Writing a string.ishex function

[Aahz]

try: x = isinstance(s, int) and s or int(s, 0)
except ValueError: [handle invalid input]

Why aren't you using the ternary?

 

[Steven D'Aprano]

Don't use 'is', use '=='.

I beg to differ. In this case, since ishex is intended to return True or
False and not 1.0 or Decimal(0), the correct test for the purposes of
unit-testing is the identity test, not equality.

However, for the purposes of *displaying* the result, rather than saying:

print ishex('123') is True

one should obviously say:

print ishex('123') is True is True

No, wait, that should be:

print ishex('123') is True is True is True

No wait, this is better:

print ishex('123') is True is True is True is True

*wink*

Seriously, just say print ishex('123'). It already returns True or False,
you don't need to compare it to True or False to get a True or False
answer.

BTW, ishex('') should return False.

Only if you want to be inconsistent with other isFoo string functions:
False


Also, if ishex(s) returns True, then a reasonable person will expect that
calling int(s, 16) should succeed. But if s is the empty string, it will
fail.

 

[Wolfram Hinderer]

I raise you one character:

ishex2 = lambda s: not(set(s)-set(string.hexdigits))     # Yours
ishex3 = lambda s: not set(s)-set(string.hexdigits)      # Mine

I could actually go three better:

ishex3=lambda s:not set(s)-set(string.hexdigits)

ishex4=lambda s:not s.strip(string.hexdigits)

 

[MRAB]

ishex4=lambda s:not s.strip(string.hexdigits)

Doh!

 

[Vlastimil Brom]

That's true, but since you were the one that pointed out they were all
broken I would have thought your solution should actually work.

I'm sure you'll agree that a longer solution that works trumps any short
but broken solution.

ishex=lambda s:bool(re.match("[a-fA-F0-9]+$",s))
?
vbr

 

[MRAB]

That's true, but since you were the one that pointed out they were all
broken I would have thought your solution should actually work.

I'm sure you'll agree that a longer solution that works trumps any short
but broken solution.

I believe that the rules of the character-counting game don't require
correctness, only that it's no worse.

A real solution would use 'def', have a docstring, etc, of course.

 

[Steven D'Aprano]

Only if you want to be inconsistent with other isFoo string functions:

False

I said what???

Sorry MRAB, what I wrote there was obvious nonsense. I should be agreeing
with you, not disagreeing!

 

[Albert van der Horst]

Don't use 'is', use '=='.

BTW, ishex('') should return False.

You are very wrong. Not with the above statement, but
the very act of issuing a statement like that is wrong.

The OP didn't specify ishex().
In absence of a specification, border cases are not defined.

If the specification was:
any character of string s must be a hex character

then ishex('') should return True.

If the specification was:
the string must represent a hex number

then ishex('') should probably return False.

I can imagine a specification where it is appropriate to
throw an exception for an empty string.
This is also the safest thing to do, if there is the slightest
hesitation.

So the correct behaviour is:
"Please mister customer, what exactly did you have in mind?"

Groetjes Albert