use tf.get_collection

I have also changed the name of the scopes since 'D' and 'D_Pre' where not going to work with tf.get_collection.

gan.py

@@ -138,7 +138,7 @@ def _create_model(self):
 
         # This defines the generator network - it takes samples from a noise
         # distribution as input, and passes them through an MLP.
-        with tf.variable_scope('G'):
+        with tf.variable_scope('Gen'):
             self.z = tf.placeholder(tf.float32, shape=(self.batch_size, 1))
             self.G = generator(self.z, self.mlp_hidden_size)
 
@@ -147,7 +147,7 @@ def _create_model(self):
         #
         # Here we create two copies of the discriminator network (that share parameters),
         # as you cannot use the same network with different inputs in TensorFlow.
-        with tf.variable_scope('D') as scope:
+        with tf.variable_scope('Disc') as scope:
             self.x = tf.placeholder(tf.float32, shape=(self.batch_size, 1))
             self.D1 = discriminator(self.x, self.mlp_hidden_size, self.minibatch)
             scope.reuse_variables()
@@ -158,10 +158,9 @@ def _create_model(self):
         self.loss_d = tf.reduce_mean(-tf.log(self.D1) - tf.log(1 - self.D2))
         self.loss_g = tf.reduce_mean(-tf.log(self.D2))
 
-        vars = tf.trainable_variables()
-        self.d_pre_params = [v for v in vars if v.name.startswith('D_pre/')]
-        self.d_params = [v for v in vars if v.name.startswith('D/')]
-        self.g_params = [v for v in vars if v.name.startswith('G/')]
+        self.d_pre_params = tf.get_collection(tf.GraphKeys.TRAINABLE_VARIABLES, scope='D_pre')
+        self.d_params = tf.get_collection(tf.GraphKeys.TRAINABLE_VARIABLES, scope='Disc')
+        self.g_params = tf.get_collection(tf.GraphKeys.TRAINABLE_VARIABLES, scope='Gen')
 
         self.opt_d = optimizer(self.loss_d, self.d_params, self.learning_rate)
         self.opt_g = optimizer(self.loss_g, self.g_params, self.learning_rate)