tensorflow/models · error · ValueError

Block fn `{}` is not supported.

Error message

Block fn `{}` is not supported.

What it means

Error "Block fn `{}` is not supported." thrown in tensorflow/models.

Source

Thrown at official/vision/modeling/backbones/resnet_unet.py:397

              x)
      x = self._norm(
          axis=bn_axis,
          momentum=norm_momentum,
          epsilon=norm_epsilon,
          trainable=bn_trainable)(
              x)
      x = tf_utils.get_activation(activation, use_keras_layer=True)(x)
    else:
      x = layers.MaxPool2D(pool_size=3, strides=2, padding='same')(x)

    endpoints = {}
    for i, spec in enumerate(RESNET_SPECS[model_id]):
      if spec[0] == 'residual':
        block_fn = nn_blocks.ResidualBlock
      elif spec[0] == 'bottleneck':
        block_fn = nn_blocks.BottleneckBlock
      else:
        raise ValueError('Block fn `{}` is not supported.'.format(spec[0]))
      x = self._block_group(
          inputs=x,
          filters=int(spec[1] * self._depth_multiplier),
          strides=(1 if i == 0 else 2),
          block_fn=block_fn,
          block_repeats=spec[2],
          stochastic_depth_drop_rate=nn_layers.get_stochastic_depth_rate(
              self._init_stochastic_depth_rate, i + 2, 8),
          name='block_group_l{}'.format(i + 2))
      endpoints[str(i + 2)] = x

    norm_layer = lambda: tf_keras.layers.LayerNormalization(epsilon=1e-6)
    for i in range(len(upsample_filters)):  # pyrefly: ignore[bad-argument-type]
      backbone_feature = layers.Conv2D(
          filters=int(upsample_filters[i] * stem_depth_multiplier),  # pyrefly: ignore[unsupported-operation]
          kernel_size=1,
          strides=1,
          use_bias=False,

View on GitHub (pinned to e006f5f0d5)

Solutions

1. Use a supported block_fn: 'bottleneck' or 'basic'.
2. Check the block_fn value in the backbone config for typos.

When it happens

Trigger: Thrown at official/vision/modeling/backbones/resnet_unet.py:397 when the library encounters an invalid state.

Common situations: See trigger scenarios.

AI-assisted analysis of tensorflow/models@e006f5f0d5 (2026-08-24). Data as JSON: /api/errors/75ae961f327bc7c4. Report an issue: GitHub.