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Start your free trialChad Goldsworthy
4,209 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?
2 Answers
Chris Freeman
Treehouse Moderator 68,428 PointsGood question. The behavior of __iadd__
is up to the designer. In this case, __iadd__
method, self + other
is evaluated which triggers a call to __add__
. The method __add__
returns an int
or a float
type object. This int
or 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 NumString
then __iadd__
should return self
instead of self.value
:
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!
Chad Goldsworthy
4,209 PointsA ha ! I get it now, thank you Chris.