Once you've saved a file with a file extension (i.e. something.py), CS50 IDE's text editor will detect syntax errors in your code. Sometimes the error will be on the same line asand other times it will be the line after. Keep this in mind when you're debugging your code.
Fix syntax errors as they appear. Don't write lines and lines of code without testing to see if your program works. It will cost you more time in the long run.
Cloud9 detects a syntax error on the same line as the syntax error.
Error in line 12
Cloud9 detects a syntax error as the line after the syntax error.
Error in line 21
Similarly, if run the file in the Terminal, Python will give you a similar error message. Remember, the error is on that line or the previous line.