在Python中跳过多行

Question

so I'm trying to skip over several rows from a .txt file and then creating a CSV file using csv reader. 18 rows need to be skipped. This gets the job done but I'm pretty sure there is an easy way of skipping 18 rows instead of using next() 18 times.

import csv
import os

my_file_name = os.path.abspath('LensBank.txt')
cleaned_file = "LensBankClean.csv"
with open(my_file_name, 'r', newline='') as infile, open(cleaned_file, 'w',newline='') as outfile:
    writer = csv.writer(outfile)
    cr =  csv.reader(infile, delimiter=',')

    next(cr)
    next(cr)
    next(cr)
    next(cr)
    next(cr)
    next(cr)
    next(cr)
    next(cr)
    next(cr)
    next(cr)
    next(cr)
    next(cr)
    next(cr)
    next(cr)
    next(cr)
    next(cr)
    next(cr)
    next(cr)
    writer.writerow(next(cr))

    for line in (r[:20] for r in cr):
     writer.writerow(line)

This works for me but how would I clean up the code to a much simpler version. Thanks!

Answer 1

Use range :

for skip in range(18):
    next(cr)

Answer 2

for i in range(18):
    next(cr)

Use a for loop. Or you can use itertools.dropwhile

for line in (r[:20] for i, r in itertools.dropwhile(lambda x: x[1] < 18 , enumerate(cr))):

Answer 3

That's strange that you used a for loop below, but haven't considered it for the same problem.

your code can easily be replaced by something like this

for i in range(18):
    next(cr)
writer.writerow(next(cr))

This will call next(cr) 18 times, and afterwards call writer.writerow

Answer 4

How about this,

import csv

# read a csv file into a list of lists
with open(in_file, 'r') as f_in:
    lists = [row for row in csv.reader(f_in, delimiter=',')] 

# write a list of lists to a csv file
with open(out_file, 'w') as f_out:
    writer = csv.writer(f_out)
    writer.writerows(lists[18:])    # skip the first 18 lines

---

As mentioned by @PatrickHaugh, the above solution is not effective for a large file. Below is the solution for a big files.

with open(in_file,'r') as f_in, open(out_file,'w') as f_out:
    # skip the first n lines
    for _ in range(18):
        next(f_in)
    for line in f_in:
        f_out.write(line)