Using json.loads()

To easily convert an input JSON string to a dictionary, use the json.loads() method in Python.

Let’s take a new string that consists of JSON data and convert it into a dictionary, and then verify the data type using the type() method.

import json

json_string = '{"student_name": "Smith", "age": 15, "country": "USA"}'

# Convert JSON string to dictionary
dict = json.loads(json_string)

print(dict)
# Output: {'student_name': 'Smith', 'age': 15, 'country': 'USA'}

print(type(dict))
# Output: <class 'dict'>

Nested JSON string

What if the string contains nested json data? Well, it will return a nested dictionary.

import json

json_string = '{"student_name": "Smith", "personal_info": {"age": 15, "country": "USA"}}'

dict = json.loads(json_string)

print(dict)
# Output: {'student_name': 'Smith', 'personal_info': {'age': 15, 'country': 'USA'}}

print(type(dict))
# Output: <class 'dict'>

Handling JSON Arrays

If your input is a nested array (list of objects), Python will convert it to a list of dictionaries.

import json

# JSON array
json_string = '''[
    {"id": 1, "name": "Krunal"},
    {"id": 2, "name": "Ankit"}
]'''

# Convert to list of dictionaries
dictionary = json.loads(json_string)

# Access data
print(dictionary[0]['name'])
# Output: Krunal

print(dictionary[1]['id'])
# Output: 2

You can see from the above output that each element in the list can be a dictionary, allowing iteration or indexed access.

Converting JSON from an API Response

When you fetch the JSON from an API, you can use the “requests” module to get the JSON string and parse it. The requests library’s .json() method internally uses json.loads() method to convert the API’s JSON response to a dictionary.

import requests

# Example API (public API for testing)
response = requests.get('https://jsonplaceholder.typicode.com/users/5')
json_data = response.json()  # Automatically parses JSON to dictionary

# Accessing data
print(json_data['name'])  
# Output: Chelsey Dietrich

Invalid JSON

If the input JSON string has a syntax error, it will raise a json.JSONDecodeError.

import json

# Invalid JSON (missing quotes around key)
json_string = '{name: "Krunal", "age": 32}'

try:
    dictionary = json.loads(json_string)
except json.JSONDecodeError as e:
    print(f"Error: {e}")

# Output: Error: Expecting property name enclosed in double quotes: line 1 column 2 (char 1)

Empty or Null JSON

What if an input is an empty JSON or contains Null values? An empty json string will return an empty json, and a JSON of null will return None.

import json

# Empty JSON object
json_string = '{}'
dictionary = json.loads(json_string)
print(dictionary)
# Output: {}

# JSON with null
json_string = '{"name": null, "age": 30}'
dictionary = json.loads(json_string)
print(dictionary['name'])
# Output: None

Unicode and special characters

JSON data often contains special characters in real-life scenarios. Python handles special and unicode characters automatically if they are in the input json data.

import json

# JSON with Unicode
json_string = '{"name": "José", "city": "São Paulo"}'

dictionary = json.loads(json_string)

print(dictionary['name'])
# Output: José

Handling missing keys

What if your input data contains missing keys in JSON? If you convert it to a dictionary, it may raise a KeyError.

To handle the potential error, we can use the dict.get() method. The dict.get(key, default) method returns the value if key exists; otherwise, returns default. This prevents KeyError.

import json

json_string = '{"name": "Krunal", "age": 30, "city": "New York"}'
dict = json.loads(json_string)

# Handle missing keys safely using .get() with a default value
print(dict.get('age', 0))        
# Output: 30 (existing key)

print(dict.get('salary', 0))     
# Output: 0 (missing key, default used)

In the case of the “salary” key, it does not exist; however, we have already passed the default value, which is 0. So, the output is 0, even if the key is missing. So, it handled the potential error.

Using json.load()

If your input is a file, you can load it using json.load() method.

The built-in JSON module function json.load() method reads a JSON data directly from a file.

import json

# Open the JSON file for reading
with open('data.json') as file:
    # Use json.load() to read the file and convert it to a dictionary
    dict = json.load(file)

print(dict)
# Output: {'student_name': 'Smith', 'age': 22, 'country': 'USA'}

print(type(dict))
# Output: <class 'dict'>

Nested JSON File

What if the file contains nested json data? Well, let’s find out.

Below is the nested_data.json file.

import json

# Open the Nested JSON file for reading
with open('nested_data.json') as file:
    # Use json.load() to read the file and convert it to a dictionary
    dict = json.load(file)

print(dict)
# Output: {'student_name': 'Smith', 'personal_info': {'age': 22, 'country': 'USA'}}

print(type(dict))
# Output: <class 'dict'>

That’s it.