Do you want to do something like this?

import csv
with open('large.csv','w') as f1:
    writer=csv.writer(f1, delimiter='\t',lineterminator='\n',)
    for i in range(1000000):
        row = [i + j*0.2 for j in range(i+1)]
        writer.writerow(row)

or also with the row/column headers:

import csv
with open('large.csv','w') as f1:
    writer=csv.writer(f1, delimiter='\t',lineterminator='\n',)
    writer.writerow([''] + range(1000000))
    for i in range(1000000):
        row = [i] + [i + j*0.2 for j in range(i+1)]
        writer.writerow(row)

The latter returns the following file (I have replaced 1000000 with 10):

        0       1       2       3       4       5       6       7       8       9
0       0.0
1       1.0     1.2
2       2.0     2.2     2.4
3       3.0     3.2     3.4     3.6
4       4.0     4.2     4.4     4.6     4.8
5       5.0     5.2     5.4     5.6     5.8     6.0
6       6.0     6.2     6.4     6.6     6.8     7.0     7.2
7       7.0     7.2     7.4     7.6     7.8     8.0     8.2     8.4
8       8.0     8.2     8.4     8.6     8.8     9.0     9.2     9.4     9.6
9       9.0     9.2     9.4     9.6     9.8     10.0    10.2    10.4    10.6    10.8

import csv
with open("sample.csv", "w") as csvFile:
    fieldnames = ['Item Name']
    writer = csv.DictWriter(csvFile, fieldnames=fieldnames)
    writer.writeheader()

    for item in list:
        info  = inspect.getmembers(item)
        name = info[0]

        writer.writerow({'Item Name': name })

import csv
import pandas as pd

with open('Remarks_Drug.csv', newline='', encoding ='utf-8') as myFile:
    reader = csv.reader(myFile)
    mydrug = []
    for row in reader:
        product = row[0].lower()
        #print('K---'+ product)
        filename = row[1]
        product_patterns = ', '.join([i.split("+")[0].strip() for i in product.split(",")])
        mydrug.append([product_patterns, filename])

#     print(mydrug)

    df = pd.DataFrame(mydrug, columns=['product_patterns', 'filename'])
    print(df)
    df.to_csv('drug_output100.csv', sep=',', index=False)

This utilizes pandas library. If you're to deal with large csv files using pandas will be handy and efficient in terms of performance and memory. This is just an alternative solution for the above.

open your csv file once, and write one line per iteration, and no need for so many variables:

with open('test.csv', 'w') as csvFile:
   writer=csv.writer(csvFile, delimiter=',', quotechar='|', quoting=csv.QUOTE_MINIMAL, lineterminator='\n')

   for i in list_people:
       info = inspect.getmembers(i)
       writer.writerow(info[1:3])

or completely replace the for loop by writerows using a generator comprehension, that will be even faster:

writer.writerows(inspect.getmembers(i)[1:3] for i in list_people)

Every time you open the file in w mode, it will overwrite everything that was there. You should open the file one time, then loop over calls to writerow like:

with open(str(out_dir)+str(nme[0])+'.csv','w') as f1:
    writer=csv.writer(f1, delimiter=',')#lineterminator='\n',
    for i in np.arange(0,9):
        row = data[i]
        writer.writerow(row)

instead of reopening the file each iteration through the for loop

Although for this task you don't need it, I would take advantage of standard library modules when you can, like csv. Try something like this,

import os
import csv

csvfile = open('outputFileName.csv', 'wb')
writer = csv.writer(csvfile)

for filename in os.listdir('/'): # or C:\\ if on Windows
    writer.writerow([filename, len(filename)])

csvfile.close()

You would create the csv row as a loop (or using list comprehension) I will show the explicit loop for ease of reading and you can change it to a single list comprehension line yourself.

row = []
for n in deats:
  row.append(n)

Now you have row ready to write to the .csv file using csv.Writer()

Leaving the with block closes with file. Therefore, the new_file function just opens and immediately closes a file.

You could do somthing like the following:

import csv

rowCounter     = 0
fileCounter    = 0
List_A         = ['a', 'b', 'c', 'd', 'e', 'f', 'g']
List_B         = ['a', 'b', 'c', 'd', 'e', 'f', 'g']
List_C         = ['a', 'b', 'c', 'd', 'e', 'f', 'g']

# create file handle
csvfile = open('file-' + str(fileCounter) + '.csv', 'w')

rowWriter = csv.writer(csvfile, delimiter=',', quoting=csv.QUOTE_NONE)

for word1 in List_A:
    for word2 in List_B:
        for word3 in List_C:
            sentence = word1 + word2 + word3
            rowWriter.writerow ([sentence])

            rowCounter += 1

            if rowCounter == 100:
                # close current filehandle
                csvfile.close()
                fileCounter += 1
                # open new file
                csvfile =  open('file-' + str(fileCounter) + '.csv', 'w')
                rowWriter = csv.writer(csvfile, delimiter=',', quoting=csv.QUOTE_NONE)
                rowCounter = 0

# close file
csvfile.close()

or with defining a function:

import csv

rowCounter     = 0
fileCounter    = 0
List_A         = ['a', 'b', 'c', 'd', 'e', 'f', 'g']
List_B         = ['a', 'b', 'c', 'd', 'e', 'f', 'g']
List_C         = ['a', 'b', 'c', 'd', 'e', 'f', 'g']

def new_writer( csvfile, counter ):
     if csvfile: 
         csvfile.close()

     # open new file
     csvfile =  open('file-' + str(counter) + '.csv', 'w')
     rowWriter = csv.writer(csvfile, delimiter=',', quoting=csv.QUOTE_NONE)

     counter += 1

     return rowWriter,csvfile,counter

rowWriter, csvFile, fileCounter = new_writer( None, fileCounter )

for word1 in List_A:
    for word2 in List_B:
        for word3 in List_C:
            sentence = word1 + word2 + word3
            rowWriter.writerow ([sentence])

            rowCounter += 1

            if rowCounter == 100:
                # close current file and open a new one
                rowWriter, csvfile, counter =  new_writer( csvfile, fileCounter )         
                rowCounter = 0

# close file
csvFile.close()

Structure the code so that you're opening the file outside of the loop:

with open('Products.csv', mode='w') as file_in:
    writers = csv.writer(writers)
    for item in soup.select('.s-item'):
        # etc...

What's happening is that each iteration of the loop, you're re-opening the file, and with mode='w' you're overwriting the file contents.

Put the

with open('results.csv', 'w') as csvfile:
    writer = csv.writer(csvfile)
    writer.writerow(['company', 'followers', 'result'])

outside (above) the loop, and call writer.writerow inside the loop. The loop must be inside the with block.

You are encountering the error because it is re-writing a csv for every iteration in your loop. You should move the with open() statement outside of your loop block.