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Python: how to utilize instances of a class

New to OOP and python, I am struggling enormously to grasp what good classes actually are for. I tried to ask help from a lecturer who said "oh, then you should read about general methods to classes". Been putting in a days work but get no where.
I get it that a class allow you to collect an instance structure and methods to it, like this:
class Items:
def __init__(self, item_id, item_name):
self.item_id = item_id
self.item_name = item_name
def show_list(self):
print(self.item_id, self.item_name)
idA = Items("idA", "A")
idA.show_list()
But what is even the point of a class if there were not MANY instances you would classify? If I have a method within the class, I must hard code the actual instance to call the class for. What if you want a user to search and select an instance, to then do operations to (e.g. print, compute or whatever)??
I thought of doing it like this:
class Items:
def __init__(self, item_id, item_name):
self.item_id = item_id
self.item_name = item_name
def show_list(self):
print(self.item_id, self.item_name)
idA = Items("idA", "A")
idB = Items("idB", "B")
select_item = input("enter item id")
select_item.show_list()
Replacing hard coded variable with input variable doesn't work, probably logically. I then played with the idea of doing it like this:
class Items:
def __init__(self, item_id, item_name):
self.item_id = item_id
self.item_name = item_name
iL = [Items('idA', 'A'), Items('idB', 'B')]
selected_item = input("enter item id")
for selected_item in iL:
print(f'{selected_item.item_id} {selected_item.item_name}')
Now all are called thanks to making it a list instead of separate instances, but how do I actually apply code to filter and only use one instance in the list (dynamically, based on input)?
I would love the one who brought me sense to classes. You guys who work interactively with large data sets must do something what I today believe exist in another dimension.
See examples above^^

It seems you want to find all the instances of a certain element within a class.
This is as simple as:
print([x for x in iL if x.item_id == selected_item])
Now, you may ask why you can't just store the elements of iL as tuples instead of classes. The answer is, you can, but
("idA", "A")
is much less descriptive than:
item_id = "idA"
item_name = "A"
Any code you write with classes, you should in theory be able to write without classes. Classes are for the benefit of the coder, not the end-user of the program. They serve to make the program more readable, which I'm sure you'll find is a desirable property.

Your point here is to lookup for Items instances based on their item_id attribute.
That's a thing to create instances of a class.
It's a completely different thing to search for items objects stored in memory - that is not directly linked to the concept of OOP, classes and instances.
You could use dictionary to store references of your objects and then lookup in your dictionary.
class Items:
def __init__(self, item_id, item_name):
self.item_id = item_id
self.item_name = item_name
def show_list(self):
print(self.item_id, self.item_name)
idA = Items("idA", "A")
idB = Items("idB", "B")
lookup_dict = {"idA": idA, "idB": idB}
select_item = input("enter item id")
found_item = lookup_dict.get(select_item)
if found_item:
found_item.show_list()
else:
print(f"item {select_item} not found")

Python Count function not work on instances of a class?

So Ive been trying to make a method which checks if an entered Item is present in the players inventory. For that I used the count to check if the item exists atleast once. However it seems like that it does not instances of the class. (All the items in the inventory of the player are instance of a classs)
inventory = []
def equipItem(self):
equipinput = input("Chosse Item to equip: ")
#Get Input which item to equip
itemcount = self.inventory.count(equipinput)
#Count how many times the item was found
if itemcount >= 1:
itemindex = self.inventory.index(equipinput)
if self.inventory[itemindex].typeitem == "weapontype":
#Check the item type(is an attribute of the item/Class)
self.inventory[0], self.inventory[itemindex] = self.inventory[itemindex], self.inventory[0]
#Switch position of the item to equip and that of the current item (It is always on the first position)
print("Changed Weapon to " + str(equipinput))
game()
#Go back to the game
else:
self.inventory[1], self.inventory[itemindex] = self.inventory[itemindex], self.inventory[1]
print("Changed Armor to " + str(equipinput))
game()
else:
print(f"{Fore.RED}You do not have this item!{Style.RESET_ALL}")
#Output an error Message in red
game()
Example inventory:
self.inventory = [Wooden Dagger, Steel Sword]
Example input would be then: Steel Sword
Expected Output/inventory:
self.inventory = [Steel Sword, Wooden Dagger]

You are comparing apples to oranges. The returned value of input is type string and the inventory array contains instances of some class (which you have omitted but i will call the "equipment" class).
You could create a __str__(self): method for the omitted "equipment" class like so.
class Equipment:
def __init__(self, name: str):
self.name = name
def __str__(self):
return self.name
You could then use list comprehension to create an array of string representations of the inventory and compare the input to that.
inventory = [Equipment('steel sword'), Equipment('basic axe')]
def equip_item(self):
string_inventory = [str(item) for item in self.inventory] # creates array ['steel sword', 'basic axe']
print(string_inventory.count('basic axe')) # now we can compare strings to strings with the count method
I would also recommend looking into the __repr__(self): magic method.
lastly, if comparing string, I also recommend using the .upper() method so capitalization does not cause problems.

