How to obtain the total numbers of rows from a CSV file in Python?

You need to count the number of rows:

row_count = sum(1 for row in fileObject)  # fileObject is your csv.reader

Using sum() with a generator expression makes for an efficient counter, avoiding storing the whole file in memory.

If you already read 2 rows to start with, then you need to add those 2 rows to your total; rows that have already been read are not being counted.

2018-10-29 EDIT

Thank you for the comments.

I tested several kinds of code to get the number of lines in a csv file in terms of speed. The best method is below.

with open(filename) as f:
    sum(1 for line in f)

Here is the code tested.

import timeit
import csv
import pandas as pd

filename = './sample_submission.csv'

def talktime(filename, funcname, func):
    print(f"# {funcname}")
    t = timeit.timeit(f'{funcname}("{filename}")', setup=f'from __main__ import {funcname}', number = 100) / 100
    print('Elapsed time : ', t)
    print('n = ', func(filename))
    print('\n')

def sum1forline(filename):
    with open(filename) as f:
        return sum(1 for line in f)
talktime(filename, 'sum1forline', sum1forline)

def lenopenreadlines(filename):
    with open(filename) as f:
        return len(f.readlines())
talktime(filename, 'lenopenreadlines', lenopenreadlines)

def lenpd(filename):
    return len(pd.read_csv(filename)) + 1
talktime(filename, 'lenpd', lenpd)

def csvreaderfor(filename):
    cnt = 0
    with open(filename) as f:
        cr = csv.reader(f)
        for row in cr:
            cnt += 1
    return cnt
talktime(filename, 'csvreaderfor', csvreaderfor)

def openenum(filename):
    cnt = 0
    with open(filename) as f:
        for i, line in enumerate(f,1):
            cnt += 1
    return cnt
talktime(filename, 'openenum', openenum)

The result was below.

# sum1forline
Elapsed time :  0.6327946722068599
n =  2528244


# lenopenreadlines
Elapsed time :  0.655304473598555
n =  2528244


# lenpd
Elapsed time :  0.7561274056295324
n =  2528244


# csvreaderfor
Elapsed time :  1.5571560935772661
n =  2528244


# openenum
Elapsed time :  0.773000013928679
n =  2528244

In conclusion, sum(1 for line in f) is fastest. But there might not be significant difference from len(f.readlines()).

sample_submission.csv is 30.2MB and has 31 million characters.