How to get "17"<"9" to create an error?

Question

Is there any good way to get rid of the possibility of application to strings of the greater smaller comparison operators and the min max functions? Like aliasing? The problem is that the behaviour is just not useful to me.

So that '17'<'9' gives an error and not the (for me) beautifully useless and confusing results it does now? This has caused trouble for me multiple times in the form of:

'17'<'9'
True

I mean i could alias them to throw an exception if strings are used I guess but I would like a canonical way if that exsists.

Please don't explain lexicographical ordering or int() to me...

You mean you don't want to use comparison operators to compare strings? — thefourtheye, Jul 12 '16 at 07:07
I ment that i don't want string comparisons to be possible like that and to get an error instead. — Kuhlambo, Jul 12 '16 at 07:15
No. Instead, don't keep values in string form if you want to compare them numerically. — BrenBarn, Jul 12 '16 at 07:15
Strings have ordering, otherwise you couldn't *sort* them. It is that order that informs the `<` and `>` operators. You can't just disable them for strings, no. — Martijn Pieters, Jul 12 '16 at 07:19
Also, the results are in no way "undefined". They're defined by the lexicographic order of the characters in the strings. — BrenBarn, Jul 12 '16 at 07:19
`hey` sorts before `ho` because `e` sorts before `o` in the alphabet. Strings are compared lexicographically. — Martijn Pieters, Jul 12 '16 at 07:20
Why don't you check the type first then? `isinstance(x, str)` — , Jul 12 '16 at 07:36
What you want to do is either changing the interpreter or [this](http://stackoverflow.com/questions/4698493/can-i-add-custom-methods-attributes-to-built-in-python-types) and I dont think you want to redefine the string class — , Jul 12 '16 at 07:57

score 1 · Answer 1 · answered Jul 12 '16 at 08:02

I'll risk flames... :-) What you can do is create a new string class, almost identical to the native one, but with providing a new set of equality functions.

For example, just overriding the > operation:

class newstr(str):  # Inheriting str class

    def __gt__(self, s):
        raise RuntimeError("This is an error")

Now

In [1]: a = newstr('17')
In [2]: b = newstr('9')

In [3]: a<b
Out[3]: True   #since we haven't override __lt__

In [4]: a>b
Traceback (most recent call last):

  File "<ipython-input-64-f269bf469c37>", line 1, in <module>
    a>b

  File ".../untitled0.py", line 6, in __gt__
    raise RuntimeError("This is an error")

RuntimeError: This is an error

Use __lt__ and __eq__ for other equality conditions.

How to get "17"<"9" to create an error?

1 Answers1