Working with JSON files in Python - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Reading JSON data from a file

What is the output of this Python code that reads a JSON file and prints the data?

Python

import json
with open('data.json', 'r') as file:
    data = json.load(file)
print(data)

A {'name': 'Alice', 'age': 30}

B "{'name': 'Alice', 'age': 30}"

C SyntaxError

D FileNotFoundError

💡 Hint

Remember json.load reads JSON and converts it to Python objects.

json.load reads the JSON file and converts it to a Python dictionary. The print statement outputs the dictionary.

❓ Predict Output

intermediate

Writing Python dictionary to JSON file

What will be the content of 'output.json' after running this code?

Python

import json
data = {'city': 'Paris', 'population': 2148327}
with open('output.json', 'w') as f:
    json.dump(data, f)

A {"city": "Paris", "population": 2148327}

B {'city': 'Paris', 'population': 2148327}

C SyntaxError

D TypeError

💡 Hint

json.dump writes JSON formatted string to file with double quotes.

json.dump converts the dictionary to a JSON string with double quotes and writes it to the file.

❓ Predict Output

advanced

Handling JSON decoding errors

What error will this code raise when trying to load invalid JSON content?

Python

import json
invalid_json = '{"name": "Bob", age: 25}'
data = json.loads(invalid_json)

A TypeError

B No error, data is loaded

C KeyError

D json.decoder.JSONDecodeError

💡 Hint

JSON keys must be in double quotes.

The JSON string is invalid because the key 'age' is not in double quotes, causing JSONDecodeError.

❓ Predict Output

advanced

Using json.dumps with indentation

What is the output of this code?

Python

import json
data = {'fruit': 'apple', 'count': 5}
result = json.dumps(data, indent=2)
print(result)

A {"fruit": "apple", "count": 5}

B

{
  "fruit": "apple",
  "count": 5
}

C SyntaxError

D TypeError

💡 Hint

indent=2 adds line breaks and spaces for readability.

json.dumps with indent=2 formats the JSON string with new lines and two spaces indentation.

🧠 Conceptual

expert

Understanding JSON serialization of custom objects

What happens when you run this code?

Python

import json
class Person:
    def __init__(self, name):
        self.name = name
p = Person('Eve')
json.dumps(p)

A {"name": "Eve"}

B "{'name': 'Eve'}"

C TypeError: Object of type Person is not JSON serializable

D No output, code runs silently

💡 Hint

json.dumps can only serialize basic Python types by default.

Custom objects like Person are not serializable by default, causing TypeError.

Practice

1.

What is the main purpose of using JSON files in Python programs?

easy

A. To create graphical user interfaces

B. To execute Python code faster

C. To save and load data in a simple text format

D. To compile Python programs into executables

Solution

1. Step 1: Understand JSON file usage

   JSON files store data in a text format that is easy to read and share.

2. Step 2: Identify the correct purpose

   Saving and loading data simply matches the main use of JSON files in Python.

3. Final Answer:

   To save and load data in a simple text format -> Option C

4. Quick Check:

   JSON files = data storage [OK]

Hint: JSON files store data simply as text [OK]

Common Mistakes:

• Thinking JSON speeds up code execution
• Confusing JSON with GUI creation
• Assuming JSON compiles code

2.

Which of the following is the correct way to open a JSON file named data.json for reading in Python?

easy

A. open('data.json', 'r')

B. open('data.json', 'w')

C. open('data.json', 'a')

D. open('data.json', 'x')

Solution

1. Step 1: Understand file modes

   'r' mode opens a file for reading, 'w' for writing, 'a' for appending, 'x' for creating new file.

2. Step 2: Choose mode for reading JSON

   To read JSON data, the file must be opened in 'r' mode.

3. Final Answer:

   open('data.json', 'r') -> Option A

4. Quick Check:

   Read mode = 'r' [OK]

Hint: Use 'r' mode to read files [OK]

Common Mistakes:

• Using 'w' which overwrites the file
• Using 'a' which appends data
• Using 'x' which fails if file exists

3.

What will be the output of the following Python code?

import json

with open('data.json', 'w') as f:
    json.dump({'name': 'Alice', 'age': 30}, f)

with open('data.json', 'r') as f:
    data = json.load(f)
print(data['age'])

medium

A. Alice

B. 30

C. {'name': 'Alice', 'age': 30}

D. Error: file not found

Solution

1. Step 1: Write dictionary to JSON file

   The code writes {'name': 'Alice', 'age': 30} to 'data.json' using json.dump.

2. Step 2: Read JSON file and access 'age'

   json.load reads the file back as a dictionary, then data['age'] accesses the value 30.

3. Final Answer:

   30 -> Option B

4. Quick Check:

   data['age'] = 30 [OK]

Hint: json.load returns Python dict from JSON file [OK]

Common Mistakes:

• Expecting string output instead of integer
• Confusing json.dump and json.load usage
• Assuming file read fails without writing first

4.

Identify the error in this code snippet that tries to read JSON data from a file:

import json

f = open('data.json', 'r')
data = json.load(f)
f.close()
print(data)

medium

A. Missing import statement for json

B. File not opened in write mode

C. File not closed properly

D. No error, code works correctly

Solution

1. Step 1: Check import and file open

   The code imports json and opens the file in 'r' mode correctly.

2. Step 2: Verify json.load and file close

   json.load reads JSON data properly, and file is closed with f.close().

3. Final Answer:

   No error, code works correctly -> Option D

4. Quick Check:

   Code reads JSON file correctly [OK]

Hint: json.load needs file opened in 'r' mode [OK]

Common Mistakes:

• Forgetting to import json
• Opening file in wrong mode
• Not closing the file after reading

5.

You want to save a Python dictionary {'a': 1, 'b': 2, 'c': 3} to a JSON file and then read it back. Which code snippet correctly does this and prints the value of key 'b'?

hard

A. import json
with open('file.json', 'w') as f:
json.dump({'a': 1, 'b': 2, 'c': 3}, f)
with open('file.json', 'r') as f:
data = json.load(f)
print(data['b'])

B. import json
with open('file.json', 'r') as f:
json.dump({'a': 1, 'b': 2, 'c': 3}, f)
with open('file.json', 'w') as f:
data = json.load(f)
print(data['b'])

C. import json
f = open('file.json', 'w')
json.load({'a': 1, 'b': 2, 'c': 3}, f)
f.close()
f = open('file.json', 'r')
data = json.dump(f)
f.close()
print(data['b'])

D. import json
with open('file.json', 'w') as f:
json.load({'a': 1, 'b': 2, 'c': 3}, f)
with open('file.json', 'r') as f:
data = json.dump(f)
print(data['b'])

Solution

1. Step 1: Write dictionary to JSON file correctly

   json.dump writes Python dict to file opened in 'w' mode.

   import json
   with open('file.json', 'w') as f:
       json.dump({'a': 1, 'b': 2, 'c': 3}, f)
   with open('file.json', 'r') as f:
       data = json.load(f)
   print(data['b'])

   does this correctly.

2. Step 2: Read JSON file and access key 'b'

   json.load reads JSON back from file opened in 'r' mode, then data['b'] prints 2.

3. Final Answer:

   Code in Option A correctly saves and reads JSON, printing 2 -> Option A

4. Quick Check:

   json.dump to write, json.load to read [OK]

Hint: Use json.dump to write, json.load to read JSON files [OK]

Common Mistakes:

• Using json.load to write data
• Using json.dump to read data
• Opening files in wrong modes