Experiment Traffic Splitter

Assign users to weighted experiment variants with stable deterministic bucketing.

Requirements

• Define assign_variant(user_id, experiment_key, variants).
• variants is a list of (name, weight) tuples.
• Ignore variants with weight 0.
• Use a stable bucket derived from experiment_key and user_id.
• Return the selected variant name.
• Return None if total positive weight is 0.
• Changing experiment_key can change assignment.
• Calling the function repeatedly with the same inputs must return the same variant.

Example

Constraints

• Do not use Python's built-in hash, because it is process-randomized.
• Do not use randomness.
• Preserve variant order for bucket ranges.