Python Forum

how can I update CSV file ?

I have a list of name as a csv file, I read it and calculate the mean of them. finally I am going to add (name, mean) to the first csv file.

check csv module https://docs.python.org/3/library/csv.html

here is my csv code:

Quote:mandana,5,7,3,15
hamid,3,9,4,20,9,1,8,16,0,5,2,4,7,2,1
sina,19,10,19,6,8,14,3
sara,0,5,20,14
soheila,13,2,5,1,3,10,12,4,13,17,7,7
ali,1,9
sarvin,0,16,16,13,19,2,17,8

and I am going to calculate the mean of every list in csv and add the name and mean to the csv file.

import csv
from statistics import mean

import csv
from statistics import mean

with open ('grades.csv', 'r') as input_file_name:
    reader=csv.reader(input_file_name)
    lastrow=[]
    for row in reader:
        #print (row)
        name = row[0]
        these_grades=list()
        
        for grade in row[1:]:
            #print(grade)
            these_grades.append(int(grade))
            #print(name,grade,these_grades)
            
        print(name, mean(these_grades))
with open('grades.csv', 'w', newline='') as output_file_name:
    writer = csv.writer(output_file_name)
    writer.writerows(name )
    writer.writerows(mean )

because you want to overwrite the same file (is it a good idea?) you need to read the data from input file, calculate mean, store data in some data structure in memory and after you process all data - write to a file with same name.

import csv
from statistics import mean
 
with open ('grades.csv', 'r') as input_file:
    reader=csv.reader(input_file)
    data = []
    for row in reader:
        name = row[0]
        grades=[int(num) for num in row[1:]] # alternatively use: grades = map(int, row[1:])
        row.append(mean(grades))
        # alternatively use: row.append(f'{mean(grades):.2f}')
        data.append(row)

with open('grades.csv', 'w', newline='') as output_file_name:
    writer = csv.writer(output_file_name)
    writer.writerows(data)

thanks for your answer.
how can I update csv file with mean output results in new line.

actually the correct output result would be as below:

Quote:mandana,7.5
hamid,6.066666666666666
sina,11.285714285714286
sara,9.75
soheila,7.833333333333333
ali,5.0
sarvin,11.375

so i replaced the 11 line with below line:

 row.append(float(mean(grades)))

change lines 9-10 - instead of appending to row, just append to data new list with just name an mean

I dont get your point! can you explain more on the code?

and one more question, how can I make a dictionary from the name and the mean output.

name:keys and the mean:values

on line 9 I add mean to existing row - you don't need this
you need to create a list with two elements - name from row and mean
then append this new list to data

so you mean that I make a new row instead of appending the existing one with the new list?
the new list should be contain a name and mean?

import csv
from statistics import mean
  
with open ('grades.csv', 'r') as input_file:
    reader=csv.reader(input_file)
    data = []
    l2=[]
    for row in reader:
        name = row[0]
        grades=[int(num) for num in row[1:]] # alternatively use: grades = map(int, row[1:])
        l2.append(name)
        l2.append(float(mean(grades)))
        
        data.append(l2)

with open('grades.csv', 'w', newline='') as output_file_name:
    writer = csv.writer(output_file_name)
    writer.writerows(data)

the output repeat the result for every line !

you need to reset l2 for every row

import csv
from statistics import mean
   
with open ('grades.csv', 'r') as input_file:
    reader=csv.reader(input_file)
    data = []
    for row in reader:
        l2 = []
        name = row[0]
        grades=[int(num) for num in row[1:]] # alternatively use: grades = map(int, row[1:])
        l2.append(name)
        l2.append(float(mean(grades)))
        data.append(l2)
        # or just as a single line
        # data.append([row[0], float(mean(grades))])
 
with open('grades.csv', 'w', newline='') as output_file_name:
    writer = csv.writer(output_file_name)
    writer.writerows(data)