4 ms·

Elliptical Python Programming

184 points by sebg 2y ago

benob 2y ago
TIL that in python, 1--2==3
- seplox 2y ago
  It's not a python thing. 1-(-2), distribute the negative.
  - qsort 2y ago
    In most C-like languages that would be a syntax error. E.g. in C and C++ as a rule you tokenize "greedily", "1--2" would be tokenized as "1", "unary decrement operator", "2", which is illegal because you're trying to decerment an rvalue. Python doesn't have "--", which allows the tokenizer to do something else.
    - nyrikki 2y ago
      In C, that is really because Unary minus (negation) has precedence over binary operations. +a - b; // equivalent to (+a) - b, NOT +(a - b) -c + d; // equivalent to (-c) + d, NOT -(c + d) https://en.cppreference.com/w/cpp/language/operator_arithmetic https://en.cppreference.com/w/cpp/language/operator_arithmet... +-e; // equivalent to +(-e), the unary + is a no-op if “e” is a built-in type // because any possible promotion is performed during negation already The same doesn't apply to, !! Which is applied as iterated binary operations (IIRC) I am pretty sure the decriment operator came around well after that quirk was established.
      - seanhunter 2y ago
        Peter van der Linden’s book “Expert C Programming” (which is awesome btw) says that one of them (Kernighan, Richie or maybe Ken Thompson I forget) realised early on that the c compiler had the wrong operator precedence for bit twiddling and unary and boolean operators but “at that stage we had a few thousand lines of C code and thought it would be too disruptive to change it”
    - j2kun 2y ago
      Also worth noting that `1 - -2` works and produces 3 in C because the space breaks the operator.
plus 2y ago
For those who are curious, `...` is a placeholder value in Python called Ellipsis. I don't believe it serves any real purpose other than being a placeholder. But it is an object and it implements `__eq__`, and is considered equal to itself. So `...==...` evaluates to `True`. When you prefix a `True` with `-`, it is interpreted as a prefix negation operator and implicitly converts the `True` to a `1`, so `-(...==...)` is equal to `-1`. Then, you add another prefix `-` to turn the `-1` back into `1`. `--(...==...)--(...==...)` evaluates to `2` because the first block evaluates to 1, as previously mentioned, and then the next `-` is interpreted as an infix subtraction operator. The second `-(...==...)` evaluates to `-1`, so you get `1 - -1` or `2`. When chaining multiple together, you can leave off the initial `--`, because booleans will be implicitly converted to integers if inserted into an arithmetic expression, e.g. `True - -1` -> `1 - -1` -> `2`. > There should be one-- and preferably only one --obvious way to do it. This article is obviously completely tongue-in-cheek, but I feel the need to point out that this sentence is not meant to be a complete inversion of the Perl philosophy of TIMTOWTDI. The word "obvious" is crucial here - there can be more than one way, but ideally only one of the ways is obvious.
- pletnes 2y ago
  Numpy actively uses … to make slicing multidimensional arrays less verbose. There are also uses in FastAPI along the lines of «go with the default».
- abuckenheimer 2y ago
  excellent explanation, to add to this since I was curious about the composition, '%c' is an integer presentation type that tells python to format numbers as their corresponding unicode characters[1] so '%c' * (length_of_string_to_format) % (number, number, ..., length_of_string_to_format_numbers_later) is the expression being evaluated here after you collapse all of the 1s + math formatting each number in the tuple as a unicode char for each '%c' escape in the string corresponding to its place in the tuple. [1] https://docs.python.org/3/library/string.html#format-specification-mini-language https://docs.python.org/3/library/string.html#format-specifi...
- nomel 2y ago
  Expanding on this a little, I will be replacing all occurrences of 2 with two blobs fighting, with shields: >>> 0^((...==...)--++--(...==...))^0 2
elijahbenizzy 2y ago
Ok do this but for JavaScript
- voidUpdate 2y ago
  https://en.wikipedia.org/wiki/JSFuck https://en.wikipedia.org/wiki/JSFuck
mariocesar 2y ago
If you're curious, the code in ellipsis results in executing: print('hello, world')
- mturmon 2y ago
  Thank you! I noticed some ** and * in the thing sent to eval(), which (given that the building blocks are small integers) seemed related to prime factorizations. The initial %c is duplicated 21 times (3*7, if I read correctly), and then string-interpolated (%c%c%c...) against a long tuple of integers. These integers themselves are composed of products of factors combined using * and **. There is also one tuple "multiplication" embedded within that long tuple of integers -- (a,b)*2 = (a,b,a,b). That is for the 'l' 'l' in "hello". It's all very clever and amusingly mathy, with a winking allusion to the construction of natural numbers using sets. It made me Godel.
callamdelaney 2y ago
I think we're really starting to over crowd pythons syntax and I'm not a fan.
- noddleah 2y ago
  you're telling me you never program in python elliptically??
- acbart 2y ago
  Pretty sure this would have been possible in Python 2.6. The Ellipsis object has been around for a very long time.
MadVikingGod 2y ago
This behavior can be replicated with any class that has two special methods: __neg__ that returns -1 and __sub__ that accepts ints and returns 1-other. For example if you make this class: class _: def __neg__(self): return -1 def __sub__(self, other): return 1-other You get similar behavior: >>> --_() 1 >>> _()--_() 2 Fun python for everyone.
maxloh 2y ago
You can do this on JavaScript too. alert(1) // equals to: [][(![]+[])[+!+[]]+(!![]+[])[+[]]][([][(![]+[])[+!+[]]+(!![]+[])[+[]]]+[])[!+[]+!+[]+!+[]]+(!![]+[][(![]+[])[+!+[]]+(!![]+[])[+[]]])[+!+[]+[+[]]]+([][[]]+[])[+!+[]]+(![]+[])[!+[]+!+[]+!+[]]+(!![]+[])[+[]]+(!![]+[])[+!+[]]+([][[]]+[])[+[]]+([][(![]+[])[+!+[]]+(!![]+[])[+[]]]+[])[!+[]+!+[]+!+[]]+(!![]+[])[+[]]+(!![]+[][(![]+[])[+!+[]]+(!![]+[])[+[]]])[+!+[]+[+[]]]+(!![]+[])[+!+[]]]((![]+[])[+!+[]]+(![]+[])[!+[]+!+[]]+(!![]+[])[!+[]+!+[]+!+[]]+(!![]+[])[+!+[]]+(!![]+[])[+[]]+([][(![]+[])[+!+[]]+(!![]+[])[+[]]]+[])[+!+[]+[+!+[]]]+[+!+[]]+([]+[]+[][(![]+[])[+!+[]]+(!![]+[])[+[]]])[+!+[]+[!+[]+!+[]]])() https://jsfuck.com/ https://jsfuck.com/
- deleted 2y ago
  [deleted]
curtisszmania 2y ago
[dead]
budmichstelk 2y ago
[dead]

