# How to write a Trial running on NNI?

*Trial receive the hyper-parameter/architecture configure from Tuner, and send intermediate result to Assessor and final result to Tuner.* 

So when user want to write a Trial running on NNI, she/he should:

**1)Have an original Trial could run**,

Trial's code could be any machine learning code that could run in local. Here we use `mnist-keras.py` as example:

```python
import argparse
import logging
import keras
import numpy as np
from keras import backend as K
from keras.datasets import mnist
from keras.layers import Conv2D, Dense, Flatten, MaxPooling2D
from keras.models import Sequential

K.set_image_data_format('channels_last')

H, W = 28, 28
NUM_CLASSES = 10

def create_mnist_model(hyper_params, input_shape=(H, W, 1), num_classes=NUM_CLASSES):
    layers = [
        Conv2D(32, kernel_size=(3, 3), activation='relu', input_shape=input_shape),
        Conv2D(64, (3, 3), activation='relu'),
        MaxPooling2D(pool_size=(2, 2)),
        Flatten(),
        Dense(100, activation='relu'),
        Dense(num_classes, activation='softmax')
    ]

    model = Sequential(layers)

    if hyper_params['optimizer'] == 'Adam':
        optimizer = keras.optimizers.Adam(lr=hyper_params['learning_rate'])
    else:
        optimizer = keras.optimizers.SGD(lr=hyper_params['learning_rate'], momentum=0.9)
    model.compile(loss=keras.losses.categorical_crossentropy, optimizer=optimizer, metrics=['accuracy'])

    return model

def load_mnist_data(args):
    (x_train, y_train), (x_test, y_test) = mnist.load_data()

    x_train = (np.expand_dims(x_train, -1).astype(np.float) / 255.)[:args.num_train]
    x_test = (np.expand_dims(x_test, -1).astype(np.float) / 255.)[:args.num_test]
    y_train = keras.utils.to_categorical(y_train, NUM_CLASSES)[:args.num_train]
    y_test = keras.utils.to_categorical(y_test, NUM_CLASSES)[:args.num_test]

    return x_train, y_train, x_test, y_test

class SendMetrics(keras.callbacks.Callback):
    def on_epoch_end(self, epoch, logs={}):
        pass

def train(args, params):
    x_train, y_train, x_test, y_test = load_mnist_data(args)
    model = create_mnist_model(params)

    model.fit(x_train, y_train, batch_size=args.batch_size, epochs=args.epochs, verbose=1,
        validation_data=(x_test, y_test), callbacks=[SendMetrics()])

    _, acc = model.evaluate(x_test, y_test, verbose=0)

def generate_default_params():
    return {
        'optimizer': 'Adam',
        'learning_rate': 0.001
    }

if __name__ == '__main__':
    PARSER = argparse.ArgumentParser()
    PARSER.add_argument("--batch_size", type=int, default=200, help="batch size", required=False)
    PARSER.add_argument("--epochs", type=int, default=10, help="Train epochs", required=False)
    PARSER.add_argument("--num_train", type=int, default=1000, help="Number of train samples to be used, maximum 60000", required=False)
    PARSER.add_argument("--num_test", type=int, default=1000, help="Number of test samples to be used, maximum 10000", required=False)

    ARGS, UNKNOWN = PARSER.parse_known_args()
    PARAMS = generate_default_params()
    train(ARGS, PARAMS)
```

**2)Get configure from Tuner**

User import `nni` and use `nni.get_next_parameter()` to receive configure. Please noted **10**, **24** and **25** line in the following code.


```python
import argparse
import logging
import keras
import numpy as np
from keras import backend as K
from keras.datasets import mnist
from keras.layers import Conv2D, Dense, Flatten, MaxPooling2D
from keras.models import Sequential

import nni

...

if __name__ == '__main__':
    PARSER = argparse.ArgumentParser()
    PARSER.add_argument("--batch_size", type=int, default=200, help="batch size", required=False)
    PARSER.add_argument("--epochs", type=int, default=10, help="Train epochs", required=False)
    PARSER.add_argument("--num_train", type=int, default=1000, help="Number of train samples to be used, maximum 60000", required=False)
    PARSER.add_argument("--num_test", type=int, default=1000, help="Number of test samples to be used, maximum 10000", required=False)

    ARGS, UNKNOWN = PARSER.parse_known_args()

    PARAMS = generate_default_params()
    RECEIVED_PARAMS = nni.get_next_parameter()
    PARAMS.update(RECEIVED_PARAMS)
    train(ARGS, PARAMS)
```


**3)  Send intermediate result**

Use `nni.report_intermediate_result` to send intermediate result to Assessor. Please noted **5** line in the following code.


```python
...

class SendMetrics(keras.callbacks.Callback):
    def on_epoch_end(self, epoch, logs={}):
        nni.report_intermediate_result(logs)

def train(args, params):
    x_train, y_train, x_test, y_test = load_mnist_data(args)
    model = create_mnist_model(params)

    model.fit(x_train, y_train, batch_size=args.batch_size, epochs=args.epochs, verbose=1,
        validation_data=(x_test, y_test), callbacks=[SendMetrics()])

    _, acc = model.evaluate(x_test, y_test, verbose=0)

...    
```
**4) Send final result**  

