Phi-4-MM Bad Operand Type Error

Overview

When running sample_inference_phi4mm.py, an error of the form:

TypeError: bad operand type for unary -: 'NoneType'

could appear if num_logits_to_keep is None. This occurs because Python cannot evaluate [start: -num_logits_to_keep] when num_logits_to_keep has no value.

Root Cause

In the model code (typically found in modeling_phi4mm.py), there is a slice operation:

logits = self.lm_head(hidden_states[:, -num_logits_to_keep:, :])

If num_logits_to_keep is None, the unary - operator triggers the error.

Fix

Ensure num_logits_to_keep is assigned before slicing. Below is an example fix:

# filepath: ...microsoft--Phi-4-multimodal-instruct/modeling_phi4mm.py
# ...existing code...

if num_logits_to_keep is None:
    num_logits_to_keep = hidden_states.size(1)

logits = self.lm_head(hidden_states[:, -num_logits_to_keep:, :])

# ...existing code...

This ensures num_logits_to_keep always has a valid numeric value before the slice is computed. Once applied, test_phi4_multi.py should run without the "bad operand type" error.