On 27/09/2016 17:49, Steve D'Aprano wrote:
I have a class that takes a bunch of optional arguments. They're all
optional, with default values of various types. For simplicity, let's say
some are ints and some are floats:
class Spam:
def __init__(self, bashful=10.0, doc=20.0, dopey=30.0,
grumpy=40, happy=50, sleepy=60, sneezy=70):
# the usual assign arguments to attributes dance...
self.bashful = bashful
self.doc = doc
# etc.
I also have an alternative constructor that will be called with string
arguments.
May I ask: do you really need to add this method? Can't you ensure that
the data passed during initialisation is already of the right type (i.e.
can you convert to float/ints externally)? If now why?
Lorenzo.
It converts the strings to the appropriate type, then calls the
real constructor, which calls __init__. Again, I want the arguments to be
optional, which means providing default values:
@classmethod
def from_strings(cls, bashful='10.0', doc='20.0', dopey='30.0',
grumpy='40', happy='50', sleepy='60', sneezy='70'):
bashful = float(bashful)
doc = float(doc)
dopey = float(dopey)
grumpy = int(grumpy)
happy = int(happy)
sleepy = int(sleepy)
sneezy = int(sneezy)
return cls(bashful, doc, dopey, grumpy, happy, sleepy, sneezy)
That's a pretty ugly DRY violation. Imagine that I change the default value
for bashful from 10.0 to (let's say) 99. I have to touch the code in three
places (to say nothing of unit tests):
- modify the default value in __init__
- modify the stringified default value in from_strings
- change the conversion function from float to int in from_strings
Not to mention that each parameter is named seven times.
How can I improve this code to reduce the number of times I have to repeat
myself?
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