Use `nni.report_final_result` to send final result to Tuner. Please noted **15** line in the following code.

```python
...

class SendMetrics(keras.callbacks.Callback):
    def on_epoch_end(self, epoch, logs={}):
        nni.report_intermediate_result(logs)

def train(args, params):
    x_train, y_train, x_test, y_test = load_mnist_data(args)
    model = create_mnist_model(params)

    model.fit(x_train, y_train, batch_size=args.batch_size, epochs=args.epochs, verbose=1,
        validation_data=(x_test, y_test), callbacks=[SendMetrics()])

    _, acc = model.evaluate(x_test, y_test, verbose=0)
    nni.report_final_result(acc)
...    
```

Here is the complete example:


```python
import argparse
import logging

import keras
import numpy as np
from keras import backend as K
from keras.datasets import mnist
from keras.layers import Conv2D, Dense, Flatten, MaxPooling2D
from keras.models import Sequential

import nni

LOG = logging.getLogger('mnist_keras')
K.set_image_data_format('channels_last')

H, W = 28, 28
NUM_CLASSES = 10

def create_mnist_model(hyper_params, input_shape=(H, W, 1), num_classes=NUM_CLASSES):
    '''
    Create simple convolutional model
    '''
    layers = [
        Conv2D(32, kernel_size=(3, 3), activation='relu', input_shape=input_shape),
        Conv2D(64, (3, 3), activation='relu'),
        MaxPooling2D(pool_size=(2, 2)),
        Flatten(),
        Dense(100, activation='relu'),
        Dense(num_classes, activation='softmax')
    ]

    model = Sequential(layers)

    if hyper_params['optimizer'] == 'Adam':
        optimizer = keras.optimizers.Adam(lr=hyper_params['learning_rate'])
    else:
        optimizer = keras.optimizers.SGD(lr=hyper_params['learning_rate'], momentum=0.9)
    model.compile(loss=keras.losses.categorical_crossentropy, optimizer=optimizer, metrics=['accuracy'])

    return model

def load_mnist_data(args):
    '''
    Load MNIST dataset
    '''
    (x_train, y_train), (x_test, y_test) = mnist.load_data()

    x_train = (np.expand_dims(x_train, -1).astype(np.float) / 255.)[:args.num_train]
    x_test = (np.expand_dims(x_test, -1).astype(np.float) / 255.)[:args.num_test]
    y_train = keras.utils.to_categorical(y_train, NUM_CLASSES)[:args.num_train]
    y_test = keras.utils.to_categorical(y_test, NUM_CLASSES)[:args.num_test]

    LOG.debug('x_train shape: %s', (x_train.shape,))
    LOG.debug('x_test shape: %s', (x_test.shape,))

    return x_train, y_train, x_test, y_test

class SendMetrics(keras.callbacks.Callback):
    '''
    Keras callback to send metrics to NNI framework
    '''
    def on_epoch_end(self, epoch, logs={}):
        '''
        Run on end of each epoch
        '''
        LOG.debug(logs)
        nni.report_intermediate_result(logs)

def train(args, params):
    '''
    Train model
    '''
    x_train, y_train, x_test, y_test = load_mnist_data(args)
    model = create_mnist_model(params)

    model.fit(x_train, y_train, batch_size=args.batch_size, epochs=args.epochs, verbose=1,
        validation_data=(x_test, y_test), callbacks=[SendMetrics()])

    _, acc = model.evaluate(x_test, y_test, verbose=0)
    LOG.debug('Final result is: %d', acc)
    nni.report_final_result(acc)

def generate_default_params():
    '''
    Generate default hyper parameters
    '''
    return {
        'optimizer': 'Adam',
        'learning_rate': 0.001
    }

if __name__ == '__main__':
    PARSER = argparse.ArgumentParser()
    PARSER.add_argument("--batch_size", type=int, default=200, help="batch size", required=False)
    PARSER.add_argument("--epochs", type=int, default=10, help="Train epochs", required=False)
    PARSER.add_argument("--num_train", type=int, default=1000, help="Number of train samples to be used, maximum 60000", required=False)
    PARSER.add_argument("--num_test", type=int, default=1000, help="Number of test samples to be used, maximum 10000", required=False)

    ARGS, UNKNOWN = PARSER.parse_known_args()

    try:
        # get parameters from tuner
        RECEIVED_PARAMS = nni.get_next_parameter()
        LOG.debug(RECEIVED_PARAMS)
        PARAMS = generate_default_params()
        PARAMS.update(RECEIVED_PARAMS)
        # train
        train(ARGS, PARAMS)
    except Exception as e:
        LOG.exception(e)
        raise

```
