Python – “IOError: [Errno 0] Error”. What is Triggering This Error In My Code?

Python/programming newbie here.

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]

Any help appreciated
Cheers
Darren

Best answer

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.