@@ -1429,27 +1429,37 @@ def bands(sys, args=(), momenta=65, file=None, show=True, dpi=None,

         Either a number of sampling points on the interval [-pi, pi], or an

         array of points at which the band structure has to be evaluated.

     file : string or file object or `None`

-        The output file.  If `None`, output will be shown instead.

+        The output file.  If `None`, output will be shown instead. If plotly is

+        selected as the backend, the filename has to end with a html extension.

     show : bool

-        Whether ``matplotlib.pyplot.show()`` is to be called, and the output is

-        to be shown immediately.  Defaults to `True`.

+        For matplotlib backend, whether ``matplotlib.pyplot.show()`` is to be

+        called, and the output is to be shown immediately.

+        For the plotly backend, a call to ``iplot(fig)`` is made if

+        show is True.

+        Defaults to `True` for both backends.

     dpi : float

         Number of pixels per inch.  If not set the ``matplotlib`` default is

         used.

+        Only for matplotlib backend. If the plotly backend is selected and

+        this argument is not None, then a RuntimeError will be triggered.

     fig_size : tuple

         Figure size `(width, height)` in inches.  If not set, the default

         ``matplotlib`` value is used.

+        Only for matplotlib backend. If the plotly backend is selected and

+        this argument is not None, then a RuntimeError will be triggered.

     ax : ``matplotlib.axes.Axes`` instance or `None`

         If `ax` is not `None`, no new figure is created, but the plot is done

         within the existing Axes `ax`. in this case, `file`, `show`, `dpi`

         and `fig_size` are ignored.

+        Only for matplotlib backend. If the plotly backend is selected and

+        this argument is not None, then a RuntimeError will be triggered.

     params : dict, optional

         Dictionary of parameter names and their values. Mutually exclusive

         with 'args'.

     Returns

     -------

-    fig : matplotlib figure

+    fig : matplotlib figure or plotly Figure object

         A figure with the output if `ax` is not set, else None.

     Notes

@@ -1457,11 +1467,20 @@ def bands(sys, args=(), momenta=65, file=None, show=True, dpi=None,

     See `~kwant.physics.Bands` for the calculation of dispersion without plotting.

     """

-    if not _p.mpl_available:

+    if not _p.mpl_available and (get_backend() == _p.Backends.matplotlib):

         raise RuntimeError("matplotlib was not found, but is required "

-                           "for bands()")

+                           "for bands() by the selected backend")

+

+    if not _p.plotly_available and (get_backend() == _p.Backends.plotly):

+        raise RuntimeError("plotly was not found, but is required "

+                           "for bands() by the selected backend")

     syst = sys  # for naming consistency inside function bodies

+

+    if get_backend() == _p.Backends.plotly:

+        _check_incompatible_args_plotly(dpi, fig_size, ax)

+

+

     _common.ensure_isinstance(syst, (system.InfiniteSystem, system.InfiniteVectorizedSystem))

     momenta = np.array(momenta)