"Three minutes series 04" understanding Python black magic in 3 minutes__ repr__ And__ str__

Hearing people's feathers hanging 2020-11-12 23:16:13
minutes series understanding python black

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__repr__ and __str__ Both methods are used for display ,__str__ It's user oriented , and __repr__ For programmers .

The printing operation will first try __str__ and str Built in functions (print The internal equivalent form of operation ), It should usually return a friendly display .__repr__ For all other environments : It is used for prompt response in interactive mode and repr function , If not used __str__, Will use print and str. It should usually return an encoded string , Can be used to recreate objects , Or give developers a detailed display .

When we want to have a unified display in all environments , Can be refactored __repr__ Method ; When we want to support different displays in different environments , For example, the end-user display uses __str__, Programmers use the underlying... During development __repr__ To display , actually __str__ It's just covered __repr__ For a more user-friendly display .

Here's an example :

class Person(object):
    def __init__(self, name, gender):
        self.name = name
        self.gender = gender
    def __str__(self):

        return '(Person: %s, %s)' % (self.name, self.gender)

Now? , Interactive command line with print try :

>>> p = Person('Bob', 'male')
>>> print p
(Person: Bob, male)
however , If you knock a variable directly p:

>>> p
<main.Person object at 0x10c941890>
Seems to be __str__() Will not be called .

because Python Defined __str__() and __repr__() The two methods ,__str__() Used to display to the user , and __repr__() Used to display to developers .

There is a definition of laziness __repr__ Methods :

class Person(object):
    def __init__(self, name, gender):
        self.name = name
        self.gender = gender
    def __str__(self):
        return '(Person: %s, %s)' % (self.name, self.gender)
    __repr__ = __str__

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