rohitg00/ai-engineering-from-scratch · error · ValueError

expected (B, Nt, hidden), got {tuple(x.shape)}

Error message

expected (B, Nt, hidden), got {tuple(x.shape)}

What it means

Error "expected (B, Nt, hidden), got {tuple(x.shape)}" thrown in rohitg00/ai-engineering-from-scratch.

Source

Thrown at phases/19-capstone-projects/61-cross-attention-fusion/code/main.py:109

        self.q_proj = nn.Linear(cfg.hidden, cfg.hidden, bias=True)
        self.kv_proj = nn.Linear(cfg.vision_dim, cfg.hidden * 2, bias=True)
        self.out = nn.Linear(cfg.hidden, cfg.hidden, bias=True)
        self.drop = nn.Dropout(cfg.dropout)
        self.scale = 1.0 / math.sqrt(cfg.head_dim)

    def project_memory(self, memory: torch.Tensor) -> tuple[torch.Tensor, torch.Tensor]:
        if memory.dim() != 3:
            raise ValueError(f"expected (B, Nv, vision_dim), got {tuple(memory.shape)}")
        b, nv, _ = memory.shape
        h, hd = self.cfg.heads, self.cfg.head_dim
        kv = self.kv_proj(memory).reshape(b, nv, 2, h, hd).permute(2, 0, 3, 1, 4)
        return kv[0], kv[1]

    def forward(self, x: torch.Tensor, memory: torch.Tensor,
                kv_cache: tuple[torch.Tensor, torch.Tensor] | None = None
                ) -> torch.Tensor:
        if x.dim() != 3:
            raise ValueError(f"expected (B, Nt, hidden), got {tuple(x.shape)}")
        if memory.shape[0] != x.shape[0]:
            raise ValueError(
                f"batch mismatch: text {x.shape[0]} vs memory {memory.shape[0]}"
            )
        b, nt, d = x.shape
        h, hd = self.cfg.heads, self.cfg.head_dim

        q = self.q_proj(x).reshape(b, nt, h, hd).transpose(1, 2)
        if kv_cache is None:
            k, v = self.project_memory(memory)
        else:
            k, v = kv_cache
            expected = (b, h, memory.shape[1], hd)
            if k.shape != expected or v.shape != expected:
                raise ValueError(
                    f"kv_cache must be (B,H,Nv,hd)={expected}, got "
                    f"k={tuple(k.shape)} v={tuple(v.shape)}"
                )

View on GitHub (pinned to 39ea8a1c6d)

When it happens

Trigger: Thrown at phases/19-capstone-projects/61-cross-attention-fusion/code/main.py:109 when the library encounters an invalid state.

Common situations: See trigger scenarios.

AI-assisted analysis of rohitg00/ai-engineering-from-scratch@39ea8a1c6d (2026-08-26). Data as JSON: /api/errors/e7284716fae0c49a. Report an issue: GitHub.