json.dump() in Python

json.dump() method in Python is used to serialize a Python object into a JSON formatted string and write it directly into a file. This method is part of the built-in json module, which is useful when you need to save Python data structures like dictionaries or lists in JSON format.

Syntax

json.dump(obj, file, skipkeys=False, ensure_ascii=True, check_circular=True, allow_nan=True, cls=None, indent=None, separators=None)

Parameters:

• obj: The Python object (e.g., dictionary, list) to convert to JSON.
• file: The file-like object where the JSON data will be written.
• skipkeys: If True, non-serializable keys will be ignored. Default is False.
• ensure_ascii: If True, all non-ASCII characters are escaped. If False, non-ASCII characters are written as-is. Default is True.
• check_circular: If True, checks for circular references. Default is True.
• allow_nan: If True, allows NaN, Infinity, and -Infinity values in JSON. Default is True.
• cls: A custom JSON encoder class. Default is None.
• indent: Specifies the number of spaces for indentation to improve readability. Default is None.
• separators: A tuple that defines how the items in the JSON file will be separated. Default is (', ', ': ').

Let's look at some examples:

Example 1: Writing JSON Data to a File with Indentation

In this example, we will demonstrate how to write Python data to a JSON file while formatting it with indentation for better readability.

import json data = { "emp1": {"name": "Lisa", "age": 34, "salary": 54000}, "emp2": {"name": "Elis", "age": 24, "salary": 40000}, } # Writing to a JSON file with indentation with open("output.json", "w") as outfile: json.dump(data, outfile, indent=4) 

Output:

Example 2: Using skipkeys to Ignore Non-Serializable Keys

This example demonstrates how to use the skipkeys parameter to prevent errors when attempting to serialize non-serializable keys, like tuples.

import json data = {("address", "street"): "Brigade Road"} # Tuple as key # Writing to a JSON file with skipkeys=True with open("output.json", "w") as outfile: json.dump(data, outfile, skipkeys=True) 

Output:

{}

In the above example, the tuple ("address", "street") is ignored because it's not serializable, and no error is raised due to skipkeys=True.

Example 3: Writing Non-ASCII Characters

Here, we will demonstrate how to handle non-ASCII characters in the JSON output by setting ensure_ascii=False.

import json data = {"greeting": "¡Hola Mundo!"} # Writing to a JSON file with ensure_ascii=False to preserve non-ASCII characters with open("output.json", "w", encoding="utf8") as outfile: json.dump(data, outfile, ensure_ascii=False) 

Output:

{

"greeting": "¡Hola Mundo!"

}

With ensure_ascii=False, the special characters are written as-is without being escaped.

Example 4: Writing JSON with NaN and Infinity Values

This example shows how to handle special floating-point values like NaN and Infinity by adjusting the allow_nan parameter.

import json data = {"value": float("nan"), "infinity": float("inf")} # Writing to a JSON file with allow_nan=True with open("output.json", "w") as outfile: json.dump(data, outfile, allow_nan=True) 

Output:

{

"value": NaN,

"infinity": Infinity

}

By setting allow_nan=True, we can serialize special float values like NaN and Infinity.

Difference between dump() and dumps()