CODEWITHSUNDEEP
python
tomasz74
tomasz74

Reputation: 16701

Assignment to value returned from list

I have a class with multiple vectors from measurements. I need to iterate over these vectors but would like to use only chosen measurements. The simplified version of what I build so far is below:

import pylab as pl
class IterationReturn(object):
    def __init__(self):
        self.a = (1,2,3,4,5,6,7,8,9)
        self.b = (10,20,30,40,50,60,70,80,90)
        self.c = (-1,-2,-3,-4,-5,-6,-7,-8,-9)
        self.i = 0

    def returnNextSet(self):
        self.aIter = self.a[self.i]
        self.bIter = self.b[self.i]
        self.cIter = self.c[self.i]
        self.i +=1
        return (self.aIter, self.bIter, self.cIter)               

if __name__ == '__main__':
    iteration = IterationReturn()
    for i in range(len(iteration.a)): 
        # x takes aIter value from iteration.returnNextSet()
        # y takes bIter value from iteration.returnNextSet()        
        x,y = iteration.returnNextSet()    
        pl.scatter(x, y)
    pl.show()

I don't want to use x,y,z = iteration.returnNextSet() which would work in this example, but in practice I have many more values and do not want to assign them all. I can't find a way to assign only to aIter and bIter.

I have an error:

    x,y = iteration.returnNextSet()      
ValueError: too many values to unpack

In my problem I have many measurements (a,b, ... ,z) and for example I want to assign x=d and y=k I also think it should be done in different way from the beginning like designing new class with inheritance but not sure how to do that. Would appreciate your help

Upvotes: 0

Views: 91

Answers (3)

kindall
kindall

Reputation: 184405

Just do:

results = iteration.returnNextSet()

Then refer to the values as results[0], results[1], and so on. You can do len(results) to see how many you got.

Upvotes: 1

Andy Hayden
Andy Hayden

Reputation: 375865

The best way to do this is to return a dictionary:

return {'a': self.aIter, 'b':self.bIter, 'c': self.cIter, ...}

Then you can assign:

NS = iteration.returnNextSet()
x, y = NS['x'], NS['y']

.

Keeping your current function, you could assign the first two values:

x, y = iteration.returnNextSet()[:2]

and in Python 3 you will be able to assign the rest of the values to another tuple:

x, y, *args = iteration.returnNextSet()

Upvotes: 1

Jon Clements
Jon Clements

Reputation: 142236

Not quite sure why you'd want to do this, but here's one way:

class Test(object):
    def __init__(self):
        self.a = (1,2,3,4,5,6,7,8,9)
        self.b = (10,20,30,40,50,60,70,80,90)
        self.c = (-1,-2,-3,-4,-5,-6,-7,-8,-9)

    def iter_over(self, *args):
        items = [getattr(self, arg) for arg in args]
        return zip(*items)

t = Test()
for a, c in t.iter_over('a', 'c'):
    print a, c

1 -1
2 -2
3 -3
4 -4
5 -5
6 -6
7 -7
8 -8
9 -9

Or:

for items in t.iter_over('c', 'b', 'a'):
    print items[1] # will be b (or 2nd passed above) etc...

Upvotes: 1

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