[FIXED] How do I pull a given method passed as a string in a user defined function

Issue

I'm trying to create a user defined function in which one of the arguments is a method (s_method) to be applied to a sequence (seq) and args_ are the arguments for s_method. However, for simplicity, I'm only using lists as a sequence type here:

def this_function(args_, s_method, seq):

    arguments = locals()
    
    if type(seq) == list:
        if s_method not in dir(type(seq)): # dir(type())
            print('Method not found or some other error message here.')
        else:
          res_ = seq.arguments['s_method'](arguments['args_'])

    return res

The expected output after calling the function would be:

new_list = this_function([1, 5], 'append', [3, 4, 2, 104])
print(new_list)

>>> [1,5,[3,4,2]]

what I want the function to do is seq.append(args_)

but, for some reason res_ = seq.arguments['s_method'](arguments['args_']) is not working as intended, so I'm getting this error :

--------------------------------------------------------------------------------
AttributeError                            Traceback (most recent call last)
<ipython-input-89-b8df0448c005> in <cell line: 1>()
----> 1 output = this_function([1, 5], 'append', [3, 4, 2, 104])
      2 print(output)

<ipython-input-88-6f8d5897c15c> in this_function(args_, s_method, seq)
     11                    'some error message here.')
     12         else:
---> 13           res_ = seq.arguments['s_method'](arguments['args_'])
     14 
     15     return res

AttributeError: 'list' object has no attribute 'arguments'

It's supposed to insert append instead of 'arguments' but this doesn't happen.

Evaluating separately I noticed that with everything I tried so far, I keep getting 'append' which is a string... so, it's not the same as append and therefore, every error is very much the same thing "no such attribute exists".

I've tried

seq_1 = [3, 4, 2, 104]
args_1 = [1, 5]
seq_method = 'append'

seq_2 = seq_1.seq_method([1, 5])
print(seq_2)

then,

seq_method = eval('seq_1.seq_method([1,5])')
print(seq_method)

but I get same error, and getattr() returns

<function list.append(object, /)>

but I couldn't work out how to use it to extract append from it.

Any help and suggestions much appreciated

Solution

If you want to call append() by string name on seq_1 then getattr() is what you are looking for:

seq_1 = [3, 4, 2, 104]
args_1 = [1, 5]
seq_method = 'append'
getattr(seq_1, seq_method)(args_1)
print(seq_1)

Gives you:

[3, 4, 2, 104, [1, 5]]

Note that append() returns None so you don't get a new list.

If you want a new list you need a comprehension, copy, or to populate nn empty list in a loop.

Answered By - JonSG