184 points by sebg 2y ago

benob 2y ago

TIL that in python, 1--2==3

seplox 2y ago
It's not a python thing. 1-(-2), distribute the negative.
- qsort 2y ago
  In most C-like languages that would be a syntax error. E.g. in C and C++ as a rule you tokenize "greedily", "1--2" would be tokenized as "1", "unary decrement operator", "2", which is illegal because you're trying to decerment an rvalue. Python doesn't have "--", which allows the tokenizer to do something else.
  - nyrikki 2y ago
    In C, that is really because Unary minus (negation) has precedence over binary operations. +a - b; // equivalent to (+a) - b, NOT +(a - b) -c + d; // equivalent to (-c) + d, NOT -(c + d) https://en.cppreference.com/w/cpp/language/operator_arithmetic https://en.cppreference.com/w/cpp/language/operator_arithmet... +-e; // equivalent to +(-e), the unary + is a no-op if “e” is a built-in type // because any possible promotion is performed during negation already The same doesn't apply to, !! Which is applied as iterated binary operations (IIRC) I am pretty sure the decriment operator came around well after that quirk was established.
    - seanhunter 2y ago
      Peter van der Linden’s book “Expert C Programming” (which is awesome btw) says that one of them (Kernighan, Richie or maybe Ken Thompson I forget) realised early on that the c compiler had the wrong operator precedence for bit twiddling and unary and boolean operators but “at that stage we had a few thousand lines of C code and thought it would be too disruptive to change it”
  - j2kun 2y ago
    Also worth noting that `1 - -2` works and produces 3 in C because the space breaks the operator.

plus 2y ago

For those who are curious, `...` is a placeholder value in Python called Ellipsis. I don't believe it serves any real purpose other than being a placeholder. But it is an object and it implements `__eq__`, and is considered equal to itself. So `...==...` evaluates to `True`. When you prefix a `True` with `-`, it is interpreted as a prefix negation operator and implicitly converts the `True` to a `1`, so `-(...==...)` is equal to `-1`. Then, you add another prefix `-` to turn the `-1` back into `1`. `--(...==...)--(...==...)` evaluates to `2` because the first block evaluates to 1, as previously mentioned, and then the next `-` is interpreted as an infix subtraction operator. The second `-(...==...)` evaluates to `-1`, so you get `1 - -1` or `2`. When chaining multiple together, you can leave off the initial `--`, because booleans will be implicitly converted to integers if inserted into an arithmetic expression, e.g. `True - -1` -> `1 - -1` -> `2`. > There should be one-- and preferably only one --obvious way to do it. This article is obviously completely tongue-in-cheek, but I feel the need to point out that this sentence is not meant to be a complete inversion of the Perl philosophy of TIMTOWTDI. The word "obvious" is crucial here - there can be more than one way, but ideally only one of the ways is obvious.

