json.dump vs json.dumps

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The 's' stands for 'string'. json.dumps(obj) serializes obj and returns a Python str. json.dump(obj, f) serializes obj and writes the result to the file-like object f, equivalent to f.write(json.dumps(obj)) but without building the whole string in memory first. In practice: use json.dump when writing to a file (more efficient, no intermediate string), and json.dumps when you need the JSON as a string - for example, to embed it in a response body or store it in a database column. Both accept the same keyword arguments: indent for pretty-printing, sort_keys to stabilize key order, and default for a custom serializer function to handle types like datetime or numpy scalars that the standard encoder doesn't know about.