Why does the below code throw typeError?

Question

class Car:
    def __init__(self, mileage, make, model):
        self.mileage = mileage
        self.make = make
        self.model = model

    def printCar(self):
        return "The Model is:" + self.model + " the make is: " + self.make + " and the mileage is: " + self.mileage


car = Car(100, 'Suzuki', 'Brezza')

print(car.printCar())

Error Seen: return "The Model is:" + self.model + " the make is: " + self.make + " and the mileage is: " + self.mileage TypeError: must be str, not int

Please help, i am a beginner in python...

This means that you cannot concatenate **integers** (the mileage, the number 100) and **strings**. You need to use the `str()` function to fix it : return "The Model is:" + self.model + " the make is: " + self.make + " and the mileage is: " + str(self.mileage) — NanoPish, Aug 01 '18 at 14:42
Just replace `self.mileage = mileage` by `self.mileage = str(mileage)` and everything else stays the same — Sheldore, Aug 01 '18 at 14:46
Also note that repeated concatenation like this is quite inefficient, as it has to create a temporary string for the result of *each* concatenation. For a scenario like this, you can avoid that cost *and* avoid needing to worry about types (the default behavior of format strings already stringifies inputs) using format strings, changing your code to `return "The Model is:{} the make is: {} and the mileage is: {}".format(self.model, self.make, self.mileage)` (or on Python 3.6 with f-strings, `return f"The Model is:{self.model} the make is: {self.make} and the mileage is: {self.mileage}"`). — ShadowRanger, Aug 01 '18 at 14:46
@Bazingaa: You probably don't want to change the `mileage` attribute to be a `str` permanently; mileage is naturally numeric, and you'd want to be able to work with it numerically (drive the car 10 miles, reflect it with `self.mileage += 10`). Converting to `str` should be done only to produce formatted output. — ShadowRanger, Aug 01 '18 at 14:48
Well, my answer was of course in the scope of OP's posted framework/question. It is understood that strings can't work in numerics. That is why wrote everything else stays the same because there is only a single return statement and no other numerics. But given the OP is beginner, probably you're right — Sheldore, Aug 01 '18 at 14:51
Additional side-note: Normally, you wouldn't make a `printCar` method like this; you'd just define the `__str__` special method (same prototype as `printCar`, just change the name to `__str__`), which would allow seamless conversion to string (you could just do `print(car)`, not `print(car.printCar())`). — ShadowRanger, Aug 01 '18 at 15:10

score 1 · Answer 1 · edited Aug 01 '18 at 14:53

1

def printCar(self):
    return "The Model is:" + self.model + " the make is: " + self.make + " and the mileage is: " + str(self.mileage)

Notice the str function that converts int to string.

edited Aug 01 '18 at 14:53

Alexander

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answered Aug 01 '18 at 14:42

Amitay Dror

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Why does the below code throw typeError?

1 Answers1