pletnes 2y ago
Numpy actively uses … to make slicing multidimensional arrays less verbose. There are also uses in FastAPI along the lines of «go with the default».
abuckenheimer 2y ago
excellent explanation, to add to this since I was curious about the composition, '%c' is an integer presentation type that tells python to format numbers as their corresponding unicode characters[1] so '%c' * (length_of_string_to_format) % (number, number, ..., length_of_string_to_format_numbers_later) is the expression being evaluated here after you collapse all of the 1s + math formatting each number in the tuple as a unicode char for each '%c' escape in the string corresponding to its place in the tuple. [1] https://docs.python.org/3/library/string.html#format-specification-mini-language https://docs.python.org/3/library/string.html#format-specifi...
nomel 2y ago
Expanding on this a little, I will be replacing all occurrences of 2 with two blobs fighting, with shields: >>> 0^((...==...)--++--(...==...))^0 2

elijahbenizzy 2y ago

Ok do this but for JavaScript

voidUpdate 2y ago
https://en.wikipedia.org/wiki/JSFuck https://en.wikipedia.org/wiki/JSFuck

mariocesar 2y ago

If you're curious, the code in ellipsis results in executing: print('hello, world')

mturmon 2y ago
Thank you! I noticed some ** and * in the thing sent to eval(), which (given that the building blocks are small integers) seemed related to prime factorizations. The initial %c is duplicated 21 times (3*7, if I read correctly), and then string-interpolated (%c%c%c...) against a long tuple of integers. These integers themselves are composed of products of factors combined using * and **. There is also one tuple "multiplication" embedded within that long tuple of integers -- (a,b)*2 = (a,b,a,b). That is for the 'l' 'l' in "hello". It's all very clever and amusingly mathy, with a winking allusion to the construction of natural numbers using sets. It made me Godel.

callamdelaney 2y ago

I think we're really starting to over crowd pythons syntax and I'm not a fan.

noddleah 2y ago
you're telling me you never program in python elliptically??
acbart 2y ago
Pretty sure this would have been possible in Python 2.6. The Ellipsis object has been around for a very long time.

MadVikingGod 2y ago

This behavior can be replicated with any class that has two special methods: __neg__ that returns -1 and __sub__ that accepts ints and returns 1-other. For example if you make this class: class _: def __neg__(self): return -1 def __sub__(self, other): return 1-other You get similar behavior: >>> --_() 1 >>> _()--_() 2 Fun python for everyone.

maxloh 2y ago

You can do this on JavaScript too. alert(1) // equals to: [][(![]+[])[+!+[]]+(!![]+[])[+[]]][([][(![]+[])[+!+[]]+(!![]+[])[+[]]]+[])[!+[]+!+[]+!+[]]+(!![]+[][(![]+[])[+!+[]]+(!![]+[])[+[]]])[+!+[]+[+[]]]+([][[]]+[])[+!+[]]+(![]+[])[!+[]+!+[]+!+[]]+(!![]+[])[+[]]+(!![]+[])[+!+[]]+([][[]]+[])[+[]]+([][(![]+[])[+!+[]]+(!![]+[])[+[]]]+[])[!+[]+!+[]+!+[]]+(!![]+[])[+[]]+(!![]+[][(![]+[])[+!+[]]+(!![]+[])[+[]]])[+!+[]+[+[]]]+(!![]+[])[+!+[]]]((![]+[])[+!+[]]+(![]+[])[!+[]+!+[]]+(!![]+[])[!+[]+!+[]+!+[]]+(!![]+[])[+!+[]]+(!![]+[])[+[]]+([][(![]+[])[+!+[]]+(!![]+[])[+[]]]+[])[+!+[]+[+!+[]]]+[+!+[]]+([]+[]+[][(![]+[])[+!+[]]+(!![]+[])[+[]]])[+!+[]+[!+[]+!+[]]])() https://jsfuck.com/ https://jsfuck.com/

deleted 2y ago
[deleted]

curtisszmania 2y ago

[dead]

budmichstelk 2y ago

[dead]