I recently encountered a strange issue with my Python code that's making an API call. The code was functioning perfectly until a few hours ago, but now it suddenly returns an error stating that the input is invalid, even though I haven't changed anything. Other parts of the code calling the same API are fine, which rules out any issues with the API itself. I decided to run an older version of my Python code that had previously worked, and that ran without any problems. After comparing the API call line between the old and new code, they seemed identical. To resolve the issue, I copied the line from the old code and replaced the one in the new code, and it worked again! This leads me to believe a hidden character got into the new code somehow. I'm curious: what kind of hidden characters could cause this? Why didn't my IDE, PyCharm, show these hidden characters? Don't most text editors display all hidden characters, excluding just new line and carriage return characters? What are the best practices for preventing and handling such hidden character issues?
5 Answers
I've noticed issues where copied text from web pages uses opening and closing quotes instead of standard ones, which can result in syntax errors that are hard to spot. Just double-check your quotes!
If you’re on Windows, Notepad++ has a handy feature for revealing non-visible characters. You can find it under View -> Characters -> Show all characters. It can help troubleshoot these issues, though it’s not likely that a zero-width character is the culprit.
From my experience, hidden characters usually come from typos we overlook. I highly recommend using git; you can check the history with 'git blame' to see when a line was changed and by whom. This is super handy for tracking down those sneaky characters. If you're using something like GitLab, they have a feature that's easy to use for that too!
You should definitely learn to use a *diff* tool. Often these hidden issues are simple, like typographic versus straight quotes. A good diff tool will highlight what’s wrong in your code. Keep in mind that most IDEs won't show hidden characters.
Most IDEs don’t display zero-width characters, such as `u200b` or `ufeff`, since they are technically valid in Unicode. This can make your code look normal while still causing issues.

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