python - Loop over rows of csv.DictReader more than once

Question

I open a file and read it with csv.DictReader. I iterate over it twice, but the second time nothing is printed. Why is this, and how can I make it work?

with open('MySpreadsheet.csv', 'rU') as wb:
    reader = csv.DictReader(wb, dialect=csv.excel)
    for row in reader:
        print row

    for row in reader:
        print 'XXXXX'

# XXXXX is not printed

Answer 1

You read the entire file the first time you iterated, so there is nothing left to read the second time. Since you don't appear to be using the csv data the second time, it would be simpler to count the number of rows and just iterate over that range the second time.

import csv
from itertools import count

with open('MySpreadsheet.csv', 'rU') as f:
    reader = csv.DictReader(f, dialect=csv.excel)
    row_count = count(1)

    for row in reader:
        next(count)
        print(row)

for i in range(row_count):
    print('Stack Overflow')

If you need to iterate over the raw csv data again, it's simple to open the file again. Most likely, you should be iterating over some data you stored the first time, rather than reading the file again.

with open('MySpreadsheet.csv', 'rU') as f:
    reader = csv.DictReader(f, dialect=csv.excel)

    for row in reader:
        print(row)

with open('MySpreadsheet.csv', 'rU') as f:
    reader = csv.DictReader(f, dialect=csv.excel)

    for row in reader:
        print('Stack Overflow')

If you don't want to open the file again, you can seek to the beginning, skip the header, and iterate again.

with open('MySpreadsheet.csv', 'rU') as f:
    reader = csv.DictReader(f, dialect=csv.excel)

    for row in reader:
        print(row)

    f.seek(0)
    next(reader)

    for row in reader:
        print('Stack Overflow')