You cannot count instances of a class this way. If you look at the representation of it by printing it, you will see something like <__main__.SteelSword object at 0x7f15e6f97430>. They are obviously different, but are instances of the same class. So you can do:
[isinstance(ins, SteelSword) for ins in self.inventory].count(True)
Now, if you use input(), you will always get a string back, which is different from a class reference: 'SteelSword' != <class '__main__.SteelSword'>
So you need a way to address this issue. What you could do, for example, is to create a dict that takes your class names as a string ('SteelSword') key and the class references as the corresponding values.

How to make nested enum also have value

Consider the following code example:
from enum import Enum
class Location(Enum):
Outside = 'outside'
Inside = 'inside'
class Inside(Enum): # TypeError for conflicting names
Downstairs = 'downstairs'
Upstairs = 'upstairs'
How do I make Inside have the value 'inside' whilst also being a nested enum for accessing Downstairs and Upstairs?
Desired input:
print(Location.Inside)
print(Location.Inside.value)
print(Location.Inside.Downstairs)
print(Location.Inside.Downstairs.value)
Desired output:
Location.Inside
inside
Location.Inside.Downstairs
downstairs
UPDATE 1:
Some more context to my specific problem:
class Location(Enum):
Outside = 'outside'
Inside = 'inside'
class Inside(Enum): # TypeError for conflicting names
Downstairs = 'downstairs'
Upstairs = 'upstairs'
class Human:
def __init__(self, location):
self.location = location
def getLocationFromAPI():
# this function returns either 'inside' or 'outside'
# make calls to external API
return location # return location from api in str
def whereInside(human):
if human.location != Location.Inside:
return None
# here goes logic that determines if human is downstairs or upstairs
return locationInside # return either Location.Downstairs or Location.Upstairs
location_str = getLocationFromAPI() # will return 'inside' or 'outside'
location = Location(location_str) # make Enum
human = Human(location) # create human with basic location
if human.location == Location.Inside:
where_inside = whereInside(human)
human.location = where_inside # update location to be more precise
The problem is when I create the Human object I only know of a basic location, as in 'inside' or 'outside'. Only after that can I update the location to be more precise.

You can accomplish this by embedding an enum.Enum inside another like so: (just watch out for names conflicting)
from enum import Enum
class _Inside(Enum):
Downstairs = 'downstairs'
Upstairs = 'upstairs'
class Location(Enum):
Outside = 'outside'
Inside = _Inside
print(Location.Inside.value.Downstairs.value)
downstairs

it may be a bit late and the one who asked the question is no longer necessary, but I leave it here in case someone wants to take a look at it, and even if it has already been validated as one, although the same comment that it is not completely complete .
But I have been thinking about it and in the end I have solved it by looking at the same documentation XD.
You cannot extend classes of Enums, but you can extend methods, I have followed this way and the only thing I have done has been to override the new and init methods, the use case can be modified, this is only to nest enumerators.
from enum import Enum
class SuperNestedEnum(Enum):
def __new__(cls, *args):
obj = object.__new__(cls)
value = None
# Normal Enumerator definition
if len(args) == 1:
value = args[0]
# Have a tuple of values, first de value and next the nested enum (I will set in __init__ method)
if len(args) == 2:
value = args[0]
if value:
obj._value_ = value
return obj
def __init__(self, name, nested=None):
# At this point you can set any attribute what you want
if nested:
# Check if is an Enumerator you can comment this if. if you want another object
if isinstance(nested, EnumMeta):
for enm in nested:
self.__setattr__(enm.name, enm)
class Homework(Enum):
Task = "5"
class Subjects(SuperNestedEnum):
Maths = "maths"
English = "english"
Physics = "nested", Homework
class School(SuperNestedEnum):
Name = "2"
Subjects = "subjects", Subjects
Ignore the use case because it doesn't make sense, it's just an example
>>> School.Name
<School.Name: '2'>
>>> School.Subjects
<School.Subjects: 'subjects'>
>>> School.Subjects.value
'subjects'
>>> School.Subjects.Maths
<Subjects.Maths: 'maths'>
>>> School.Subjects.Physics.value
'nested'
>>> School.Subjects.Physics.Task
<Homework.Task: '5'>
>>> School.Subjects.Physics.Task.value
'5'

