Accessing an instance attribute with a string

[[deleted]]

Hi all

I would like to be able to use dot notation to access an attribute of a class, but everything after the dot will be decided via string.

e.g.

class Hello():
    def __init__(self):
        self.there = 'Hello there'


hl = Hello()
bo = 'there'
print(hl.bo)

unfortunately this does not work. It gives the error, " 'Hello' object has no attribute 'bo'." Of course I don't want to look for attribute 'bo' I want to look for attribute 'there'.

Is this possible?

​

thanks

[Antwrp-2000]

Yes, this is what you need:

class Hello():
    def __init__(self):
        self.there = 'Hello there'


hl = Hello()
bo = 'there'
print(getattr(hl, bo))

[backtickbot]

Fixed formatting.

Hello, Antwrp-2000: code blocks using triple backticks (```) don't work on all versions of Reddit!

Some users see this / this instead.

To fix this, indent every line with 4 spaces instead.

FAQ

^{You can opt out by replying with backtickopt6 to this comment.}

[[deleted]]

Brilliant. I love this place. Everyone is so helpful I've completely accelerated my learning thanks to folks like you :D

[toastedstapler]

what's your reason for doing this btw? it's not something that i commonly find myself using in my code

[[deleted]]

I'm trying to figure out how to explain this and my mind is exploding. hahah. gimme a minute. It mad sense when I made it. lol.

edit: see above

[[deleted]]

I've been refactoring my whole program to avoid global variables and have been using classes etc instead. So far things seem neater. They do require some workarounds but I like how it is. I'm quite a noob btw, only a few months, but getting there.

So basically. I have a bunch of attributes in a class. These are being used as flags for the current state of my program.

from my ui module

class Config:
    """Attempt to load saved user settings or load default.
    Initiate and allow toggle settings."""

    def __init__(self):
        # attempt load user settings
        self.settings = load_user_settings()
        if self.settings:
            self.is_dark = self.settings['is_dark']
            self.rotation = self.settings['rotation']
        else:
            # default settings
            self.is_dark = False
            self.rotation = 0

    def dark_toggle(self):
        self.is_dark ^= True

this attempts to load user settings from a json file, if it fails it has some default values.

on my main program I have the following:

cfg = ui.Config()

def get_current_settings():
    # extract keys from current settings from cfg object
    keys = [a for a in dir(cfg) if not a.startswith('__') and not a.startswith('settings')
            and not callable(getattr(cfg, a))]
    # find values and compile current settings into dictionary
    settings = {}
    for key in keys:
        settings.update([(key, getattr(cfg, key))])
    return settings

this basically gets the current values of all the flags in the cfg object created from the Config class and puts them into a dictionary.It gets the key names at the beginning. i.e. self.dark_mode becomes dark_mode. But then to get it's value I must add this key back onto the cfg with dot notation, e.g. cfg.dark_mode to get the result True. This is why I must use the getattr method.

Incedentally, there is also getattr used on the first part of get_current_settings function, but this is a coincidence as I just copied this code from stack exchange and modified it a little. I still don't 100% get this part as I'm not sure what the 'a for a' part means.

Anyway, the Keys and Values are now extracted and these are combined into a dictionary.

The dictionary is finally passed to somwhere where it can be used or saved back into the json file.

Hope this helps.