Raymond Hettinger <raymond.hettin...@gmail.com> added the comment:
I question those timings. Here's the results from a script I've been using for
many years:
$ python3.6 variable_access.py
0.065 read_local
0.068 read_nonlocal
0.179 read_global
0.236 read_builtin
0.267 read_classvar
0.392 read_instancevar
0.291 read_unboundmethod
0.383 read_boundmethod
0.077 write_local
0.069 write_nonlocal
0.240 write_global
1.154 write_classvar
0.540 write_instance
See the attached timing script: variable_access.py
Also, take a look at the underlying code:
#define GETLOCAL(i) (fastlocals[i])
TARGET(LOAD_FAST) {
PyObject *value = GETLOCAL(oparg);
if (value == NULL) {
...
}
Py_INCREF(value);
PUSH(value);
FAST_DISPATCH();
}
#define PyCell_GET(op) (((PyCellObject *)(op))->ob_ref)
TARGET(LOAD_DEREF) {
PyObject *cell = freevars[oparg];
PyObject *value = PyCell_GET(cell);
if (value == NULL) {
...
}
Py_INCREF(value);
PUSH(value);
DISPATCH();
}
You can see that the only difference is that LOAD_DEREF has one extra
indirection. That should be very cheap. In contrast, a LOAD_GLOBAL does a
lot more work. If this isn't evident in your timings, I suspect there is
something wrong with the timings.
----------
Added file: https://bugs.python.org/file47225/variable_access.py
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