why not yield not return give me the right answer in my code about average

Question

I am new in python and I wanna calculate averages of grades for a student class with this:

from statistics import mean
import csv
def calculate_averages(input_file_name, output_file_name):
    with open('D:\\p3\\grades.csv', 'r') as f:
        f = csv.reader(f)
        namelist=[]
        averagelist=[]
        for row in f:
            name = row[0]
            scores = row[1:]
            scores = list(map(int, scores))
            average = mean(scores)
            namelist = name
            averagelist=average
            print(namelist, averagelist)
    yield namelist, averagelist
print(calculate_averages('namelist', 'averagelist'))

I put print n the code to see if where the problem is: when I use return it gives me :

mahtaab 15.5
Reza 14
Mahyar 15.5
Shamim 17.166666666666668
Milad 13.5
('Milad', 13.5)

when I use yield it returns:

<generator object calculate_averages at 0x0000019FB6474BA0>

what is the problem?

(-1) because it is unclear what your question is. Do you want to calculate an average (have a look at `numpy.mean()` ) or do you want to know the difference between `yield` and `return`? (the first creates a generator object, which calculates the results on the fly; the latter turns your code into a normal function) — max, Jan 27 '20 at 07:59

score 0 · Answer 1 · answered Jan 27 '20 at 07:57

0

You can perform print(list(calculate_averages('namelist', 'averagelist'))) or print([i for i in calculate_averages('namelist', 'averagelist')])

answered Jan 27 '20 at 07:57

ruslan_krivoshein

303
5
19

ezdazuzena · Answer 2 · 2020-01-27T08:57:59.220

0

You are printing the generator object. In order to get the list ("content" of the generator) you'll have to iterate over it, for instance by casting it to a list:

>>> def bla():
...     for i in range(10):
...         yield i
... 
>>> print(bla())
<generator object bla at 0x7f1cd1a770f8>
>>> print(list(bla()))
[0, 1, 2, 3, 4, 5, 6, 7, 8, 9]

Have a look at this answer to understand generators: https://stackoverflow.com/a/1756156/11164958

Or at https://docs.python.org/3/glossary.html#term-generator:

A function which returns a generator iterator. It looks like a normal function except that it contains yield expressions for producing a series of values usable in a for-loop or that can be retrieved one at a time with the next() function.

edited Jan 27 '20 at 08:57

answered Jan 27 '20 at 08:06

ezdazuzena

6,120
6
41
71

the list yields the same, just the last one in my csv file – Mahtaab Phy Jan 27 '20 at 08:10
1

@MahtaabPhy you might need to move the `yield` inside your for loop, if this is what you want. Is not clear from your question – ezdazuzena Jan 27 '20 at 08:12
it returns just the last line in csv file not a list of students' name and their average – Mahtaab Phy Jan 27 '20 at 08:16
`yield` must be at the same level as `print` – ezdazuzena Jan 27 '20 at 08:25
noooo It needed an empty line between my function and print comman, it woorkkss thank you !! by your comment I reach this solution – Mahtaab Phy Jan 27 '20 at 08:32

why not yield not return give me the right answer in my code about average

2 Answers2