Write and read a list from file

Question

This is a slightly weird request but I am looking for a way to write a list to file and then read it back some other time   I have no way to remake the lists so that they are correctly formed formatted as the example below shows   My lists have data like the following   test data here this is one group     test data here this is another group

User · Answer

As long as your file has consistent formatting (i.e. line-breaks), this is easy with just basic file IO and string operations:

with open('my_file.txt', 'rU') as in_file:
    data = in_file.read().split('\n')

That will store your data file as a list of items, one per line. To then put it into a file, you would do the opposite:

with open('new_file.txt', 'w') as out_file:
    out_file.write('\n'.join(data)) # This will create a string with all of the items in data separated by new-line characters

Hopefully that fits what you're looking for.

User · Answer

Let s define a list first   lst  1 2 3    You can directly write your list to a file   f open  filename txt   w   f write str lst   f close     To read your list from text file first you read the file and store in a variable   f open  filename txt   r   lst f read   f close     The type of variable lst is of course string  You can convert this string into array using eval function   lst eval lst

User · Answer

If you don t need it to be human-readable editable  the easiest solution is to just use pickle   To write   with open the filename   wb   as f      pickle dump my list  f    To read   with open the filename   rb   as f      my list   pickle load f      If you do need them to be human-readable  we need more information   If my list is guaranteed to be a list of strings with no embedded newlines  just write them one per line   with open the filename   w   as f      for s in my list          f write s     n    with open the filename   r   as f      my list    line rstrip   n   for line in f      If they re Unicode strings rather than byte strings  you ll want to encode them   Or  worse  if they re byte strings  but not necessarily in the same encoding as your system default    If they might have newlines  or non-printable characters  etc   you can use escaping or quoting  Python has a variety of different kinds of escaping built into the stdlib   Let s use unicode-escape here to solve both of the above problems at once   with open the filename   w   as f      for s in my list          f write  s   u  n   encode  unicode-escape     with open the filename   r   as f      my list    line decode  unicode-escape   rstrip u  n   for line in f      You can also use the 3 x-style solution in 2 x  with either the codecs module or the io module    import io  with io open the filename   w   encoding  unicode-escape   as f      f writelines line   u  n  for line in my list   with open the filename   r   as f      my list    line rstrip u  n   for line in f      TOOWTDI  so which is the one obvious way  It depends    For the short version  if you need to work with Python versions before 2 6  use codecs  if not  use io

[python] Write and read a list from file

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