AttributeError: 'Tensor' object has no attribute 'shape' when uses tensor.shape(my keras version==1.2.0)

I have the following code which uses keras and it raises:

AttributeError: 'Tensor' object has no attribute 'shape'

The code:

def call( self, tx_and_ty, mask = None ) :
    tx, ty = tx_and_ty
    n_samples, n_chs, n_rows, n_cols = tx.get_shape()
    n_pixs = n_rows * n_cols
    txf = tx.reshape( ( n_samples, n_chs, n_pixs ) ).dimshuffle( 0, 2, 1 ) # ( n_samples, n_pixs, n_chs )
    tyf = ty.reshape( ( n_samples, n_chs, n_pixs ) ) / n_chs # ( n_samples, n_chs, n_pixs )
    res = tt.batched_dot( txf, tyf ) # ( n_samples, n_pixs, n_pixs )
    resf = res.flatten( 2 ).dimshuffle( 1, 0 )
    resm = resf[ self.midx ].dimshuffle( 1, 0 ).reshape( [n_samples, n_pixs, n_rows, n_cols] )
    return tt.cast( resm, 'float32' )

Could anyone please tell me what I am missing?