4.4 Interpreting Error Messages

One of Python’s unique features is the level of source location information it provides in error messages. The error messages contain a lot of detail in a terse format, to they may be confusing at first. Error messages will be illustrated using this example program:

(defmacro zoq (x)
  `(roq (ploq (+ ,x 3))))

(defun foo (y)
  (declare (symbol y))
  (zoq y))

The main problem with this program is that it is trying to add 3 to a symbol. Note also that the functions roq and ploq aren’t defined anywhere.

• The Parts of the Error Message
• The Original and Actual Source
• The Processing Path
• Error Severity
• Errors During Macroexpansion
• Read Errors
• Error Message Parameterization