initialization with python list

Question

I have a problem with correct initialization within a list

import random

a = [random.randint(0,1) for x in range(10)] # getting random 0 and 1

b = a[:] # copying 'a' list for purpose of analysis 

for x,y in enumerate(b): # adding + 1 where value is 1
    if y != 0:
        b[x] += b[x-1]



print(a) # > [1, 0, 0, 1, 1, 1, 0, 0, 1, 1]  
print(b) # > [2, 0, 0, 1, 2, 3, 0, 0, 1, 2]
# wanted # > [1, 0, 0, 1, 2, 3, 0, 0, 1, 2]

from a[1:] everything is ok. Python does correct initialization, however if a[0] == 1 and a[9] == 1, Python ofcourse takes a[9] as a start value in my case.

I am just asking if there is any pythonic way to solve this > explaining python to just start initialization from 0 at a[0] and passing a[9] as first value.

Thanks

I'm not sure exactly what you're asking. Your code produces the output I would expect it to, and I think it lines up with your explanation of what you want. Could you clarify what exactly is wrong, and provide what you expect the output to be? — wnnmaw
– wnnmaw, Commented Jun 16, 2016 at 17:52
I like hashcode55's solution. The problem is that b[0-1] references the last item in the list, which could be a 1. — nbryans
– nbryans, Commented Jun 16, 2016 at 17:57

Marcy · Accepted Answer · 2016-06-16 17:56:08Z

2

You can skip the first value rather easily:

for x,y in enumerate(b[1:]): # adding + 1 where value is 1
    if y != 0:
        b[x + 1] += b[x]

b[1:] just skips the first value from the list for the enumeration. This way the first number is untouched. But because the indexes in x are now all one too low, we have to add one in both cases, turning x into x + 1 and x - 1 into x. This way we access the right index.

Using your test list, it produced the following output:

[1, 0, 0, 1, 1, 1, 0, 0, 1, 1]  # original list
[1, 0, 0, 1, 2, 3, 0, 0, 1, 2]  # processed list

answered Jun 16, 2016 at 17:56

Marcy

3,0261 gold badge27 silver badges37 bronze badges

Sign up to request clarification or add additional context in comments.

Collectives™ on Stack Overflow

initialization with python list

1 Answer 1

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

Comments

Your Answer

Sign up or log in

Post as a guest

Related