"IOError: [Errno 0] Error" error in Python

Question

I have a script that should append something to a file, but it is raising an error that I don't understand and not sure how it is being triggered.

Here is the code:

import re

num_words = "four kiddiewinks|four children|four kids"
words_list = num_words.split('|')

def append_2synonym(words_list, num_words):
    with open('test2 words.txt', 'a+') as f:
        read_f = f.read()
        patt = r'^' + words_list[0] + '\|'
        result = re.search(patt, read_f, re.MULTILINE)
        if result == None:
            f.write("\n" + num_words)
        else:
            print "\nNo match found in '2 words.txt' file"

append_2synonym(words_list, num_words)

Here is the contents of the 'test2 words.txt' file:

five kiddiewinks|five kids|five children
mobile phone|cell phone|cellular phone
stinky cheese|smelly cheese

Here is the full error I am getting:

Traceback (most recent call last):
  File "D:\Magic Briefcase\My Python Scripts\Spin Scripts\synonyms\testing2.py", line 16, in <module>
    append_2synonym(words_list, num_words)
  File "D:\Magic Briefcase\My Python Scripts\Spin Scripts\synonyms\testing2.py", line 12, in append_2synonym
    f.write("\n" + num_words)
IOError: [Errno 0] Error
[Finished in 0.1s with exit code 1]

Answer 1

Quoting answer from Python file operations, when switching between reading and writing on Windows, there must be an intervening fflush, fsetpos, fseek, or rewind operation.

Here is a possible fix:

import re

num_words = "four kiddiewinks|four children|four kids"
words_list = num_words.split('|')

def append_2synonym(words_list, num_words):
    with open('test2 words.txt', 'a+') as f:
        read_f = f.read()
        patt = r'^' + words_list[0] + '\|'
        result = re.search(patt, read_f, re.MULTILINE)
        if result == None:
            f.seek(0,2) # change is here !!
            f.write("\n" + num_words)
        else:
            print "\nNo match found in '2 words.txt' file"

append_2synonym(words_list, num_words)

In f.seek(0,2), 2 is the from_what argument. A from_what value of 0 measures from the beginning of the file, 1 uses the current file position, and 2 uses the end of the file as the reference point. from_what can be omitted and defaults to 0, using the beginning of the file as the reference point.