Batteries! creative solution for Surjection Strings by veky - python coding challenges

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Batteries! solution in Creative category for Surjection Strings by veky

isometric_strings = lambda a, b: a.translate(str.maketrans(a, b)) == b

Jan. 15, 2019

Comments:

Ylliw on Jan. 22, 2019, 10:23 a.m.
That look easy like this...

veky on Jan. 22, 2019, 10:44 a.m.
If antigravity is easy, this is piece of cake. :-P

juestr on May 30, 2019, 11:40 a.m.
I thought about this too and it works atm, but maketrans is not defined for the case of an inconsistent mapping. Future or other python implementations may raise an Exception without warning, and I'd rather call it creative for that reason. <a href="https://docs.python.org/3/library/stdtypes.html?highlight=str">https://docs.python.org/3/library/stdtypes.html?highlight=str</a>#str.maketrans

veky on May 30, 2019, 1 p.m.
Sorry, but I don't see that in the link you provided. It's as if you say a Python might raise an exception for <pre class='brush: python'>{1:2, 1:3} </pre> and that something I find very unlikely.

juestr on May 30, 2019, 1:30 p.m.
The Language Reference does explicitly specify the semantics of dict displays with duplicate keys, see <a href="https://docs.python.org/3/reference/expressions.html?highlight=dict%20literal">https://docs.python.org/3/reference/expressions.html?highlight=dict%20literal</a>#dictionary-displays. A true translation table can only be created for some strings (exactly those which pass the mission at hand), and there is no specification of the failure mode you rely on. Related, the spec mentions that both strings must be of the same length, again without a description of the failure mode. Experimentation shows it does raise a ValueError, indicating it does not just zip and create a dict, and not testing for a consistent table may be an oversight. <pre class='brush: python'>str.maketrans('abc', '12') --> ValueError: the first two maketrans arguments must have equal length </pre>

veky on May 30, 2019, 5:58 p.m.
I still think that the documentation maps almost exactly to Python implementation: <pre class='brush: python'>if len(args) == 2: # If there are two arguments, x, y = args # they assert isinstance(x, str) and isinstance(y, str) # must be strings assert len(x) == len(y) # of equal length, result = {} # and in the resulting dictionary, for cx, cy in zip(x, y): # each character in x result[cx] = cy # will be mapped to the character at the same position in y. </pre> And I don't see what's "inconsistent" there. But ok, I'm not too attached to categories anyway. :-)

juestr on May 30, 2019, 7:05 p.m.
Not a big deal, it's all fun and games here, undefined behavior can be a real bitch in large real world projects though. I guess we can agree to disagree on how narrow to interpret the documentation. The code is clear, but the doc doesn't even commit to return a dict. translate() doesn't require one either, but "translation table" could be read to imply a dict and common rules. 🤷‍♂️

veky on June 2, 2019, 5:45 p.m.
In Python (at least in Platonic Python:), there really is no such thing as undefined behavior. (There is a bit of implementation-defined behavior, but even that is very short-lived, since all the other implementations try really hard to mimic CPython as closely as possible.) To give you a bit of perspective, we're speaking about <a href="https://bugs.python.org/issue23624">this language</a>. Where consistent behavior in an undocumented case is still perceived as less important than backward compatibility. ;-O <hr /> <blockquote> but the doc doesn’t even commit to return a dict. </blockquote> To me, "in the resulting dictionary" seems like exactly that. :-| <blockquote> could be read to imply a dict and common rules. 🤷‍♂️ </blockquote> What I tried to tell you above is that "common rules" include the idea of later items overriding the former ones. And it has to be like that - for example, in vars(): x = 5 and then x = 8 must have x be 8 in the resulting namespace. :-)

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