except one works with files and the other with strings. Here is the quick reference:

API	Works with	Input	Returns	Typical use
`json.load(fp)`	File object	Open file containing JSON text (UTF-8 recommended)	Python object	Read from a .json file
`json.loads(s)`	String or bytes	JSON text in memory	Python object	Parse API response or a string
`json.dump(obj, fp)`	File object	Python object	None (writes to file)	Save to a .json file
`json.dumps(obj)`	String	Python object	JSON string	Print, log, or send over network

Full example: python convert dictionary to JSON and save to file, then read it back

import json
from pathlib import Path

students = [
{"id": 1, "name": "Asha", "scores": [88, 92]},
{"id": 2, "name": "Ravi", "scores": [75, 81]},
]

# Save as pretty JSON
path = Path("students.json")
path.write_text(json.dumps(students, ensure_ascii=False, indent=2), encoding="utf-8")

# Read back and compute the average of the first student
loaded = json.loads(path.read_text(encoding="utf-8"))
avg = sum(loaded[0]["scores"]) / len(loaded[0]["scores"])
print(loaded[0]["name"], f"avg={avg:.1f}")

Output

Asha avg=90.0

Common mistakes and how to fix them

Using single quotes or trailing commas in JSON text. JSON requires double quotes for keys and strings, and no trailing commas.
Forgetting file encoding. Always open files with encoding="utf-8" for portability.
Assuming JSON keeps object key order. JSON object key order has no semantic meaning. Use sort_keys=True only when you need deterministic output (e.g., tests).
Expecting datetime, set, or Decimal to serialize automatically. The json module doesn’t handle these by default. Convert or use default=.
Relying on NaN/Infinity. They are outside the JSON spec and may break other parsers. You can enforce strictness with allow_nan=False.
Forgetting to close files. Use with open(...) so files close automatically.

Serialize custom types (e.g., datetime) with default=

Code

class="cd-package">import json
from datetime class="cd-package">import datetime

record = {"event": "login", "at": datetime(2025, 1, 2, 14, 30)}

# Convert unknown objects to strings(ISO 8601 here)
js = json.dumps(record, default=lambda o: o.isoformat(), ensure_ascii=False, indent=2)
print(js)

Preserve numeric precision when reading floats

If you need exact decimal math (e.g., currency), use parse_float=Decimal while loading.

import json
from decimal import Decimal

text = '{"price": 12.34, "qty": 2}'
data = json.loads(text, parse_float=Decimal)

total = data["price"] * data["qty"]
print(type(data["price"]), total)

Output

<class 'decimal.Decimal'> 24.68

Disallow NaN/Infinity for strict JSON

import json
import math

bad = {"value": math.nan}
try:
json.dumps(bad, allow_nan=False)
except ValueError as e:
print("Error:", e)

Output

Error: Out of range float values are not JSON compliant

Bonus: JSON Lines (one JSON value per line)

For logs and streaming, write one JSON object per line (also called NDJSON/JSON Lines). This still uses the standard library.

import json

records = [{"id": 1, "name": "A"}, {"id": 2, "name": "B"}]

# Write JSON Lines
with open("people.jsonl", "w", encoding="utf-8") as f:
for r in records:
f.write(json.dumps(r, ensure_ascii=False) + "n")

# Read JSON Lines
people = []
with open("people.jsonl", encoding="utf-8") as f:
for line in f:
people.append(json.loads(line))

print(len(people), people[0]["name"])

Output

2 A

FAQ: python json tutorial for beginners

What is JSON in Python and why is it useful?

JSON is a text format for structured data. In Python, the built-in json module lets you convert between JSON and Python types like dict, list, str, numbers, and booleans. It’s useful because it’s simple, human-readable, and widely used by web APIs, configuration files, and data exchange. JSON does not allow comments.

How do I read a JSON file using json.load() in Python?

import json
with open("data.json", encoding="utf-8") as f:
data = json.load(f)
print(type(data))

How do I write a Python dictionary to a JSON file with json.dump()?

import json
data = {"course": "Python", "completed": False}
with open("course.json", "w", encoding="utf-8") as f:
json.dump(data, f, ensure_ascii=False, indent=2)

What is the difference between json.load vs json.loads and json.dump vs json.dumps?

load/dump work with file objects; loads/dumps work with strings (in memory). Functionality is otherwise the same.

How can I pretty print or format JSON output in Python?

Use json.dumps(obj, indent=2, sort_keys=True) to get a nicely formatted string, or json.dump(obj, f, indent=2) to write formatted JSON to a file.

Tips and extras

Command line helper (Python 3.14+): you can quickly format or validate JSON files using python -m json with options like --indent 2 or --sort-keys.
Pathlib shortcuts: Path("file.json").read_text(encoding="utf-8") and write_text(...) work well with json.loads()/json.dumps().
Keep learning: explore file handling, error handling (try/except json.JSONDecodeError), and APIs to fetch JSON over HTTP.

Sources / Further reading

That’s it! With these python json read and write examples, you can load files, generate clean JSON from your Python dictionaries, and format it for humans or machines. Continue practicing and explore more beginner-friendly guides at CodDesire Python.