keras中的fit_generator和fit函數均返回History對象，那么History怎么用呢？事實上History對象已經記錄了運行輸出。在了解之前，我們甚至自己定義回調函數記錄損失和準確率等。

相關keras源碼位于網址：

class History(Callback):

"""Callback that records events into a `History` object.

This callback is automatically applied to

every Keras model. The `History` object

gets returned by the `fit` method of models.

"""

def on_train_begin(self, logs=None):

self.epoch = []

self.history = {}

def on_epoch_end(self, epoch, logs=None):

logs = logs or {}

self.epoch.append(epoch)

for k, v in logs.items():

self.history.setdefault(k, []).append(v)

可以看出History類對象包含兩個屬性，分別為epoch和history，epoch為訓練輪數。

根據compile參數metrics，history包含不同的內容。比如，當某一次metrics=['accuracy']時，運行如下部分代碼我們可以看出，history字典類型，包含val_loss,val_acc,loss,acc四個key值。

####省略若干

history = model.fit_generator(

mp.train_flow,

steps_per_epoch=32,

epochs=3,

validation_data=mp.test_flow,

validation_steps=32)

print(history.history)

print(history.epoch)

print(history.history['val_loss'])

{‘val_loss': [0.4231100323200226, 0.3713115310668945, 0.3836631367206573], ‘val_acc': [0.815, 0.84, 0.83], ‘loss': [0.8348453622311354, 0.5010451343324449, 0.4296100065112114], ‘acc': [0.630859375, 0.7509920634920635, 0.783203125]}

[0, 1, 2]

[0.4231100323200226, 0.3713115310668945, 0.3836631367206573]

補充知識：在ipython中使用%history快速查找歷史命令

1、輸出所有歷史記錄，且帶有序號

%history -n

150: %cpaste

151: %cpaste

152: print(r">>>>>>>>>")

153: print(r'>>>>>>>>>')

154: print(r'>>>>>>>>>

155: print(r'>')

156: print(r'>>')

157: print(r'>>>')

...

2、按序號，查找某些序號區間的歷史紀錄

%history -n 168-170 178 185-190

168: planets

169:

for method, group in planets.groupby('method'):

print(f'{method:30s} method={group}')

170:

for method, group in planets.groupby('method'):

print(f'{method:30s} method={group.shape}')

178: %history?

185: %history -u

186: %history -n -u

187: ?%history

188: %history -g method

189: %history -g method print

190: %history -g for method,

3、模糊查找

%history -g print*metho*

120:

for method, group in planets.groupby('method'):

print(f"{method:30s} shape={groupe.shape}")

121:

for method, group in planets.groupby('method'):

print(f"{method:30s} shape={group.shape}")

169:

for method, group in planets.groupby('method'):

print(f'{method:30s} method={group}')

170:

for method, group in planets.groupby('method'):

print(f'{method:30s} method={group.shape}')

182:

for method, group in planets.groupby('method'):

print(f"{method:30s shape=group.shape}")

198: %history -g print*metho*

以上這篇keras中的History對象用法就是小編分享給大家的全部內容了，希望能給大家一個參考，也希望大家多多支持腳本之家。

總結

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