__it__() 和__iter__()是一个吗
时间: 2023-07-31 14:12:01 浏览: 34
不,`__iter__()`和`__next__()`是用于定义迭代器的特殊方法,而`__str__()`是用于返回对象的字符串表示的特殊方法。
- `__iter__()`方法用于返回一个迭代器对象,该迭代器对象必须实现`__next__()`方法。
- `__next__()`方法用于返回迭代器的下一个元素,并且在迭代完成后触发`StopIteration`异常。
这两个方法通常一起使用,允许我们在自定义类中实现可迭代行为。而`__str__()`方法是用于返回对象的字符串表示,通常用于对象的打印或字符串拼接操作。
相关问题
def evaluate_accuracy(net, data_iter):
This function computes the accuracy of a neural network model on a given dataset. Here is a possible implementation:
```
def evaluate_accuracy(net, data_iter):
acc_sum, n = 0.0, 0
for X, y in data_iter:
y_hat = net(X)
acc_sum += (y_hat.argmax(axis=1) == y).sum().item()
n += y.size()[0]
return acc_sum / n
```
The function takes two arguments:
- `net`: the neural network model to evaluate.
- `data_iter`: an iterator that generates batches of input data and labels.
The function iterates over the batches in `data_iter`, computes the predicted labels for each batch using the `net` model, and compares these predictions to the true labels to compute the number of correct predictions. It then returns the accuracy, which is the fraction of correct predictions over the total number of examples.
Note that `net(X)` assumes that the model has a `forward` method that takes input data `X` and returns the predicted outputs. Also, `y_hat.argmax(axis=1)` computes the predicted label for each example in the batch by selecting the index with the highest score along the second axis (i.e., the class dimension), and `(y_hat.argmax(axis=1) == y).sum().item()` computes the number of correct predictions in the batch. Finally, `y.size()[0]` computes the number of examples in the batch.
unordered_map的.end函数
unordered_map的.end函数用于返回一个指向unordered_map容器中最后一个元素之后位置的迭代器。它不指向任何有效元素,常用于表示容器的结束位置。
以下是unordered_map的.end函数的使用示例:
```cpp
#include <iostream>
#include <unordered_map>
int main() {
std::unordered_map<int, std::string> myMap = {{1, "apple"}, {2, "banana"}, {3, "orange"}};
// 使用.end函数获取unordered_map的结束位置迭代器
auto it = myMap.end();
// 遍历unordered_map并输出所有键值对
for (auto iter = myMap.begin(); iter != it; ++iter) {
std::cout << "Key: " << iter->first << ", Value: " << iter->second << std::endl;
}
return 0;
}
```
输出结果:
```
Key: 1, Value: apple
Key: 2, Value: banana
Key: 3, Value: orange
```