Merge Dictionaries in Python

ADP Workforce Now may combine default and employee-specific configuration values before processing a request. Implement a function that merges two Python dictionaries into a new dictionary.

If both dictionaries contain the same key, the value from updates must override the value from defaults. Do not modify either input dictionary. This is a shallow merge, so nested dictionaries should be treated as ordinary values rather than merged recursively.

Formal Specification

Implement merge_dicts(defaults, updates).

• Input: Two dictionaries whose keys are hashable Python values and whose values may be any Python objects.
• Output: A new dictionary containing every key from both inputs.
• Collision rule: For duplicate keys, use the value from updates.
• Mutation rule: Leave defaults and updates unchanged.