Python - While-Loop until list is empty

Question

I'm working with Django and I have a queryset of objects that has been converted to a list (unpaid_sales). I'm executing a process that iterates through this list and operates on each item until either the list is empty, or a given integer (bucket) reaches zero.

This is how I set it up:

while unpaid_sales:
    while bucket > 0:
        unpaid_sale = unpaid_sales.pop(0)
        ...do stuff

In some cases, I am getting the following error:

pop from empty list

What's wrong with my logic?

Use a single while with or.

YiFei
– YiFei

2016-10-08 16:23:54 +00:00
Commented Oct 8, 2016 at 16:23 — YiFei
– YiFei, Commented Oct 8, 2016 at 16:23
When does bucket change?

qfwfq
– qfwfq

2016-10-08 16:25:11 +00:00
Commented Oct 8, 2016 at 16:25 — qfwfq
– qfwfq, Commented Oct 8, 2016 at 16:25
I understand now, thank you!

Adam Starrh
– Adam Starrh

2016-10-08 16:26:57 +00:00
Commented Oct 8, 2016 at 16:26 — Adam Starrh
– Adam Starrh, Commented Oct 8, 2016 at 16:26

Joel Carneiro · Accepted Answer · 2021-12-10 11:16:11Z

10

Your end criteria must be formulated a little differently: run the loop while there are items and the bucket is positive. or is not the right operation here.

while unpaid_sales and bucket > 0:
    unpaid_sale = unpaid_sales.pop(0)
    #do stuff

edited Dec 10, 2021 at 11:16

Joel Carneiro

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answered Oct 8, 2016 at 16:27

tynn

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3 Comments

Adam Starrh Over a year ago

They each have their own else conditions. Does elif work with while loops?

tynn Over a year ago

Not realy. But in this case you should probably use a normal if statement after the while loop

Adam Starrh Over a year ago

Got it. Thanks a lot!

MMF · Accepted Answer · 2016-10-08 16:59:33Z

7

Do not use separate whileloops. Do as follows :

while unpaid_sales and bucket > 0 :
    unpaid_sale = unpaid_sales.pop(0)
    ...do stuff

edited Oct 8, 2016 at 16:59

answered Oct 8, 2016 at 16:25

MMF

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Comments

Efferalgan · Accepted Answer · 2016-10-08 16:26:24Z

4

You should do a single loop: while bucket>0 and unpaid_sales. Here, you are popping elements in the bucket loop, and then just just check that bucket is positive, but you do not check that element_sales still has elements in it.

answered Oct 8, 2016 at 16:26

Efferalgan

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