code: '''
  Train
  Train your nerual network
  Author: Tawn Kramer
  '''
  from __future__ import print_function
  import os
  import sys
  import glob
  import time
  import fnmatch
  import argparse
  import numpy as np
  from PIL import Image
  import keras
  import conf
  import random
  import augment
  import models
  
  
  '''
  matplotlib can be a pain to setup. So handle the case where it is absent. When present,
  use it to generate a plot of training results.
  '''
  try:
      import matplotlib
      # Force matplotlib to not use any Xwindows backend.
      matplotlib.use('Agg')
  
      import matplotlib.pyplot as plt
      do_plot = True
  except:
      do_plot = False
  
  
  def shuffle(samples):
      '''
      randomly mix a list and return a new list
      '''
      ret_arr = []
      len_samples = len(samples)
      while len_samples > 0:
          iSample = random.randrange(0, len_samples)
          ret_arr.append(samples[iSample])
          del samples[iSample]
          len_samples -= 1
      return ret_arr
  
  def parse_img_filepath(filepath):
      basename = os.path.basename(filepath)
  
      #less .jpg
      f = basename[:-4]
      f = f.split('_')
  
      steering = float(f[3])
      throttle = float(f[5])
      
      data = {'steering':steering, 'throttle':throttle }
  
      return data
  
  def generator(samples, batch_size=32, perc_to_augment=0.5):
      '''
      Rather than keep all data in memory, we will make a function that keeps
      it's state and returns just the latest batch required via the yield command.
      
      As we load images, we can optionally augment them in some manner that doesn't
      change their underlying meaning or features. This is a combination of
      brightness, contrast, sharpness, and color PIL image filters applied with random
      settings. Optionally a shadow image may be overlayed with some random rotation and
      opacity.
      We flip each image horizontally and supply it as a another sample with the steering
      negated.
      '''
      num_samples = len(samples)
      shadows = augment.load_shadow_images('./shadows/*.png')    
      
      while 1: # Loop forever so the generator never terminates
          samples = shuffle(samples)
          #divide batch_size in half, because we double each output by flipping image.
          for offset in range(0, num_samples, batch_size):
              batch_samples = samples[offset:offset+batch_size]
              
              images = []
              controls = []
              for fullpath in batch_samples:
                  try:
                      data = parse_img_filepath(fullpath)
                  
                      steering = data["steering"]
                      throttle = data["throttle"]
  
                      try:
                          image = Image.open(fullpath)
                      except:
                          image = None
  
                      if image is None:
                          print('failed to open', fullpath)
                          continue
  
                      #PIL Image as a numpy array
                      image = np.array(image)
  
                      if len(shadows) > 0 and random.uniform(0.0, 1.0) < perc_to_augment:
                          image = augment.augment_image(image, shadows)
  
                      center_angle = steering
                      images.append(image)
                      
                      if conf.num_outputs == 2:
                          controls.append([center_angle, throttle])
                      elif conf.num_outputs == 1:
                          controls.append([center_angle])
                      else:
                          print("expected 1 or 2 ouputs")
  
                  except:
                      print("we threw an exception on:", fullpath)
                      yield [], []
  
  
              # final np array to submit to training
              X_train = np.array(images)
              y_train = np.array(controls)
              yield X_train, y_train
  
  
  def get_files(filemask):
      '''
      use a filemask and search a path recursively for matches
      '''
      path, mask = os.path.split(filemask)
      matches = []
      for root, dirnames, filenames in os.walk(path):
          for filename in fnmatch.filter(filenames, mask):
              matches.append(os.path.join(root, filename))
      return matches
  
  
  def train_test_split(lines, test_perc):
      '''
      split a list into two parts, percentage of test used to seperate
      '''
      train = []
      test = []
  
      for line in lines:
          if random.uniform(0.0, 1.0) < test_perc:
              test.append(line)
          else:
              train.append(line)
  
      return train, test
  
  def make_generators(inputs, limit=None, batch_size=32, aug_perc=0.0):
      '''
      load the job spec from the csv and create some generator for training
      '''
      
