[ python-Bugs-1119418 ] xrange() builtin accepts keyword arg silently

[SourceForge.net]

Bugs item #1119418, was opened at 2005-02-09 17:57
Message generated for change (Comment added) made by birkenfeld
You can respond by visiting: 
https://sourceforge.net/tracker/?func=detail&atid=105470&aid=1119418&group_id=5470

Please note that this message will contain a full copy of the comment thread,
including the initial issue submission, for this request,
not just the latest update.
Category: Python Library
Group: None
Status: Open
Resolution: None
Priority: 6
Submitted By: Martin Blais (blais)
Assigned to: Nobody/Anonymous (nobody)
Summary: xrange() builtin accepts keyword arg silently

Initial Comment:
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$ 


----------------------------------------------------------------------

>Comment By: Reinhold Birkenfeld (birkenfeld)
Date: 2005-06-09 23:04

Message:
Logged In: YES 
user_id=1188172

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.

----------------------------------------------------------------------

Comment By: Terry J. Reedy (tjreedy)
Date: 2005-02-16 23:21

Message:
Logged In: YES 
user_id=593130

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.

----------------------------------------------------------------------

You can respond by visiting: 
https://sourceforge.net/tracker/?func=detail&atid=105470&aid=1119418&group_id=5470