Multiple Assignment a = b = c

srinivas devaki mr.eightnoteight at
Tue Feb 16 07:46:45 EST 2016


a = b = c

as an assignment doesn't return anything, i ruled out a = b = c as
chained assignment, like a = (b = c)
SO i thought, a = b = c is resolved as
a, b = [c, c]

at-least i fixed in my mind that every assignment like operation in
python is done with references and then the references are binded to
the named variables.
like globals()['a'] = result()

but today i learned that this is not the case with great pain(7 hours
of debugging.)

class Mytest(object):
    def __init__(self, a):
        self.a = a
    def __getitem__(self, k):
        print('__getitem__', k)
        return self.a[k]
    def __setitem__(self, k, v):
        print('__setitem__', k, v)
        self.a[k] = v

roots = Mytest([0, 1, 2, 3, 4, 5, 6, 7, 8])
a = 4
roots[4] = 6
a = roots[a] = roots[roots[a]]

the above program's output is
__setitem__ 4 6
__getitem__ 4
__getitem__ 6
__setitem__ 6 6

But the output that i expected is
__setitem__ 4 6
__getitem__ 4
__getitem__ 6
__setitem__ 4 6

SO isn't it counter intuitive from all other python operations.
like how we teach on how python performs a swap operation???

I just want to get a better idea around this.

Srinivas Devaki
Junior (3rd yr) student at Indian School of Mines,(IIT Dhanbad)
Computer Science and Engineering Department
ph: +91 9491 383 249
telegram_id: @eightnoteight

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