Python UUID Generator

Universally Unique Identifiers (UUIDs) are 128-bit numbers used to uniquely identify information in computer systems. Generating unique IDs is a fundamental task in many software applications, from database primary keys to distributed system coordination. This challenge will guide you in implementing a basic UUID generator in Python.

Problem Description

Your task is to create a Python function that generates a UUID. For this challenge, you will focus on implementing a simplified version of a UUID, specifically a variant that combines random elements with a timestamp.

What needs to be achieved: Implement a Python function generate_uuid() that returns a string representing a unique identifier.

Key requirements:

1. The generated UUID should be a string.
2. The UUID should follow a specific format: xxxxxxxx-xxxx-Mxxx-Nxxx-xxxxxxxxxxxx, where:
   • x represents a hexadecimal digit (0-9, a-f).
   • M indicates the UUID version. For this challenge, it will always be 4 (representing a randomly generated UUID).
   • N indicates the variant. For this challenge, it will always be one of 8, 9, a, or b.
3. The UUID should be generated by combining random hexadecimal characters with a timestamp component.
4. The function should be callable multiple times, with each call producing a distinct UUID.

Expected behavior: When generate_uuid() is called, it should return a string that looks like a UUID, adhering to the specified format and incorporating randomness and a timestamp-like element.

Edge cases to consider:

• Uniqueness: While true randomness is hard to guarantee with simple methods, the generated IDs should be highly likely to be unique across multiple calls.

Examples

Example 1:

Input: None
Output: "f47ac10b-58cc-4372-a567-0e02b2c3d479"
Explanation: A sample UUID generated by the function. The '4' indicates version 4, and the first hex digit after the second hyphen ('a') indicates a valid variant.

Example 2:

Input: None
Output: "123e4567-e89b-42d3-a09f-1234567890ab"
Explanation: Another sample UUID. Note the different random characters and the variant indicator 'a'.

Example 3:

Input: None
Output: "00000000-0000-4000-9000-000000000000"
Explanation: While unlikely, a UUID with all zeros in its random parts is theoretically possible. The version is correctly set to '4', and the variant starts with '9'.

Constraints

• The generated UUID string must be exactly 36 characters long.
• The characters used must be hexadecimal digits (0-9, a-f).
• The version digit (M) must be '4'.
• The variant digit (N) must be one of '8', '9', 'a', or 'b'.
• You can use standard Python libraries, but avoid directly using the uuid module for the core generation logic.

Notes

• Think about how to represent the 128 bits of a UUID. You'll need to generate a total of 32 hexadecimal characters.
• The hyphen separators are fixed at specific positions.
• Consider how to incorporate a timestamp-like element. The current time in milliseconds or nanoseconds could be a good starting point, but you'll need to convert it into hexadecimal.
• For the variant part, you can use bitwise operations or simple conditional logic to ensure the correct bits are set. A quick search for "UUID variant 1" will reveal the bit patterns. For simplicity, focus on ensuring the first hexadecimal digit of the variant part is 8, 9, a, or b.
• You will need to generate random hexadecimal characters for the majority of the UUID. Python's random module will be helpful.