If anyone has similar issues and just wants a simple solution for the topic without patching any functions or additional imports for enums containing strings, follow these steps:
Create the value enums, in your lower hierarchy, like:
class __private_enum1__(str, enum.Enum):
VAL11 = "abc"
VAL12 = "def"
class enum2(str, enum.Enum):
VAL21 = "123"
VAL22 = "456"
Create a base class (a container) for these enums. Where you can either import the enums classes or simply directly acccess the enums.
class myValues:
VAL11 = __private_enum1__.VAL11
VAL12 = __private_enum1__.VAL12
VALS2X = enum2
Then you can access your values by:
print(myValues.VAL11.value)
print(myValues.VAL2X.VAL21.value)
.value is not necessary here but it shows that you both access the string inside the enum for passing it to other functions but also the enum itself, which is pretty neat. So basically, first create the values, then the structure. That way you have a class but it provides you the basic functionality of enums and you can nest them as deep as you want to without further imports.

How can I check if an attribute of a class exists in array?

I want to know if it is possible to check if an array of a class has a specific instance of an attribute, and return True if it does. In other words, does an instance of a class attribute exist in an array of that class?
In my example, I have an array of class Team. The class Team has an attribute, name. I want to check if a Team instance with a specific name exists by iterating over an array of Team instances.
Class Team:
class Team:
def __init__(self):
self.name = name # (String)
[Invalid] This is the how I wanted to write the function:
# team_name is a String variable
# teams is an array of the Team class
def team_name_taken(team_name, teams):
if team_name in teams.name:
return True
else:
return False
I know this doesn't work, but is it possible to iterate over the same attribute within an array in this fashion?
[Valid] Regarding the goal of my code, I have the following code that works properly:
def team_name_taken(team_name, teams):
for team in teams:
if team_name == team.name:
return True
return False
I know that this works, I was just wondering if there was another way to do it, similar to the invalid way I represented above.

What you could do is the following:
def team_name_taken(team_name, teams):
team_names = [team.name for team in teams]
if team_name in team_names:
return True
else:
return False
This will generate a list with the items of the list being all team names. Once you have done that you can do if team_name in team_names: and get the desired outcome.
If on the other hand you just want to make it a oneliner you could do this:
def team_name_taken(team_name, teams):
return len([ team for team in teams if team.name == team_name ]) >= 1
This will make a list then check if the len() of the list is 1 (or bigger) and if that is the case return True else False.

The following class definition allows name from the user to be assigned to the Team.name attribute and forces it to be a str object:
class Team(object):
def __init__(self, name):
self.name = str(name)
Here is an example list of Team instances:
teams = [Team(x) for x in range(10)]
You can do what I think you want with some one-liners:
Using another list comprehension to find out if any of the names equal '3':
any([team.name == '3' for team in teams])
Or if you really want to use a function you can use the following:
any(map(lambda obj: obj.name == '3', teams))

python: Using the choice box to get data besides getString()

I have defined an object that has several attribute..
class thing(object):
def __init__(self, type, name, attrA, attrB, attrC):
self.type = type
self.name = name
self.attrA = attrA
self.attrB = attrB
self.attrC = attrC
lets say then I have a list of things
self.things=[thing('car','fred',1,2,3),
thing('car','george',a,b,c),
thing('truck','bob',6,7,8),
thing('truck','tom',x,y,z)
]
I then populate a choice box with SOME of the items from that list
for each in self.things:
if each.type == 'car':
self.choiceCar.Append(item=each.name)
When the user selects Bob from the dropdown I have an event for that
def EvtChoice(self,event):
self.Name = event.GetString()
This captures the name of the selection, but how do I get the other attributes? What I am currently doing is
for each in self.items:
if self.Name == each.name
#Get other things here
My thought is that if my list grows large then this loop through my entire list will become very inefficient and really unneeded since the user has already selected the specific item I want. What I think I should be able to do is to get the index of the selected item, but im not sure how to do that, or even if that is the correct way to go about it.

Associating data or objects with wx.Choice or wx.ComboBox is pretty easy. You can see an example using the latter here:
http://www.blog.pythonlibrary.org/2010/12/16/wxpython-storing-object-in-combobox-or-listbox-widgets/
The basic idea is to pass an empty list to the control's constructor and then iterate over the objects and Append them to the control. So something like this:
for obj in self.things:
self.choiceCar.Append(obj.name, obj)
Then in the event handler for the widget, you can get the object back by doing this:
obj = self.choiceCar.GetClientData(self.choiceCar.GetSelection())