Avoiding empty line in writing process csv file

[go127a]

Hallo, I have done some calculation on csv file. However, the output csv, after writing process added one empty line at the end of results.

My question is how can I remove or avoid that line.

the code is here:

import csv
from statistics import mean
import itertools
from collections import OrderedDict


def calculate_average_of_averages(input_file_name, output_file_name):
    with open ('grades.csv', 'r') as input_file_name:
        reader=csv.reader(input_file_name)
        val1=[]
        key=list()
        data=[]
        for row in reader:
            l2 = []
            k = row[0] 
            grades=[int(num) for num in row[1:]]
            l2.append(float(mean(grades)))
            key.append(k) #making a name -key- list
            val1.append(l2) #making a value list
            value = list(itertools.chain.from_iterable(val1)) #making a simple list from list of list in value
            value=[float(i) for i in value] ##changing string to float in values
        dictionary = dict(zip(key, value))
        findic=OrderedDict(sorted(dictionary.items(), key=lambda t: t[1])) ##making a sorted list by OrderedDict
        
        lv=[]
        for item in findic.values():
                lv.append(item)
        data.append(float(mean(value)))
    with open('grades.csv', 'w', newline='') as output_file_name:
        writer = csv.writer(output_file_name)
        writer.writerows(map(lambda x: [x], data))
        output_file_name.close()

calculate_average_of_averages('input.csv','output.csv')

the correct output is:

8.401530612244898

but now I got the csv file like:

8.401530612244898
(this line is empty but exist)

[perfringo]

Maybe you could ask yourself a question - if you write-append to an existing csv file, where do you want your first line to be written? On the same line as last line in file or on a new line after last line?

[go127a]

its correct there is no problem with writing, the csv file should be rewrite by the results, but the problem is, I have two line in the output (one extra line, which is unnecessary)

the problem produced by 'writerows' i know that, but I can not find, how can I write the output except 'writerows'

csv writing process.
https://docs.python.org/3/library/csv.html

[perfringo]

Unfortunately you didn't ask the question I suggested.

How could (any) program know when and where row ends? There is newline at the end of every row. If you write a row it will end with newline. What will happen if there is newline at the end of last row?

[go127a]

I have used below code for writing, is it correct? (i mean is there any easier way?)

for item in data:
            
            dataf=str(item)
    with open('grades.csv', 'w', newline='') as output_file_name:
        
        output_file_name.write(dataf)
        output_file_name.close()