str() And repr()

Stringification And Representation

  • str(obj): nicely made-up string, used by e.g. print()

  • repr(obj): object representation, ideally suitable as eval() input

  • Default: prints something useless (class name and object identity)

    class Person:
    def __init__(self, firstname, lastname):
        self.firstname = firstname
        self.lastname = lastname

person = Person('Joerg', 'Faschingbauer')

  • Expicitly calling str() on object

    str(person)

    '<__main__.Person object at 0x7fb53e5515b0>'

  • Using print() with an object calls str() on is own

    print(person)

    <__main__.Person object at 0x7fb53e5515b0>

  • repr() on an object

    repr(person)

    '<__main__.Person object at 0x7fb53e5515b0>'

  • print() a list of objects ⟶ uses repr() on list elements

    print([person])

    [<__main__.Person object at 0x7fb53e5515b0>]

Overloading str() And repr(): __str__(), __repr__()

  • __str__(): returns human readable string, describing the object. Called, for example, by print().

  • __repr__(): object representation. Usually the code to re-construct the object.

    class Person:
    def __init__(self, firstname, lastname):
        self.firstname = firstname
        self.lastname = lastname

    def __str__(self):
        return f'{self.firstname} {self.lastname}'

    def __repr__(self):
        return f'Person("{self.firstname}", "{self.lastname}")'

    person = Person('Joerg', 'Faschingbauer')

  • str() (and print())

    str(person)

    'Joerg Faschingbauer'

    print(person)

    Joerg Faschingbauer

  • repr() (and print() on lists)

    print(repr(person))

    Person("Joerg", "Faschingbauer")

    print([person])

    [Person("Joerg", "Faschingbauer")]