      #get the image/steering pairs from the csv files
      lines = get_files(inputs)
      print("found %d files" % len(lines))
  
      if limit is not None:
          lines = lines[:limit]
          print("limiting to %d files" % len(lines))
      
      train_samples, validation_samples = train_test_split(lines, test_perc=0.2)
  
      print("num train/val", len(train_samples), len(validation_samples))
      
      # compile and train the model using the generator function
      train_generator = generator(train_samples, batch_size=batch_size, perc_to_augment=aug_perc)
      validation_generator = generator(validation_samples, batch_size=batch_size, perc_to_augment=0.0)
      
      n_train = len(train_samples)
      n_val = len(validation_samples)
      
      return train_generator, validation_generator, n_train, n_val
  
  
  def go(model_name, epochs=50, inputs='./log/*.jpg', limit=None, aug_mult=1, aug_perc=0.0):
  
      print('working on model', model_name)
  
      '''
      modify config.json to select the model to train.
      '''
      model = models.get_nvidia_model(conf.num_outputs)
  
      '''
      display layer summary and weights info
      '''
      models.show_model_summary(model)
  
      callbacks = [
          keras.callbacks.EarlyStopping(monitor='val_loss', patience=conf.training_patience, verbose=0),
          keras.callbacks.ModelCheckpoint(model_name, monitor='val_loss', save_best_only=True, verbose=0),
      ]
      
      batch_size = conf.training_batch_size
  
  
      #Train on session images
      train_generator, validation_generator, n_train, n_val = make_generators(inputs, limit=limit, batch_size=batch_size, aug_perc=aug_perc)
  
      if n_train == 0:
          print('no training data found')
          return
  
      steps_per_epoch = n_train // batch_size
      validation_steps = n_val // batch_size
  
      print("steps_per_epoch", steps_per_epoch, "validation_steps", validation_steps)
  
      history = model.fit_generator(train_generator, 
          steps_per_epoch = steps_per_epoch,
          validation_data = validation_generator,
          validation_steps = validation_steps,
          epochs=epochs,
          verbose=1,
          callbacks=callbacks)
      
      try:
          if do_plot:
              # summarize history for loss
              plt.plot(history.history['loss'])
              plt.plot(history.history['val_loss'])
              plt.title('model loss')
              plt.ylabel('loss')
              plt.xlabel('epoch')
              plt.legend(['train', 'test'], loc='upper left')
              plt.savefig('loss.png')
      except:
          print("problems with loss graph")
  
  if __name__ == "__main__":
      parser = argparse.ArgumentParser(description='train script')
      parser.add_argument('model', type=str, help='model name')
      parser.add_argument('--epochs', type=int, default=conf.training_default_epochs, help='number of epochs')
      parser.add_argument('--inputs', default='../dataset/log/*.jpg', help='input mask to gather images')
      parser.add_argument('--limit', type=int, default=None, help='max number of images to train with')
      parser.add_argument('--aug_mult', type=int, default=conf.training_default_aug_mult, help='how many more images to augment')
      parser.add_argument('--aug_perc', type=float, default=conf.training_default_aug_percent, help='what percentage of images to augment 0 - 1')
      args = parser.parse_args()
      
      go(args.model, epochs=args.epochs, limit=args.limit, inputs=args.inputs, aug_mult=args.aug_mult, aug_perc=args.aug_perc)
  
  #python train.py mymodel_aug_90_x4_e200 --epochs=200 --aug_mult=4 --aug_perc=0.9
  
apis: matplotlib.pyplot.legend matplotlib.pyplot.savefig matplotlib.pyplot.title matplotlib.pyplot.ylabel matplotlib.use matplotlib.pyplot.plot numpy.array matplotlib.pyplot.xlabel