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Sameer Qaiser
Sameer Qaiser

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Python JSON: Working with Data Files

#json #python #beginners #programming

📌 Quick Info

  • Topic: Working with JSON in Python
  • Target Audience: Beginners who know files and dictionaries
  • Goal: Understand how to save and load structured data

1. Introduction

"I could write text to a file. But what if I needed to save a whole dictionary? A list of users? A config file? That's when I learned about JSON — and now it's how every one of my projects saves data."

2. The Problem (Saving Complex Data to a Text File) 

user = {"name": "Ali", "age": 25, "city": "Karachi"}

with open("user.txt", "w") as file:
    file.write(str(user))
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What’s in the file:

{'name': 'Ali', 'age': 25, 'city': 'Karachi'}
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Problem: It’s ugly. It’s not standard. Other programs can’t read it easily.

3. The Solution (JSON) 

import json

user = {"name": "Ali", "age": 25, "city": "Karachi"}

with open("user.json", "w") as file:
    json.dump(user, file)
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What’s in the file:

{"name": "Ali", "age": 25, "city": "Karachi"}
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Clean. Standard. Readable by almost any language.

4. Reading JSON Back 

import json

with open("user.json", "r") as file:
    user = json.load(file)

print(user["name"])   # Ali
print(user["age"])    # 25
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The Dictionary comes back exactly as it was saved.

5. How It Works (Line By Line)

import json — Loads Python’s built-in JSON module.

json.dump(data, file) — Writes a Python object to a file as JSON.

json.load(file) — Reads JSON from a file back into a Python object.

json.dumps(data) — Converts a Python object to a JSON string (instead of writing to a file).

json.loads(string) — Parses a JSON string into Python.

6. JSON vs Python: What Maps to What

Python JSON
dict Object
List Array
str string
int/ float number
True / False true / false
None null

The names are different, but the structure is the same.

7. Real Example (My Practice) 

import json

users = [
    {"name": "Ali", "score": 85},
    {"name": "Sara", "score": 92},
    {"name": "Ahmed", "score": 78}
]

with open("scores.json", "w") as file:
    json.dump(users, file, indent=2)

with open("scores.json", "r") as file:
    loaded = json.load(file)

for user in loaded:
    print(f"{user['name']}: {user['score']}")
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Output: 

Ali: 85
Sara: 92
Ahmed: 78
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The indent=2 makes the file human-readable.

8. Common Mistakes Beginners Make

Mistake 1: Forgetting to import json 

json.dump(...)
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Mistake 2: Confusing dump and dumps

  • json.dump(): writes to a file
  • json.dumps(): returns a string

Mistake 3: Trying to save non-JSON types 

import json
json.dumps({"date": datetime.now()})
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JSON only supports basic types. Convert to strings first.

9. What I learned

-) JSON is the standard for saving structured data
-) json.dump() writes to a file, json.load() reads from it
-) json.dumps() and json.loads() work with strings
-) indent=2 makes files human-readable
-) Not everything can be saved — only dicts, lists, strings, numbers, booleans, and None

10. Conclusion

“JSON solved a problem I didn't know I had. Now every project I build saves its data as JSON — because it's readable, portable, and just works. Once you learn it, you'll never go back to saving dictionaries as text.”

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