Remove support for IPython<4.

We require Python 3.8, which is itself not compatible with IPython<7.3
due to IPython issue 11590.

As a side benefit, this avoids slightly confusing error messages in
backend_nbagg when IPython is installed but not ipykernel (we now always
depend on ipykernel for backend_nbagg, and ipykernel itself depends on
IPython but not the other way round).

Author: anntzer

lib/matplotlib/backends/backend_nbagg.py

@@ -9,13 +9,8 @@
 import pathlib
 import uuid
 
+from ipykernel.comm import Comm
 from IPython.display import display, Javascript, HTML
-try:
-    # Jupyter/IPython 4.x or later
-    from ipykernel.comm import Comm
-except ImportError:
-    # Jupyter/IPython 3.x or earlier
-    from IPython.kernel.comm import Comm
 
 from matplotlib import is_interactive
 from matplotlib._pylab_helpers import Gcf
@@ -44,18 +39,13 @@ def connection_info():
     return '\n'.join(result)
 
 
-# Note: Version 3.2 and 4.x icons
-# https://fontawesome.com/v3.2/icons/
-# https://fontawesome.com/v4.7/icons/
-# the `fa fa-xxx` part targets font-awesome 4, (IPython 3.x)
-# the icon-xxx targets font awesome 3.21 (IPython 2.x)
-_FONT_AWESOME_CLASSES = {
-    'home': 'fa fa-home icon-home',
-    'back': 'fa fa-arrow-left icon-arrow-left',
-    'forward': 'fa fa-arrow-right icon-arrow-right',
-    'zoom_to_rect': 'fa fa-square-o icon-check-empty',
-    'move': 'fa fa-arrows icon-move',
-    'download': 'fa fa-floppy-o icon-save',
+_FONT_AWESOME_CLASSES = {  # font-awesome 4 names
+    'home': 'fa fa-home',
+    'back': 'fa fa-arrow-left',
+    'forward': 'fa fa-arrow-right',
+    'zoom_to_rect': 'fa fa-square-o',
+    'move': 'fa fa-arrows',
+    'download': 'fa fa-floppy-o',
     None: None
 }
 

lib/matplotlib/pyplot.py

@@ -140,10 +140,7 @@ def post_execute():
         if matplotlib.is_interactive():
             draw_all()
 
-    try:  # IPython >= 2
-        ip.events.register("post_execute", post_execute)
-    except AttributeError:  # IPython 1.x
-        ip.register_post_execute(post_execute)
+    ip.events.register("post_execute", post_execute)
     _IP_REGISTERED = post_execute
     _INSTALL_FIG_OBSERVER = False
 
@@ -160,26 +157,16 @@ def uninstall_repl_displayhook():
 
     .. warning::
 
-       Need IPython >= 2 for this to work.  For IPython < 2 will raise a
-       ``NotImplementedError``
-
-    .. warning::
-
-       If you are using vanilla python and have installed another
-       display hook, this will reset ``sys.displayhook`` to what ever
-       function was there when Matplotlib installed its displayhook,
-       possibly discarding your changes.
+       If you are using vanilla python and have installed another display hook,
+       this will reset `sys.displayhook` to what ever function was there when
+       Matplotlib installed its displayhook, possibly discarding your changes.
     """
     global _IP_REGISTERED
     global _INSTALL_FIG_OBSERVER
     if _IP_REGISTERED:
         from IPython import get_ipython
         ip = get_ipython()
-        try:
-            ip.events.unregister('post_execute', _IP_REGISTERED)
-        except AttributeError as err:
-            raise NotImplementedError("Can not unregister events "
-                                      "in IPython < 2.0") from err
+        ip.events.unregister('post_execute', _IP_REGISTERED)
         _IP_REGISTERED = None
 
     if _INSTALL_FIG_OBSERVER: