Python Write JSON Data to a File?

How do I write JSON data to a file in Python? You can easily write JSON data to a file using the built-in Python json module. To write JSON data to a file use the json.dump() method. Besides this method, there are more methods as well which we will discuss in this article along with examples.

1. Quick Examples of Writing JSON data to a File

These are some quick examples to give you a high-level idea of how to wirte a JSON data to a file and we will discuss each of these methods in detail later on.


# Quick Examples of Writing JSON data to a File

# Import
import json

# Write dictionary to file using json.dump()
file_path = "data.json"
with open(file_path, "w") as f:
    json.dump(data, f)

# Write JSON data with Unicode characters to file
file_path = "unicode_data.json"
with open(file_path, "w", encoding="utf-8") as f:
    json.dump(data, f, ensure_ascii=False)

2. What is JSON Data?

JSON (JavaScript Object Notation) is a format used to represent data in a way that is easy for both humans and machines to understand. It is commonly used to transmit data between web applications and servers. JSON is based on a subset of the JavaScript programming language, so if you're familiar with JavaScript, you'll find JSON easy to understand.

In JSON, data is represented using a simple key-value pair structure. The keys represent the names of fields or attributes of the data, while the values represent the actual data itself. JSON data can be represented as a string and can be easily converted to a Python dictionary or list using the built-in json module.

Below is a sample JSON. We will use this JSON throughout our examples:


json_data = {
    "name": "Python",
    "year": 1991,
    "creator": "Guido van Rossum",
    "popular": True
}

3. Using json.dump() to Write JSON Data to a File

The json.dump() method is used to write JSON data to a file in Python. It takes two arguments, the data to be written, and the file object to write to.

Following is the syntax of the json.dump() method.


# Import json module
import json

# Write data to object file
json.dump(data, file_object)

Here,

data - Any object with JSON data
file_object - File object where to write JSON data

3.1 Write Data to JSON File

Let's see an example of writing a Python object to a JSON file. The data parameter represents the JSON data to be written to the file. This can be any Python object that is JSON serializable, such as a dictionary or a list. Here, in the below example json_data is a dictionary object which I will write to a file. Alternatively, you can also put this data to a file and read json from a file into a object.

See the below example:


# Import json module
import json

# Create dictionary object which is json representation
json_data = {
    "name": "Python",
    "year": 1991,
    "creator": "Guido van Rossum",
    "popular": True
}

# Writing JSON data to a file using a file object
with open("data.json", "w") as outfile:
    # json_data refers to the above JSON
    json.dump(json_data, outfile)

Though this is the simplest way to write JSON data to a file. However, there is more to this method. There are more parameters of this method. Below is the complete syntax of the json.dump() function:


# json.dump() Syntax
json.dump(obj, fp, *, skipkeys=False, ensure_ascii=True, 
    check_circular=True, allow_nan=True, cls=None, indent=None, 
    separators=None, default=None, sort_keys=False, **kw
)

We have seen only two required parameters of this method, however, we can always use those optional parameters when necessary. Let's see a few of them right here.

3.2 skipkeys Parameter of json.dump()

The skipkeys parameter is a boolean value that determines whether keys that are not JSON serializable should be skipped (True) or raise a TypeError (False). The default value is False.

Let's make the skipkeys value True and see the result.


import json

data ={
    "name": "Python",
    (1, 2): 1991,
    "creator": "Guido van Rossum",
    "popular": True
}

# Example with skipkeys=True
with open("data.json", "w") as outfile:
    json.dump(data, outfile, skipkeys=True)

Yields the below output, because the JSON object is not serializable.


# Output:
raise TypeError(f'keys must be str, int, float, bool or None, '
TypeError: keys must be str, int, float, bool or None, not tuple

3.3 "ensure_ascii" Paramter of json.dump()

The ensure_ascii parameter is a boolean value that determines whether non-ASCII characters should be escaped (False) or represented as ASCII characters (True). The default value is True.


import json

data = {"name": "John", "age": 30, "city": "New York"}

# Example with ensure_ascii=True (default)
with open("data.json", "w") as outfile:
    json.dump(data, outfile)

Remaining of the parameters are also adding other functionality which you can try. Below are one-line explanation of each of the parameters.

check_circular: A Boolean value specifying whether to check for circular references in the Python object. Default is True.
allow_nan: A Boolean value specifying whether to allow NaN, Infinity, and -Infinity values. The default is True.
cls: A custom encoder class used to convert non-JSON serializable objects into JSON serializable objects.
indent: An integer value representing the number of spaces used for indentation. If None, the output JSON will be compact.

4. json.dumps() - Output JSON to a File

The json.dumps() function is very much similar to Python json.dump() function which can also be used to write to a JSON file. However, json.dumps() is a method to serialize Python objects to a JSON formatted string, not to write JSON data to a file. We can use this method in combination with the write() method of a file object to write the JSON formatted string to a file.

Related: How to write a file in Python?

See the below example:


import json

# Serialize the Python object to a JSON formatted string
json_data = json.dumps(data)

# Write the JSON formatted string to a file
file_path = "example.json"
with open(file_path, "w") as outfile:
    outfile.write(json_data)

5. Write JSON having UNICODE to a File

When you write JSON data that contains Unicode characters to a file using Python's built-in json.dump(), by default, the Unicode characters will be escaped. You can use the codecs.open() method to open the file with the specified encoding and then write the JSON data to the file as a string.


import codecs, json

# Write the dictionary to a file with Unicode characters
file_path = "data.json"
with codecs.open(file_path, "w", encoding="utf-8") as f:
    f.write(json.dumps(data, sort_keys=True, ensure_ascii=False))

6. Summary and Conclusion

In this article, you have learned how to write JSON data to a file in Python. We have discussed different methods with examples. I hope this article was helpful. If you have any questions, you can ask them in the comment section below.

Happy Coding!