CODEWITHSUNDEEP
python
Jer_TX
Jer_TX

Reputation: 474

Confusion with Python for loop and range()

Here's my for loop that does stuff:

for x in range(0, 100):
    currentRate10 = srall10[x].current_rate
    startRate10 = srall10[x].start_rate
    lessons10 = srall10[x].sr_completed
    if currentRate10 is not None and startRate10 is not None:
        gain10 = currentRate10 - startRate10
    else:
        gain10 = 0
    rateavg = gain10 / lessons10

rateavg returns 1.42. Seems accurate to me. However, when I put a variable in place of the 100 OR anything above 100, I get 0 returned back. So if I change 100 to 101, rateavg returns 0. If I put in a variable that contains 143, I still get 0.

srall10 contains a list 

srall10 = DBSession.query(Summary).filter(Summary.sid == 6933).filter(
    Summary.sr_completed.between(1, 10)).all()

There are 143 entries, this was found by the exact same query except with count() at the end instead of all()

Any ideas?

Upvotes: 0

Views: 111

Answers (2)

Bogdan Iulian Bursuc
Bogdan Iulian Bursuc

Reputation: 2275

You get rateavg as the result of the last item. and range(0, 100) will not iterate over all elements. Instead iterate directly over the list.

l = []
for s in srall10:
    if s.current_rate is not None and s.start_rate is not None:
        gain10 = s.current_rate - s.start_rate
    else:
        gain10 = 0
    l.append(gain10 / lessons10)  # average if each item

# total average
total_average = sum(l) / len(l)

Upvotes: 2

Larry Lustig
Larry Lustig

Reputation: 50970

Python will always return an integer value for the division of two integers, so when a division operation in Python returns 0 and you were expecting a number, the first thing to check is whether both the dividend and the divisor are integers. If so, and if the dividend is less than the divisor, then you'll get 0 instead of a float between 0 and 1.

You can avoid this with:

 rateavg = (gain10 * 1.0) / lessons10

I don't know if this is your problem since there's not enough information in the question to determine the type of the values in your lists, but it's often my problem when division unexpectedly returns 0.

Upvotes: 0

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