[Solved] MindSpore Error: “RuntimeError: Unable to data from Generator..”

1 Error description

1.1 System Environment

ardware Environment(Ascend/GPU/CPU): CPU
Software Environment:
– MindSpore version (source or binary): 1.6.0
– Python version (eg, Python 3.7.5): 3.7.6
– OS platform and distribution (eg, Linux Ubuntu 16.04): Ubuntu 4.15.0-74-generic
– GCC/Compiler version (if compiled from source):

1.2 Basic information

1.2.1 Script

This case uses a custom iterable data set for training. During the training process, the first epoch data is iterated normally, and the second epoch will report an error. The custom data code is as follows:

import numpy as np
import mindspore.dataset as ds
from tqdm import tqdm

class IterDatasetGenerator:
    def __init__(self, datax, datay, classes_per_it, num_samples, iterations):
        self.__iterations = iterations
        self.__data = datax
        self.__labels = datay
        self.__iter = 0
        self.classes_per_it = classes_per_it
        self.sample_per_class = num_samples
        self.classes, self.counts = np.unique(self.__labels, return_counts=True)
        self.idxs = range(len(self.__labels))
        self.indexes = np.empty((len(self.classes), max(self.counts)), dtype=int) * np.nan
        self.numel_per_class = np.zeros_like(self.classes)
        for idx, label in tqdm(enumerate(self.__labels)):
            label_idx = np.argwhere(self.classes == label).item()
            self.indexes[label_idx, np.where(np.isnan(self.indexes[label_idx]))[0][0]] = idx
            self.numel_per_class[label_idx] = int(self.numel_per_class[label_idx]) + 1

    def __next__(self):
        spc = self.sample_per_class
        cpi = self.classes_per_it

        if self.__iter >= self.__iterations:
            raise StopIteration
            batch_size = spc * cpi
            batch = np.random.randint(low=batch_size, high=10 * batch_size, size=(batch_size), dtype=np.int64)
            c_idxs = np.random.permutation(len(self.classes))[:cpi]
            for i, c in enumerate(self.classes[c_idxs]):
                index = i*spc
                ci = [c_i for c_i in range(len(self.classes)) if self.classes[c_i] == c][0]
                label_idx = list(range(len(self.classes)))[ci]
                sample_idxs = np.random.permutation(int(self.numel_per_class[label_idx]))[:spc]
                ind = 0
                for i in sample_idxs:
                    batch[index+ind] = self.indexes[label_idx]
                    ind = ind + 1
            batch = batch[np.random.permutation(len(batch))]
            data_x = []
            data_y = []
            for b in batch:
            self.__iter += 1
            item = (data_x, data_y)
            return item

    def __iter__(self):
        return self

    def __len__(self):
        return self.__iterations

data1 = np.random.sample((500,2))
data2 = np.random.sample((500,1))
dataset_generator  = IterDatasetGenerator(data1,data2,5,10,10)
dataset = ds.GeneratorDataset(dataset_generator,["data","label"],shuffle=False)
for epoch in range(epochs):
    for data in dataset.create_dict_iterator():

1.2.2 Error reporting

Error message: RuntimeError: Exception thrown from PyFunc. Unable to fetch data from GeneratorDataset, try iterate the source function of GeneratorDataset or check value of num_epochs when create iterator.

2 Reason analysis

In the process of each data iteration, self.__iter will accumulate. When the second epoch is prefetched, self.__iter has accumulated to the value of the set iterations, resulting in self.__iter >= self.__iterations, and the loop ends.

3 Solutions

Add the clearing operation to def iter(self): and set self.__iter = 0.
The execution is successful at this time, and the output is as follows:

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