struggling with these problems

MRAB python at mrabarnett.plus.com
Wed Jan 30 04:59:32 CET 2013


On 2013-01-30 03:26, su29090 wrote:
> 1.Given that  worst_offenders has been defined as a list with at least 6 elements, write a statement that defines  lesser_offenders to be a new list that contains all the elements from index 5 of  worst_offenders and beyond. Do not modify  worst_offenders .
>
> I tried this but it didn't work:
>
> lesser_offenders = worst_offenders[5:6]
>
Python uses half-open ranges (and counts from 0), which means that the 
start index is included and the end index is excluded.

Therefore, worst_offenders[5:6] means the slice from index 5 up to, but 
excluding, index 6; in other words, an empty list.

The question says "and beyond"; in Python you can just omit the end 
index to indicate everything up to the end.

> 2.Given a variable  temps that refers to a list, all of whose elements refer to values of type  float , representing temperature data, compute the average temperature and assign it to a variable named  avg_temp . Besides temps and  avg_temp , you may use two other variables --  k and  total .
>
>
> I'm not sure about this one but this is what I have:
>
> for k in range(len(temps)):
> 	total += temps[k]
>
> avg_temp = total / len(temps)
>
You didn't set the initial value of total, which is 0.

> 3.Associate the sum of the non-negative values in the list  numbers with the variable  sum .
>
> is it this:
>
> for numbers in  sum:
> if sum +=?
>
> I'm confused at #3 the most
>
Well, that's not valid Python.

What you want to do is to add each number from the list to the sum only 
if it's non-negative, i.e. greater than or equal to 0.

> i'm not doing it in python 3.2.3 it's called Myprogramminglab.
>
Have a look at Dive Into Python:
http://www.diveintopython.net/




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