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Chad Goldsworthy4,209 Points
__iadd__ changes the data type?
I saw someone else ask this, but the question was still a bit unresolved. When including the iadd method in the class, it changes the data type. For example, with the class show in this video:
class NumString: def __init__(self, value): self.value = str(value) def __str__(self): return self.value def __int__(self): return int(self.value) def __float__(self): return float(self.value) def __add__(self, other): if "." in self.value: return float(self.value) + other return int(self.value) + other def __radd__(self, other): return self + other def __iadd__(self, other): self.value = self + other return self.value
Now, for example, if I were to use the regular add operator:
age = NumString(5) age + 5 print(age.__class__.__name__) # this would return "NumString" age.value # this would return "5"
But if I were to use the in place add operator:
age += 1 print(age.__class__.__name__) # this would return "int" age.value # this returns an AttributeError
So using the dunder iadd method changes the variables data type, is this expected? What if you didn't want it to change the data type?
Chris FreemanTreehouse Moderator 67,995 Points
Good question. The behavior of
__iadd__ is up to the designer. In this case,
self + other is evaluated which triggers a call to
__add__. The method
__add__ returns an
int or a
float type object. This
float is assigned to
self.value, but then the
self.value is returned. This is what is assigned to the left-side of the statement and where the new type comes from.
If you wanted to keep the object type as
__iadd__ should return
self instead of
class Numstring: def __iadd__(self, other): self.value = str(self + other) # use str() to keep value correct return self >>> age = NumString(5) >>> age.value '5' >>> age += 6 >>> age <__main__.NumString object at 0x7f630f78a860> >>> age.value '11' >>> age = NumString(5) >>> age.value '5' >>> age + 7 12 >>> age.value '5' >>> age += 7 >>> age.value '12' >>> type(age) <class '__main__.NumString'>
Post back if you have more questions. Good luck!