7 ms·

It's not a python thing. 1-(-2), distribute the negative.

• qsort 1y 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 1y 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 1y 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 1y ago
    Also worth noting that `1 - -2` works and produces 3 in C because the space breaks the operator.