What could possibly go wrong?
The only problem is, much code can become the same, not because of copying but because of using the same methods.
If you create a python script that for example fetches an image by running an open API's functions in some places, it is highly possible that a closed project which also uses said open API could have a function that is identical as it's performing the same task with the same API.
There are many situations where identical code can appear when performing the same task. Doesn't always mean it's been copied.
Then of course, there are patent laws which prevent you from coding something to do something which some big corp numpty has patented.
For example, our EPOS system synchronizes with our website (Selling in store notifies the website server, server adjusts stock levels online and visa versa, keeps a complete log and totals for each day including who sold what etc, don't panic though, the EPOS system uses an stunnel to connect to the web server directly! None of it flies over in plain text!), the whole thing is custom (which is why the EPOS can run Linux, keeping the company Linux only, this way the EPOS software gets to stay native instead of inside internet explorer or something :P). The downside of this is of course the issue that if the store looses internet connectivity it has to revert to an "offline mode" which has no sync.
I mention this because the methods I use are almost certainly copyrighted somewhere. But I did it myself and I'm not too fussed about copyright, I didn't take anyone else's code or copy anything. I just built it to task.
Should I be considered a pirate/thief for doing it myself instead of paying some big corp? In the eyes of the law almost certainly!
- Anon because of confession.