.dump()

The .dump() function encodes a Python object as a JSON file. The process is known as serialization. The encoding conversion is based on this table. This function is essential for data persistence, APIs, and inter-process communication where data needs to be stored or transferred in a structured, language-independent format.

Syntax

json.dump(obj, file, *, skipkeys=False, ensure_ascii=True, indent=None, ...)

Parameters:

• obj: The Python object to be converted. It can be a string, list, dictionary, etc.
• file: A file-like object opened in write mode ('w').
• skipkeys (Optional): If True, skips dictionary keys that are not basic data types instead of raising a TypeError.
• ensure_ascii (Optional): If True, escapes all non-ASCII characters; set to False for UTF-8 encoded output.
• indent (Optional): If set to an integer (e.g., 2 or 4), pretty-prints the output with that many spaces of indentation.

Note: The ellipsis (...) in the syntax indicates that there can be additional optional parameters beyond those listed here.

Example 1: Basic Usage of .dump()

In this example, a Python dictionary is serialized into a JSON-formatted text file named person.json using .dump():

import json

person = {
  'name': 'Alice',
  'age': 30,
  'city': 'New York'
}

with open('person.json', 'w') as f:
  json.dump(person, f)

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Example 2: .dump() with Indentation and Non-ASCII Characters

This example writes a dictionary containing non-ASCII characters to a file using .dump(). The ensure_ascii=False parameter ensures characters are saved in UTF-8 format without being escaped, while indent=4 makes the output nicely formatted for readability:

import json

product = {
  'name': 'Café Latte',
  'price': 3.5,
  'available': True,
  'tags': ['coffee', 'beverage', 'café']
}

with open('product.json', 'w') as f:
  json.dump(product, f, indent=4, ensure_ascii=False)

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Example 3: Serializing a List of Dictionaries Using .dump()

This example shows how to use .dump() to serialize more complex structures like a list of dictionaries into JSON format:

import json

users = [
  {'id': 1, 'name': 'Alice'},
  {'id': 2, 'name': 'Bob'}
]

with open('users.json', 'w') as f:
  json.dump(users, f, indent=2)

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Frequently Asked Questions

1. What is the difference between .dump() and .dumps() in Python?

• .dump() writes serialized data to a file-like object.
• .dumps() returns the serialized data as a string.

2. Can I use .dump() with custom objects?

Not directly. You’ll need to define a custom serialization function or use default=str to handle non-serializable objects.

3. What happens if the file used in .dump() does not exist?

If the file used in .dump() is opened in write mode ('w'), Python will create the file automatically. If the directory path doesn’t exist, it will raise a FileNotFoundError.