theano_backend.py 文件源码

def placeholder(shape=None, ndim=None, dtype=None, sparse=False, name=None):
    """Instantiate an input data placeholder variable.
    """
    if dtype is None:
        dtype = floatx()
    if shape is None and ndim is None:
        raise ValueError('Specify either a shape or ndim value.')
    if shape is not None:
        ndim = len(shape)
    else:
        shape = tuple([None for _ in range(ndim)])

    name = _prepare_name(name, 'placeholder')
    broadcast = (False,) * ndim
    if sparse:
        _assert_sparse_module()
        x = th_sparse_module.csr_matrix(name=name, dtype=dtype)
    else:
        x = T.TensorType(dtype, broadcast)(name)
    x._keras_shape = shape
    x._uses_learning_phase = False
    return x