Iterating through a list with dataclasses, and checking if an element matches the inputted int?

Question

I"m having a bit of trouble with my code. I’m trying to get the IDs from the list and compare it to an int input. If the int is the same as the ID, it’ll print("Yes"). If it doesn’t match an ID, it’ll print("no"). Problem is, it’s printing no for even the numbers that should return yes to..

from dataclasses import dataclass


@dataclass
class Dog:
    ID: int
    name: str


dog_details = [
    Dog(
        ID=1,
        name="Toby"),
    Dog(
        ID=2,
        name="Rex",
    ),
    Dog(
        ID=3,
        name="Sandy",
    ),
    Dog(
        ID=4,
        name="Wanda",
    ),
    Dog(
        ID=5,
        name="Toto",
    ),
]

while True:
    for index in range(len(dog_details)):
        identification = int(input("What ID? "))
        if identification != dog_details:
            print("no")
        elif identification == dog_details:
            print("Yes")

I’m toying with variations of:



while True:
    for index in range(len(dog_details)):

        identification = int(input("What ID? "))
        if identification != dog_details:
            print("no")
        elif identification == dog_details:
            print("Yes")

Problem is, it is saying no for every number inputted.

Asked By: regexted

||

Source

Answer 1

dog_details is a list of Dogs; it will never be equal to an int.

What I think you might want is:

while True:
    for dog in dog_details:
        identification = int(input("What ID? "))
        if identification == dog.ID:
            print(f"Yes, this is {dog.name}")
        else:
            print(f"no, this is {dog}")

Note that because you’re asking for an ID inside the for loop, you’re comparing the ID to a specific dog in the list. (I added that dog to the print statement so that when it says "no" you can see what dog it was comparing your ID to.) If you want to compare it to all the dogs and return the matching one, do:

dogs_by_id = {dog.ID: dog for dog in dog_details}
while True:
    identification = int(input("What ID? "))
    if identification in dogs_by_id:
        print(f"Yes: {dogs_by_id[identification].name}")
    else:
        print("no")

The first line creates a dict that will allow you to look up a dog by its ID. If you were to do this without a dict, it’s more complicated; you need to loop through the entire list each time, something like:

while True:
    identification = int(input("What ID? "))
    for dog in dog_details:
        if dog.ID == identification:
            print(f"Yes: {dog.name}")
            break
    else:
        print("no")

Answered By: Samwise

Answer 2

You wanted to compare ID against identification.

identification = 0
while identification >= 0:
    identification = int(input("What ID? "))
    found_dog = None

    for dog in dog_details:
        if dog.ID == identification:
            found_dog = dog

    if found_dog:
        print("Yes!", found_dog)
    else:
        print("No.")

Type -1 or CTRL-C to exit the loop.

Answered By: J_H

Answer 3

You have to use the ID attribute of the Dog class to access the Dog instance’s ID (int); then you can check for equality, and your program should behave as expected.

from dataclasses import dataclass


@dataclass
class Dog:
    ID: int
    name: str

dog_details = [
    Dog(ID=1, name="Toby"),
    Dog(ID=2, name="Rex"),
    Dog(ID=3, name="Sandy"),
    Dog(ID=4, name="Wanda"),
    Dog(ID=5, name="Toto"),
]

dog_ids = set(d.ID for d in dog_details)
while True:
    id_ = int(input("What ID? "))
    if id_ not in dog_ids:
        print('no')
    else:
        print('yes')
        break

Answered By: irahorecka

Iterating through a list with dataclasses, and checking if an element matches the inputted int?

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