Python: Fix missing import with a monkey patch

June 1, 2023

I am trying to monkey patch a missing import. The old_invoke() still does not get the import.
In case it is relevant, MyClass is a gdb.Command.

(gdb) pi
>>> import mymodule
>>> old_invoke = mymodule.MyClass.invoke
>>> def new_invoke(self, *k, **kw):
...   print("New invoke")
...   import getopt
...   old_invoke(self, *k, **kw)
...
>>> mymodule.MyClass.invoke = new_invoke
>>>
(gdb) my_gdb_command
New invoke
Python Exception <class 'NameError'> name 'getopt' is not defined:
Error occurred in Python: name 'getopt' is not defined

Also, in case it is relevant, the initial files and sourcing looks something like this:

mymodule.py:

import gdb
class MyClass(gdb.Command):
   ...

   def invoke(self, arg, from_tty):
      options, remainder = getopt.getopt(args, 'p:s:t:o:')
      ...

MyClass()

myothermodule.py:

import mymodule
...

Sourcing the above

(gdb) source myothermodule.py

>Solution :

old_invoke is trying to reference mymodule‘s getopt, which doesn’t exist. You need:

>>> import mymodule
>>> old_invoke = mymodule.MyClass.invoke
>>> def new_invoke(self, *k, **kw):
...   print("New invoke")
...   import getopt
...   
...   # here
...   mymodule.getopt = getopt
...   
...   old_invoke(self, *k, **kw)
...
>>> mymodule.MyClass.invoke = new_invoke

But, realistically, you should just have an import getopt in mymodule:

# mymodule.py
import getopt
...

Then your function is simply:

>>> import mymodule
>>> old_invoke = mymodule.MyClass.invoke
>>> def new_invoke(self, *k, **kw):
...   print("New invoke")
...   old_invoke(self, *k, **kw)
...
>>> mymodule.MyClass.invoke = new_invoke