Calling ``xrange(10, 100, step=10)`` results in a
xrange(10, 100) iterator silently. In contrast,
``range(10, 100, step=10)`` raises an exception. See
test program below.
Two possible fixes:
1. fix xrange() so that it returns a xrange(10, 100,
10) iterator
2. make sure that xrange() raises an exception too.
#!/usr/bin/env python
def foo( min_, max_, step=1 ):
print min_, max_, step
print '===================='
foo(10, 100, 10)
foo(10, 100, step=10)
print '===================='
print xrange(10, 100, 10)
print xrange(10, 100, step=10)
print '===================='
print range(10, 100, 10)
print range(10, 100, step=10)
elbow:/usr/.../lib/python2.4$ /tmp/a.py
====================
10 100 10
10 100 10
====================
xrange(10, 100, 10)
xrange(10, 100)
====================
[10, 20, 30, 40, 50, 60, 70, 80, 90]
Traceback (most recent call last):
File "/tmp/a.py", line 16, in ?
print range(10, 100, step=10)
TypeError: range() takes no keyword arguments
> /tmp/a.py(16)?()
-> print range(10, 100, step=10)
(Pdb)
elbow:/usr/.../lib/python2.4$
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Functions coded in C generally do not take keyword
arguments. (Special coding is required to achieve
otherwise.) In 2.2, range and xrange both followed this rule:
>>> xrange(1,20,step=2)
Traceback (most recent call last):
File "<stdin>", line 1, in ?
TypeError: xrange() takes no keyword arguments
>>> range(1,20,step=2)
Traceback (most recent call last):
File "<stdin>", line 1, in ?
TypeError: range() takes no keyword arguments
So, removal of the error message by 2.4 seem to be a bug.
Surprise:
>>> str(object=1)
'1'
>>> str(i=2)
Traceback (most recent call last):
File "<stdin>", line 1, in ?
TypeError: 'i' is an invalid keyword argument for this function
There is nothing in the doc(Lib Ref) or doc string of str vs.
range and xrange that would lead me to expect this.
I looked around CVS a bit to see if the past or possible future
change was something simple, but I could not find source of
error message in bltinmodule.c, ceval.c, getargs.c,
rangeobject.c, or typeobject.c, so I will leave this to
someone else.
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I delved deeper into this, and it seems that the difference
is caused by range being a method (of bltinmodule, defined
as METH_VARARGS), while xrange is a constructor for a
rangeobject.
Such constructor functions get three arguments (the type
object, the args and the kw args), and when the kw args are
not checked like in str(), they can pass freely and are ignored.
I have attached a patch which changes the range object
constructor (xrange) to accept keyword arguments.
Other builtin types that need such a correction include
buffer, set, slice.
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xrange() needs to be kept closely parallel with range() .
Accordingly, it should not sprout keyword arguments.
For all of these, I think the solution is to raise a
TypeError when keyword arguments are supplied to
functions/types that don't handle them.
Encapsulate the logic in a new internal API function:
int
_PyArg_NoKeywords(char *funcname, PyObject *kwds)
{
if (kwds == NULL) return 1;
if (!PyDict_CheckExact(kwds)){
bad internal call
return 0;
}
if (PyDict_Size(kwds) == 0)
return 1;
set_exc_typeerror(funcname does not take kw args)
return 0;
}
Then go through the code finding all the type constructors
(grep for PyTypeObject) and add the error check if the kwds
arg is being ignored). For example:
range_new(PyTypeObject *type, PyObject *args, PyObject *kw)
{
if (!_PyArg_NoKeywords("xrange", kw))
return NULL;
. . .
Be sure to add test cases for every constructor that gets
changed. Also, go ahead an backport to Py2.4.2.
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Attaching a huge patch.
It introduces the function you described, and calls it in
the constructors of xrange, set, frozenset, buffer and slice.
Moreover, I found it to be necessary in objects in the
following modules:
- array (array)
- itertools (cycle, dropwhile, takewhile, islice, imap,
chain, ifilter, count, izip, repeat)
- operator (attrgetter, itemgetter)
- _random (Random)
- zipimport (zipimporter)
- collections (deque)
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