Python Pandas DataFrame stops working after certain row

Question

I have a few programs where I would like to import data from CSV files, do some calculations and then output to a new CSV.

However, when I run the following code and the input file is larger than ~ 100 rows, the code stops working after row 29 and then resumes at some point later on.

Note, the ".. .." you see in the output are in fact in the output file. This is not a placeholder. The dataframe creation seems to stop at 29 and then resumewith 156. In between nothing but the one row with "..".

If I use an input file with say 40 rows only, then those work correctly.

Can someone help me out here? Not sure where the problem is.

Thank you all for your help

Alex

import csv
import pandas as pd
from tkinter import *
from tkinter import filedialog as fd

root = Tk()

ImportFile = fd.askopenfilename()
with open(ImportFile, newline='') as csvfile:
    reader = csv.DictReader(csvfile)
    df = pd.DataFrame(columns=["ColA", "ColB", "ColC", "ColD"])
    for row in reader:
        global ColA
        ColA = float(row['ColA'])
        global ColB
        ColB = float(row['ColB'])
        global ColC
        ColC = float(row['ColC'])
        
        header = ['ColA', 'ColB', 'ColC', 'ColD']
        data = [ColA, ColB, ColC, "0"]
        df.loc[len(df)] = data
        print(df)
    f = open("batchoutput.csv", "w", encoding="UTF-8")
    f.write(str(df))
    f.close()

root.destroy()

Output:

     ColA   ColB    ColC ColD
0    10.0   10.0  164.00    0
1    10.0   11.0  176.00    0
2    10.0   11.0  171.00    0
3    10.0  617.0  183.00    0
4    10.0   12.0   18.00    0
5    10.0  618.0  182.00    0
6    10.0  607.0  175.00    0
7    10.0  615.0  184.00    0
8    10.0  616.0  187.00    0
9    10.0  614.0   18.00    0
10   10.0  616.0   19.00    0
11   10.0  616.0   18.00    0
12   10.0  865.0  168.00    0
13   10.0  869.0  134.00    0
14   10.0  868.0  138.00    0
15   10.0   10.0  164.00    0
16   10.0   11.0  176.00    0
17   10.0   11.0  171.00    0
18   10.0  617.0  183.00    0
19   10.0   12.0   18.00    0
20   10.0  618.0  182.00    0
21   10.0  607.0  175.00    0
22   10.0  615.0  184.00    0
23   10.0  616.0  187.00    0
24   10.0  614.0   18.00    0
25   10.0  616.0   19.00    0
26   10.0  616.0   18.00    0
27   10.0   11.0  199.00    0
28   10.0  618.0  188.00    0
29   10.0   10.0  198.00    0
..    ...    ...     ...  ...
157  10.0  618.0  188.00    0
158  10.0   10.0  198.00    0
159  10.0   11.0    3.07    0
160  10.0  617.0  151.00    0
161  10.0  619.0  156.00    0
162  10.0  616.0   17.00    0
163  10.0  619.0   16.00    0
164  10.0   13.0  153.00    0
165  10.0  618.0   11.00    0
166  10.0  616.0   17.00    0
167  10.0  614.0  167.00    0
168  10.0  615.0  171.00    0
169  10.0  616.0  185.00    0
170  10.0  618.0  189.00    0
171  10.0   11.0  174.00    0
172  10.0  861.0   11.00    0
173  10.0  856.0  174.00    0
174  10.0  863.0  172.00    0
175  10.0   81.0  173.00    0
176  10.0  861.0  169.00    0
177  10.0   81.0   17.00    0
178  10.0  864.0  169.00    0
179  10.0  863.0  172.00    0
180  10.0  870.0  182.00    0
181  10.0  864.0   18.00    0
182  10.0  863.0   18.00    0
183  10.0   81.0   17.00    0
184  10.0  865.0  168.00    0
185  10.0  869.0  134.00    0
186  10.0  868.0  138.00    0

[187 rows x 4 columns]