Method injecting not working

Question

I am trying to inject my method instead of another method but it works only with methods with small count of arguments.

My injector:

def inject(target_function, new_function):
     @wraps(target_function)
     def _inject(*args, **kwargs):
         return new_function(target_function, *args, **kwargs)

     return _inject  

# decorator injection.
def inject_to(target_object, target_function_name):

     def _inject_to(new_function):
         target_function = getattr(target_object, target_function_name)
         setattr(target_object, target_function_name, inject(target_function, new_function))
         return new_function

     return _inject_to

Original method, that I want to replace with my method:

@macros.macro
class Logger:
    __qualname__ = 'Logger'
    suppress = False

    def exception(self, message, *args, exc=None, log_current_callstack=True, level=150, owner=None, trigger_breakpoint=False):
        if Logger.suppress:
            return

My method:

@injector.inject_to(Logger, 'exception')
def exception(original, self, *args, **kwargs):

    f.writeLine("Logger.exception !!!")
    f.writeLine("original" + str(original))
    f.writeLine("self" + str(self))
    f.writeLine("args" + str(*args))
    f.writeLine("kwargs" + str(**kwargs))

This injector works fine with functions like def update_progress(self):, but for Logger.exception it doesn't work.

Interesting moment - when my method was injected, it doesn't work and original method Logger.exception doesn't executed too.

So, can I ask you two questions?

How to correctly replace Logger.exception with my method?
How to correctly call original Logger.exception in my method, how to correctly pass arguments to the original function?

Do you really think all those try catch blocks are strictly necessary? — Mad Physicist, Feb 01 '18 at 09:03
@juanpa.arrivillaga. there's definitely a little cruft here, but it's pretty minimal already if you forgive a few log statements and comments. — Mad Physicist, Feb 01 '18 at 09:11
In particular, please explain exactly what you mean by "it doesn't work". e.g., if you are getting an error message, provide the error message and stack trace. If you are expecting some behavior, please describe it, and describe the behavior you are seeing instead. — juanpa.arrivillaga, Feb 01 '18 at 09:13
This code was not executed, without any error message or exception. It just "doesn't work" :) — Arthur, Feb 01 '18 at 09:14
Why is `original` being passed as the first argument to `exception`? — juanpa.arrivillaga, Feb 01 '18 at 09:23
@Arthur. I don't recommend using this, but check out https://stackoverflow.com/q/17862185/2988730. I think your way is much cleaner though. — Mad Physicist, Feb 01 '18 at 10:33

Mad Physicist · Accepted Answer · 2018-02-01T14:14:10.480

The fundamental problem you have is that you assign the output of inject to a method attribute. The result of inject always accepts the original function as its first argument, while a method is always invoked with self as the first parameter. There is no amount of decorators in the world that will change this for you, so you will have to work around it.

Whatever inject_to assigns in the line setattr(target_object, target_function_name, ...) must accept self as a first parameter. Just rewrite _inject to accept self first. Perhaps allow both versions and add a boolean parameter to inject. Also change the order of the arguments to your version of exception:

def inject(target_function, new_function, method=False):
    if method:
        @wraps(target_function)
        def _inject(self, *args, **kwargs):
            return new_function(self, target_function, *args, **kwargs)
    else:
        @wraps(target_function)
        def _inject(*args, **kwargs):
            return new_function(target_function, *args, **kwargs)

    return _inject

...
setattr(target_object, target_function_name, inject(target_function, new_function, method=True))
...

@injector.inject_to(Logger, 'exception')
def exception(self, original, *args, **kwargs):
    ...

Thank you for your solution, but it couldn't be compiled - `*** Sorry: IndentationError: unindent does not match any outer indentation level (injector_v2.py, line 25)` - it fails on `return _inject`of method `def inject(target_function, new_function, method=False):` — Arthur, Feb 01 '18 at 11:54
I think, you should remove last `return _inject` from your example and to add into the `if` and `else` sections — Arthur, Feb 01 '18 at 11:59

Method injecting not working

1 Answers1