Red Hat Bugzilla – Bug 430991
Miss handling of errors by error handler in python
Last modified: 2008-01-31 10:42:18 EST
Description of problem: At the risk of starting an argument I find a bug in the functioning of the exception handling system try-except in python. An illustration will illlustrate the problem I see. Take the function: def plus(a,b): try: return(a+b) except TypeError: return None If I execute it as: plus(3,) the following is returned: Traceback (most recent call last): File "<stdin>", line 1, in <module> TypeError: plus() takes exactly 2 arguments (1 given) Now this is explained by some people by saying the error in arguments is found before the plus is executed so the TypeError is not found within the plus clause. I have taught interpreter writing and I know that the check of the arguments is done before the plus is executed in machine code. However, the exception handler is supposed to work on the python source level. A TypeError is generated on the python line plus(3,) and it should be caught. f8 has the samme problem. Version-Release number of selected component (if applicable): python-2.5-15.fc7 How reproducible: every time Steps to Reproduce: 1.execute: plus(3,) 2. 3. Actual results: Traceback (most recent call last): File "<stdin>", line 1, in <module> TypeError: plus() takes exactly 2 arguments (1 given) Expected results: no output Additional info: I assume this would happen with and error thrown.
1) The error is generated outside of the function. 2) The error is generated outside of the try block inside the function.
Created attachment 293526 [details] Show how to catch a TypeError within a function I'm not sure why you posted this here ... did you really expect Fedora to alter the python language? I'd also suggest that you go read the python language tutorials etc. quite a bit more, I've attached a "solution" to your problem written using normal python.
Well I will drop this buut I don't agree with the analysis in comment #1 above: Thhe error is generated when the function is taken by the interpreter to execute. I f we don't know what function we are executing we don't know how many arguments we are executing. The construct is: try <execution block> except TypeError action It is a python source construct. Its defineition is that is an error occurs in the <execution block> thenn the action will occur. This error is obviiously genrated in the try block and should be caught. The statemennt in 2) aboive is obviously fallacious from a python source perspective. I will drop this because it is bug is obviously part of the original python implimentation and no one wants to admit they were wrong all these years. I responded to comment #2 directly and commented on his demaning tone which he could get rid of. I own the Python Language Reference Manual Release 2.3 and I would claim the behavior of the python interpreter in Fedora is contrary to the decriptiion of its operation in that manual.