Unexpected Behaviour when using the Built-In 'open' Function

[aba-hb]

Bug report

Bug description:

Hi!

When calling the 'open' function with a path that contains invalid symbols inside the file name, e.g. a colon, the function will truncate that path, proceed to create the file, but not write any contents to it.
What I expected to happen is that an exception is being raised and no file is created.

I don't know if this is intended behaviour and I couldn't find something about this in neither the documentation (https://docs.python.org/3/library/functions.html#open) or the PEP website.

Can somebody confirm/deny that this is a bug?

Minimal reproducible example

def main():
    from os import path
    basePath = path.dirname(__file__)
    filePath = path.join(basePath, "invalid:symbols.txt")
    fileContent = "hello world that is probably not being written to file"
    with open(filePath, "w", encoding="utf-8") as file:
        file.write(fileContent)


if __name__ == "__main__":
    main()

The above snippet results in an empty file called invalid.txt to be created.

I hope that this isn't a duplicate, I tried searching for a similar unclosed issue but couldn't find any.
In case this is expected behaviour, it would be great if it'd be mentioned in the documentation. 🥰

EDIT: Fixed the wrong file name, sorry

CPython versions tested on:

3.12, 3.13

Operating systems tested on:

Windows

[ronaldoussoren]

Is the empty file named "invalid"? I'd expect that trying to read from the same path (e.g. "invalid:symbols.txt") would give you the contents you wrote earlier.

This is due to the "NTFS streams" feature on Window, where files on NTFS can have more than one data stream.

[aba-hb]

Yes, sorry, it's indeed "invalid.txt" and not "input.txt", somehow I messed up the example 😓

I didn't know about NTFS, but now I understand what's going on, this is by zero means a Python issue but rather a Windows feature that I missed..

Thank you for the reply and clarification! 👍🏻