keras的backend 设置 tensorflow,theano操作

C:\Users\Administrator>python
Python 2.7.12 |Anaconda 4.2.0 (64-bit)| (default, Jun 29 2016, 11:07:13) [MSC v.1500 64 bit (AMD64)] on win32
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>>> import keras
Using TensorFlow backend.
Traceback (most recent call last):
 File "<stdin>", line 1, in <module>
 File "C:\Anaconda2\lib\site-packages\keras\__init__.py", line 2, in <module>
 from . import backend
 File "C:\Anaconda2\lib\site-packages\keras\backend\__init__.py", line 68, in <module>
 from .tensorflow_backend import *
 File "C:\Anaconda2\lib\site-packages\keras\backend\tensorflow_backend.py", line 1, in <module>
 import tensorflow as tf
ImportError: No module named tensorflow
>>> import keras
Using Theano backend.
WARNING (theano.configdefaults): g++ not detected ! Theano will be unable to execute optimized C-implementations (for both CPU and GPU) and will default to Python implementations. Performance will be severely degraded. To remove this warning, set Theano flags cxx to an empty string.

# Default backend: TensorFlow.
#_BACKEND = 'tensorflow'
_BACKEND = 'theano'

C:\Users\Administrator\.keras\keras.json
{
"image_dim_ordering":"tf",
"epsilon":1e-07,
"floatx":"float32",
"backend":"tensorflow"
}

{
 "image_dim_ordering": "tf", 
 "epsilon": 1e-07, 
 "floatx": "float32", 
 "backend": "theano"
}

// 一般在文件的180行左右，修改为如下
...
else:
    if _SESSION is None:
      if not os.environ.get('OMP_NUM_THREADS'):
        config = tf.ConfigProto(allow_soft_placement=True)
        config.gpu_options.allow_growth=True
        config.gpu_options.per_process_gpu_memory_fraction=0.9
      else:
        num_thread = int(os.environ.get('OMP_NUM_THREADS'))
        config = tf.ConfigProto(intra_op_parallelism_threads=num_thread,
                    allow_soft_placement=True)
        config.gpu_options.allow_growth=True
        config.gpu_options.per_process_gpu_memory_fraction=0.9
      _SESSION = tf.Session(config=config)
    session = _SESSION
  ...