why exec should never be used in the calling code's namespace? setting class instance attributes with exec

Question

I ve searched the forum but i couldnt exactly find what im looking for.

I have this code where i have many attributes in a class (more than 300 lines) because it's a gui with a lot of stuff. I have therefore made a function with exec which can set the attributes dynamically.

MyClass():
    #some code
    def set_attributes(self,name,chain_index):
        exec(f'self.{name}chk.set(self.chaines01[0][{chain_index}])')
        exec(f'self.{name}dateEntry.delete(0, "end")')
        exec(f'self.{name}dateEntry.insert(0, self.listdates[{chain_index}])')
        exec(f'self.{name}commentEntry.delete(0, "end")')
        exec(f'self.{name}commentEntry.insert(0, self.listcomments[{chain_index}])')

    self.set_attributes('attribute1',1)
    self.set_attributes('attribute2',1)
    ...

However, I'm not sure it's a very pythonic way to do and i dont know well the caution around exec and im not sure the attributes are instanciated correctly in 'self'.

I've seen here https://lucumr.pocoo.org/2011/2/1/exec-in-python/ that i could do exec in a dictionnary :

>>> code = compile('a = 1 + 2', '<string>', 'exec')
>>> ns = {}
>>> exec code in ns
>>> print ns['a']
3

But I want to implement class instance attributes with tkinter features...

I've also seen in another post where they use types.MethodType. Should I use types.MethodType(self.{name}chk.set(self.chaines01[0][{chain_index}]), self) ? on each attributes in the def_attributes function? Or types.DynamicClassAttribute?

How could i replace exec with a more pythonic function that would do the same as exec without using exec?

score 0 · Accepted Answer · answered Mar 29 '22 at 15:54

looking at How is types.MethodType used? it seems i cant assign an attribute to a class instance with types.MethodType as it requires a callable.

looking at What is a DynamicClassAttribute and how do I use it? it seems DynamicClassAttribute is used for metaclass attributes issues and wont be of any use for grounding an attribute to 'self'.

I tried exec in a testClass with self.attribute= and with setattr(self,attribute,value) and the attribute is set properly.

However i ve read exec should never be used in the calling code's namespace.

I have finally found a good way to avoid exec conflicting with local namespaces:

exec(compile(f'self.{name}chk.set(self.chaines01[0][{chain_index}])', '<string>', 'exec')) in self.__dict__

It works fine

why exec should never be used in the calling code's namespace? setting class instance attributes with exec

1 Answers1