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Python Object-Oriented Python Advanced Objects Controlling Conversion

Posted by anthony pizarro
anthony pizarro
1,983 Points

__str__ and so on

why do we need to use str , int , ... to return a value, wouldn't a simple code like value = 6 newIStr = str(value) or newInt = int(value) and so on

1 Answer

Steven Parker
Steven Parker
229,732 Points
Steven Parker
Steven Parker
229,732 Points

The functions like "str()" and "int()" are used to convert values from one type to another, but in the process of performing the conversion, the system will use the "magic" methods ("__str__()", "__int__()", etc.) to actually get the object's value in that other form.

The system knows how to convert the built-in types, but it doesn't know how to convert a custom object unless you provide the method for it.

class foo:    # this class just contains a value
    val = 21

class bar:    # this one also has an "__int__" method
    val = 42
    def __int__(self):
        return self.val

f = foo()     # f is a foo object
b = bar()     # b is a bar object

print(int(f)) # taking the int value of f fails
# TypeError: int() argument must be a string, a bytes-like object or a number, not 'foo'

print(int(b)) # but it works just fine for b
# 42