Loop using to_csv only printing last file (Python)

Question

I am trying to load a number of csv files from a folder, use a function that calculates missing values on each file, then saves new csv files containing the output. When I edit the script to print the output, I get the expected result. However, the loop only ever saves the last file to the directory. The code I am using is:

from pathlib import Path
import pandas as pd
import os
import glob

files = glob("C:/Users/61437/Desktop/test_folder/*.csv") # get all csv's from folder

n = 0

for file in files:
    print(file)
    df = pd.read_csv(file, index_col = False)
    d = calc_missing_prices(df) # calc_missing_prices is a user defined function
    print(d)
    d.to_csv(r'C:\Users\61437\Desktop\test_folder\derived_files\derived_{}.csv'.format(n+1), index = False)

The print() command returns the expected output, which for my data is:

C:/Users/61437/Desktop/test_folder\file1.csv
   V_150  V_200  V_300  V_375  V_500  V_750  V_1000
0   3.00   2.75   4.50   6.03   8.35  12.07   15.00
1   2.32   3.09   4.63   5.00   9.75  12.50   12.25
2   1.85   2.47   3.70   4.62   6.17   9.25   12.33
3   1.75   2.00   4.06   6.50   6.78  10.16   15.20
C:/Users/61437/Desktop/test_folder\file2.csv
   V_300  V_375  V_500  V_750  V_1000
0   4.00   4.50   6.06   9.08   11.00
1   3.77   5.00   6.50   8.50   12.56
2   3.00   3.66   4.88   7.31    9.50
C:/Users/61437/Desktop/test_folder\file3.csv
   V_500  V_750  V_1000
0   5.50   8.25   11.00
1   6.50   8.50   12.17
2   4.75   7.12    9.50

However the only saved csv file is 'derived_1.csv' which contains the output from file3.csv

What am I doing that is preventing all three files from being created?

Answer 1

You are not incrementing n inside the loop. Your data gets stored in the file derived_1.csv , which is overwritten on every iteration. Once the for loop finishes executing, only the last csv will be saved.

Include the line n += 1 inside the for loop to increment it by 1 on every iteration.