title: Tensorflow cannot initialize tf.Variable for dynamic batch size
body: <p>I tried creating a tf.Variable with a dynamic shape. The following outlines the problem.</p>
  
  <p>Doing this works. </p>
  
  <pre><code>init_bias = tf.random_uniform(shape=[self.config.hidden_layer_size, tf.shape(self.question_inputs)[0]])
  </code></pre>
  
  <p>However, when i try to do this:</p>
  
  <pre><code>init_bias = tf.Variable(init_bias)
  </code></pre>
  
  <p>It throws the error ValueError: initial_value must have a shape specified: Tensor("random_uniform:0", shape=(?, ?), dtype=float32)</p>
  
  <p>Just come context (question input is a placeholder which dynamic batch ):</p>
  
  <pre><code>self.question_inputs = tf.placeholder(tf.int32, shape=[None, self.config.qmax])
  </code></pre>
  
  <p>It seems like putting a dynamic value into random uniform gives shape=(?,?) which gives an error with tf.Variable. </p>
  
  <p>Thanks and appreciate any help!</p>