OS Module: Does the file content contains string x? (Python 3.4)

Question

If I get the content of a file with ret = os.read(fd, os.path.getsize(file)), how do I check if ret contains a specific string, for example "hello world"?

An answer on here was simply if "hello world" not in ret:, but this does not work anymore in python 3.4, apparently (Because of mixing bytes with unicode or something). How do I do this now?

Any particular reason you're using `os.read` and file descriptors? — Jon Clements, May 10 '15 at 15:57
`if b"hello world" not in ret:` (note the `b` before the string). But why are you using `os.read()`? — Andrea Corbellini, May 10 '15 at 15:58
http://stackoverflow.com/a/606199/758446 will help you get your bytestring to a string. — BlackVegetable, May 10 '15 at 15:58
@JonClements I never used Python and just googled how to read a file, this method came up — Fly, May 10 '15 at 15:58
Ah, google "python file I/O" to get better results. That isn't the best or most common way to read from a file. — BlackVegetable, May 10 '15 at 15:59
@Fly okay... best to avoid it then.... use `ret = open('filename').read()` insted — Jon Clements, May 10 '15 at 15:59
@AndreaCorbellini Thanks, works! I'm using os module because I never used python and just googled how to read a file, and this method came up. — Fly, May 10 '15 at 15:59
https://docs.python.org/dev/tutorial/inputoutput.html#reading-and-writing-files — Andrea Corbellini, May 10 '15 at 16:00
@AndreaCorbellini Shall I answer my own question or do you want to write a "real" answer so I can accept it? — Fly, May 10 '15 at 16:29

score 1 · Accepted Answer · answered May 10 '15 at 16:32

The easy fix is to prefix the string with b, so that it is treated as a byte string:

if b"hello world" not in ret:

However I strongly recommend you to use the builtin open() and file objects, as described on the Python I/O tutorial.

On Python 3, strings returned by file objects are always unicode strings by default, so that you don't have to bother about byte strings and encodings.

Here is a working example:

with open(file_name) as f:
    file_content = f.read()

if 'hello world' not in file_content:
    ...

OS Module: Does the file content contains string x? (Python 3.4)

1 Answers1