Course 5 Week 1 Assignment 1 (C5W1A3) Issue Identified in music_inference_model – Incorrect Model Inputs Causing Test Failure

Course Q&A Deep Learning Specialization Sequence Models
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Hi team,

I hope you’re all doing well. I wanted to share an issue I encountered while implementing the music_inference_model function in our sequence‑generation assignment. Even though the model produced the correct number of outputs and shapes (e.g., 50 outputs, each of shape (None, 90)), the grader consistently failed with the message:

“Error in test. The lists contain a different number of elements.”

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That error is not from the grader: it is from the internal tests in the notebook. What it is telling you is not about the shapes of the inputs or outputs: it is telling you that your model does not have the correct number of layers. That comparator test is comparing the output of the summary for your model versus the expected one.

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I added this cell to my version of that assignment to give a more readable form of the output:

print("Generated model:")
for index, a in enumerate(summary(inference_model)):
    print(f"layer {index}: {a}")

Running that in my notebook, which passes the grader, gives this output for the summary:

Generated model:
layer 0: ['InputLayer', [(None, 1, 90)], 0]
layer 1: ['InputLayer', [(None, 64)], 0]
layer 2: ['InputLayer', [(None, 64)], 0]
layer 3: ['LSTM', [(None, 64), (None, 64), (None, 64)], 39680, [(None, 1, 90), (None, 64), (None, 64)], 'tanh']
layer 4: ['Dense', (None, 90), 5850, 'softmax']
layer 5: ['TensorFlowOpLayer', [(None,)], 0]
layer 6: ['TensorFlowOpLayer', [(None, 90)], 0]
layer 7: ['RepeatVector', (None, 1, 90), 0, 1]
layer 8: ['TensorFlowOpLayer', [(None,)], 0]
layer 9: ['TensorFlowOpLayer', [(None, 90)], 0]
layer 10: ['RepeatVector', (None, 1, 90), 0, 1]
layer 11: ['TensorFlowOpLayer', [(None,)], 0]
layer 12: ['TensorFlowOpLayer', [(None, 90)], 0]
layer 13: ['RepeatVector', (None, 1, 90), 0, 1]
layer 14: ['TensorFlowOpLayer', [(None,)], 0]
layer 15: ['TensorFlowOpLayer', [(None, 90)], 0]
layer 16: ['RepeatVector', (None, 1, 90), 0, 1]
layer 17: ['TensorFlowOpLayer', [(None,)], 0]
layer 18: ['TensorFlowOpLayer', [(None, 90)], 0]
layer 19: ['RepeatVector', (None, 1, 90), 0, 1]
layer 20: ['TensorFlowOpLayer', [(None,)], 0]
layer 21: ['TensorFlowOpLayer', [(None, 90)], 0]
layer 22: ['RepeatVector', (None, 1, 90), 0, 1]
layer 23: ['TensorFlowOpLayer', [(None,)], 0]
layer 24: ['TensorFlowOpLayer', [(None, 90)], 0]
layer 25: ['RepeatVector', (None, 1, 90), 0, 1]
layer 26: ['TensorFlowOpLayer', [(None,)], 0]
layer 27: ['TensorFlowOpLayer', [(None, 90)], 0]
layer 28: ['RepeatVector', (None, 1, 90), 0, 1]
layer 29: ['TensorFlowOpLayer', [(None,)], 0]
layer 30: ['TensorFlowOpLayer', [(None, 90)], 0]
layer 31: ['RepeatVector', (None, 1, 90), 0, 1]
