Custom lazy magics do not show help (?) until they are imported
Author: krassowskiCreated Sep 2, 2026Updated Sep 9, 2026
Prior to 9.17.0 it did not work at all. Since 9.17.0 it sometimes works on the second attempt (depending on the order of registration):
import sys, types
from IPython.core.interactiveshell import InteractiveShell
from IPython.core.magic import Magics, cell_magic, line_magic, magics_class
@magics_class
class LineHalf(Magics):
@line_magic
def dual(self, line):
"""The line half of %dual."""
@magics_class
class CellHalf(Magics):
@cell_magic
def dual(self, line, cell):
"""The cell half of %%dual."""
sys.modules["provider"] = provider = types.ModuleType("provider")
provider.LineHalf, provider.CellHalf = LineHalf, CellHalf
ip = InteractiveShell()
ip.magics_manager.register_lazy("dual", "provider:LineHalf", "line")
ip.magics_manager.register_lazy("dual", "provider:CellHalf", "cell")
ip.run_cell("%%dual?") # does not work "Object `%%dual` not found."
ip.run_cell("%%dual?") # works, shows "Docstring: The cell half of %%dual."If we swap registration order neither works:
import sys, types
from IPython.core.interactiveshell import InteractiveShell
from IPython.core.magic import Magics, cell_magic, line_magic, magics_class
@magics_class
class LineHalf(Magics):
@line_magic
def dual(self, line):
"""The line half of %dual."""
@magics_class
class CellHalf(Magics):
@cell_magic
def dual(self, line, cell):
"""The cell half of %%dual."""
sys.modules["provider"] = provider = types.ModuleType("provider")
provider.LineHalf, provider.CellHalf = LineHalf, CellHalf
ip = InteractiveShell()
ip.magics_manager.register_lazy("dual", "provider:CellHalf", "cell")
ip.magics_manager.register_lazy("dual", "provider:LineHalf", "line")
ip.run_cell("%%dual?") # does not work "Object `%%dual` not found."
ip.run_cell("%%dual?") # does not work "Object `%%dual` not found."Also, there are issues when overwriting built-in dual magic with say only a line magic:
import sys, types
from IPython.core.interactiveshell import InteractiveShell
from IPython.core.magic import Magics, line_magic, magics_class
@magics_class
class MyMagics(Magics):
@line_magic
def time(self, line):
"""My own %time."""
sys.modules["provider"] = provider = types.ModuleType("provider")
provider.MyMagics = MyMagics
ip = InteractiveShell()
ip.magics_manager.register_lazy("time", "provider:MyMagics")
ip.run_cell("time?") # my own %time
ip.run_cell("%%time?") # expected: IPython's %%time docs
ip.run_cell("%%time\npass") # expected: a wall time reportSource: ipython/ipython