Issue 11655: map() must not swallow exceptions from PyObject_GetIter (original) (raw)

The built-in function map() currently swallows any exception that might have occured while trying to get an iterator from any parameter. This produces unexpected behaviour for applications that require a certain type of exception to be raised when iter() is called on their objects.

From 24179f82b7de, inside map_new():

973 /* Get iterator. */ 974 curseq = PyTuple_GetItem(args, i+1); 975 sqp->it = PyObject_GetIter(curseq); 976 if (sqp->it == NULL) { 977 static char errmsg[] = 978 "argument %d to map() must support iteration"; 979 char errbuf[sizeof(errmsg) + 25]; 980 PyOS_snprintf(errbuf, sizeof(errbuf), errmsg, i+2); 981 PyErr_SetString(PyExc_TypeError, errbuf); 982 goto Fail_2; 983 }

We must check if there has been any other kind of exception already being set when returning from PyObject_GetIter before setting PyExc_TypeError in line 981. If there is none, it is ok to raise a TypeError; any other exception must be passed on.

For example: raising TooManyCacheMissesException in iter() causes map(foobar, myobject) to raise TypeError instead of TooManyCacheMissesException.

Workaround: use map(foobar, iter(myobject)). The explicit call to iter will either produce an iterator object (which returns self to map()) or raises the correct exception.

Python 3 is not affected as map_new() does not throw it's own TypeError in case PyObject_GetIter() fails.