layer 32: ['TensorFlowOpLayer', [(None,)], 0]
layer 33: ['TensorFlowOpLayer', [(None, 90)], 0]
layer 34: ['RepeatVector', (None, 1, 90), 0, 1]
layer 35: ['TensorFlowOpLayer', [(None,)], 0]
layer 36: ['TensorFlowOpLayer', [(None, 90)], 0]
layer 37: ['RepeatVector', (None, 1, 90), 0, 1]
layer 38: ['TensorFlowOpLayer', [(None,)], 0]
layer 39: ['TensorFlowOpLayer', [(None, 90)], 0]
layer 40: ['RepeatVector', (None, 1, 90), 0, 1]
layer 41: ['TensorFlowOpLayer', [(None,)], 0]
layer 42: ['TensorFlowOpLayer', [(None, 90)], 0]
layer 43: ['RepeatVector', (None, 1, 90), 0, 1]
layer 44: ['TensorFlowOpLayer', [(None,)], 0]
layer 45: ['TensorFlowOpLayer', [(None, 90)], 0]
layer 46: ['RepeatVector', (None, 1, 90), 0, 1]
layer 47: ['TensorFlowOpLayer', [(None,)], 0]
layer 48: ['TensorFlowOpLayer', [(None, 90)], 0]
layer 49: ['RepeatVector', (None, 1, 90), 0, 1]
layer 50: ['TensorFlowOpLayer', [(None,)], 0]
layer 51: ['TensorFlowOpLayer', [(None, 90)], 0]
layer 52: ['RepeatVector', (None, 1, 90), 0, 1]
layer 53: ['TensorFlowOpLayer', [(None,)], 0]
layer 54: ['TensorFlowOpLayer', [(None, 90)], 0]
layer 55: ['RepeatVector', (None, 1, 90), 0, 1]
layer 56: ['TensorFlowOpLayer', [(None,)], 0]
layer 57: ['TensorFlowOpLayer', [(None, 90)], 0]
layer 58: ['RepeatVector', (None, 1, 90), 0, 1]
layer 59: ['TensorFlowOpLayer', [(None,)], 0]
layer 60: ['TensorFlowOpLayer', [(None, 90)], 0]
layer 61: ['RepeatVector', (None, 1, 90), 0, 1]
layer 62: ['TensorFlowOpLayer', [(None,)], 0]
layer 63: ['TensorFlowOpLayer', [(None, 90)], 0]
layer 64: ['RepeatVector', (None, 1, 90), 0, 1]
layer 65: ['TensorFlowOpLayer', [(None,)], 0]
layer 66: ['TensorFlowOpLayer', [(None, 90)], 0]
layer 67: ['RepeatVector', (None, 1, 90), 0, 1]
layer 68: ['TensorFlowOpLayer', [(None,)], 0]
layer 69: ['TensorFlowOpLayer', [(None, 90)], 0]
layer 70: ['RepeatVector', (None, 1, 90), 0, 1]
layer 71: ['TensorFlowOpLayer', [(None,)], 0]
layer 72: ['TensorFlowOpLayer', [(None, 90)], 0]
layer 73: ['RepeatVector', (None, 1, 90), 0, 1]
layer 74: ['TensorFlowOpLayer', [(None,)], 0]
layer 75: ['TensorFlowOpLayer', [(None, 90)], 0]
layer 76: ['RepeatVector', (None, 1, 90), 0, 1]
layer 77: ['TensorFlowOpLayer', [(None,)], 0]
layer 78: ['TensorFlowOpLayer', [(None, 90)], 0]
layer 79: ['RepeatVector', (None, 1, 90), 0, 1]
layer 80: ['TensorFlowOpLayer', [(None,)], 0]
layer 81: ['TensorFlowOpLayer', [(None, 90)], 0]
layer 82: ['RepeatVector', (None, 1, 90), 0, 1]
layer 83: ['TensorFlowOpLayer', [(None,)], 0]
layer 84: ['TensorFlowOpLayer', [(None, 90)], 0]
layer 85: ['RepeatVector', (None, 1, 90), 0, 1]
layer 86: ['TensorFlowOpLayer', [(None,)], 0]
layer 87: ['TensorFlowOpLayer', [(None, 90)], 0]
layer 88: ['RepeatVector', (None, 1, 90), 0, 1]
layer 89: ['TensorFlowOpLayer', [(None,)], 0]
layer 90: ['TensorFlowOpLayer', [(None, 90)], 0]
layer 91: ['RepeatVector', (None, 1, 90), 0, 1]
layer 92: ['TensorFlowOpLayer', [(None,)], 0]
layer 93: ['TensorFlowOpLayer', [(None, 90)], 0]
layer 94: ['RepeatVector', (None, 1, 90), 0, 1]
layer 95: ['TensorFlowOpLayer', [(None,)], 0]
layer 96: ['TensorFlowOpLayer', [(None, 90)], 0]
layer 97: ['RepeatVector', (None, 1, 90), 0, 1]
layer 98: ['TensorFlowOpLayer', [(None,)], 0]
layer 99: ['TensorFlowOpLayer', [(None, 90)], 0]
layer 100: ['RepeatVector', (None, 1, 90), 0, 1]
layer 101: ['TensorFlowOpLayer', [(None,)], 0]
layer 102: ['TensorFlowOpLayer', [(None, 90)], 0]
layer 103: ['RepeatVector', (None, 1, 90), 0, 1]
layer 104: ['TensorFlowOpLayer', [(None,)], 0]
layer 105: ['TensorFlowOpLayer', [(None, 90)], 0]
layer 106: ['RepeatVector', (None, 1, 90), 0, 1]
layer 107: ['TensorFlowOpLayer', [(None,)], 0]
layer 108: ['TensorFlowOpLayer', [(None, 90)], 0]
layer 109: ['RepeatVector', (None, 1, 90), 0, 1]
layer 110: ['TensorFlowOpLayer', [(None,)], 0]
layer 111: ['TensorFlowOpLayer', [(None, 90)], 0]
layer 112: ['RepeatVector', (None, 1, 90), 0, 1]
layer 113: ['TensorFlowOpLayer', [(None,)], 0]
layer 114: ['TensorFlowOpLayer', [(None, 90)], 0]
layer 115: ['RepeatVector', (None, 1, 90), 0, 1]
layer 116: ['TensorFlowOpLayer', [(None,)], 0]
layer 117: ['TensorFlowOpLayer', [(None, 90)], 0]
layer 118: ['RepeatVector', (None, 1, 90), 0, 1]
layer 119: ['TensorFlowOpLayer', [(None,)], 0]
layer 120: ['TensorFlowOpLayer', [(None, 90)], 0]
layer 121: ['RepeatVector', (None, 1, 90), 0, 1]
layer 122: ['TensorFlowOpLayer', [(None,)], 0]
layer 123: ['TensorFlowOpLayer', [(None, 90)], 0]
layer 124: ['RepeatVector', (None, 1, 90), 0, 1]
layer 125: ['TensorFlowOpLayer', [(None,)], 0]
layer 126: ['TensorFlowOpLayer', [(None, 90)], 0]
layer 127: ['RepeatVector', (None, 1, 90), 0, 1]
layer 128: ['TensorFlowOpLayer', [(None,)], 0]
layer 129: ['TensorFlowOpLayer', [(None, 90)], 0]
layer 130: ['RepeatVector', (None, 1, 90), 0, 1]
layer 131: ['TensorFlowOpLayer', [(None,)], 0]
layer 132: ['TensorFlowOpLayer', [(None, 90)], 0]
layer 133: ['RepeatVector', (None, 1, 90), 0, 1]
layer 134: ['TensorFlowOpLayer', [(None,)], 0]
layer 135: ['TensorFlowOpLayer', [(None, 90)], 0]
layer 136: ['RepeatVector', (None, 1, 90), 0, 1]
layer 137: ['TensorFlowOpLayer', [(None,)], 0]
layer 138: ['TensorFlowOpLayer', [(None, 90)], 0]
layer 139: ['RepeatVector', (None, 1, 90), 0, 1]
layer 140: ['TensorFlowOpLayer', [(None,)], 0]
layer 141: ['TensorFlowOpLayer', [(None, 90)], 0]
layer 142: ['RepeatVector', (None, 1, 90), 0, 1]
layer 143: ['TensorFlowOpLayer', [(None,)], 0]
layer 144: ['TensorFlowOpLayer', [(None, 90)], 0]
layer 145: ['RepeatVector', (None, 1, 90), 0, 1]
layer 146: ['TensorFlowOpLayer', [(None,)], 0]
layer 147: ['TensorFlowOpLayer', [(None, 90)], 0]
layer 148: ['RepeatVector', (None, 1, 90), 0, 1]
layer 149: ['TensorFlowOpLayer', [(None,)], 0]
layer 150: ['TensorFlowOpLayer', [(None, 90)], 0]
layer 151: ['RepeatVector', (None, 1, 90), 0, 1]

Notice that there should be a total of 152 layers in the model. What do you see when you run that in your notebook? If it is a different number, then you can compare the two lists to get an idea of where your problem is.