How to write list of strings to file, adding newlines?

Question

def generator():
    nums = [\'09\', \'98\', \'87\', \'76\', \'65\', \'54\', \'43\']
    s_chars = [\'*\', \'&\', \'^\', \'%\', \'$\', \'#\', \'@\',]

    data =         


        

Answer 1

Pushing more work to the C layer with writelines and product:

from future_builtins import map  # Only do this on Python 2; makes map generator function
import itertools

def generator():
    nums = ['09', '98', '87', '76', '65', '54', '43']
    s_chars = ['*', '&', '^', '%', '$', '#', '@',]
    # Append newlines up front, to avoid doing the work len(nums) * len(s_chars) times
    # product will realize list from generator internally and discard values when done
    nums_newlined = (n + "\n" for s in nums)

    with open("list.txt", "w") as data:
        data.writelines(map(''.join, itertools.product(s_chars, nums_newlined)))

This produces the same effect as the nested loop, but does so with builtins implemented in C (in the CPython reference interpreter anyway), removing byte code execution overhead from the picture; this can dramatically improve performance, particularly for larger inputs, and unlike other solutions involving '\n'.join of the whole output into a single string to perform a single write call, it's iterating as it writes, so peak memory usage remains fixed instead of requiring you to realize the entire output in memory all at once in a single string.

Answer 2

Change

data.write(c+n)

to

data.write(c+n+'\n')

Answer 3

This one works for me

with open(fname,'wb') as f:
    for row in var:
        f.write(repr(row)+'\n')