{"record":{"id":"7f6ad7b64ebed2ec","repo":"rohitg00/ai-engineering-from-scratch","slug":"expected-b-n-d-got-tuple-x-shape","errorCode":null,"errorMessage":"expected (B, N, D), got {tuple(x.shape)}","messagePattern":"expected \\(B, N, D\\), got (.+?)","errorType":"validation","errorClass":"ValueError","httpStatus":null,"severity":"error","filePath":"phases/19-capstone-projects/59-vit-transformer/code/main.py","lineNumber":86,"sourceCode":"            patch_size=self.patch_size,\n            in_channels=self.in_channels,\n            hidden=self.hidden,\n        )\n\n\nclass MultiHeadSelfAttention(nn.Module):\n    def __init__(self, cfg: ViTConfig) -> None:\n        super().__init__()\n        self.cfg = cfg\n        self.qkv = nn.Linear(cfg.hidden, cfg.hidden * 3, bias=True)\n        self.out = nn.Linear(cfg.hidden, cfg.hidden, bias=True)\n        self.drop = nn.Dropout(cfg.dropout)\n        self.scale = 1.0 / math.sqrt(cfg.head_dim)\n        self.last_attn: torch.Tensor | None = None\n\n    def forward(self, x: torch.Tensor, store_attn: bool = False) -> torch.Tensor:\n        if x.dim() != 3:\n            raise ValueError(f\"expected (B, N, D), got {tuple(x.shape)}\")\n        b, n, d = x.shape\n        h = self.cfg.heads\n        hd = self.cfg.head_dim\n\n        qkv = self.qkv(x).reshape(b, n, 3, h, hd).permute(2, 0, 3, 1, 4)\n        q, k, v = qkv[0], qkv[1], qkv[2]\n\n        scores = (q @ k.transpose(-2, -1)) * self.scale\n        attn = F.softmax(scores, dim=-1)\n        if store_attn:\n            self.last_attn = attn.detach()\n\n        out = attn @ v\n        out = out.transpose(1, 2).reshape(b, n, d)\n        out = self.out(out)\n        out = self.drop(out)\n        return out\n","sourceCodeStart":68,"sourceCodeEnd":104,"githubUrl":"https://github.com/rohitg00/ai-engineering-from-scratch/blob/39ea8a1c6d0b61f071226eff7ede4d4105fed820/phases/19-capstone-projects/59-vit-transformer/code/main.py#L68-L104","documentation":"Error \"expected (B, N, D), got {tuple(x.shape)}\" thrown in rohitg00/ai-engineering-from-scratch.","triggerScenarios":"Thrown at phases/19-capstone-projects/59-vit-transformer/code/main.py:86 when the library encounters an invalid state.","commonSituations":"See trigger scenarios.","solutions":[],"exampleFix":null,"handlingStrategy":null,"validationCode":null,"typeGuard":null,"tryCatchPattern":null,"preventionTips":[],"tags":[],"backgroundTag":null,"analyzedSha":"39ea8a1c6d0b61f071226eff7ede4d4105fed820","analyzedAt":"2026-08-26T03:13:46.626Z","schemaVersion":2},"datasetVersion":"2026-08-26T07:17:17.940Z"}