Status: Accepted
Owner: nicolas.pourcelot
CC: Vinzent.Steinberg, asmeurer, smichr
Labels: Type-Defect Priority-Medium
New issue 2125 by nicolas.pourcelot: Using Integers as python slices.
http://code.google.com/p/sympy/issues/detail?id=2125
I'd like to be able to use sympy Integers everywhere python integers are
allowed, and so, to implement the following:
In [1]: a = Integer(2)
In [2]: "hello"[a:]
Out[2]: llo
For now, this raises an error:
"hello"[Integer(2):]
Traceback (most recent call last):
File "<input>", line 1, in <module>
TypeError: slice indices must be integers or None or have an __index__
method
However, adding an __index__ method to Integer makes the following work:
In [4]: a=Integer(2)
In [5]: a*'1'
Out[5]: 11
And there is a test in sympy/core/tests/test_expr.py preventing this
behavior:
# basic sympy objects
basic_objs = [
Rational(2),
Real("1.3"),
x,
y,
pow(x,y)*y,
]
def test_basic_nostr():
for obj in basic_objs:
for op in ['+','-','*','/','**']:
raises(TypeError, "obj %s '1'" % op)
Why shouldn't that be allowed ?
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