Any falsy value will satisfy the if(!insert_variable_here) condition, including: false null undefined The empty string ” The number 0 NaN If callback return evaluates any of those values, the condition will be satisfied. Even though null != false, the following will give you an alert: x = null; if(!x) { alert(‘”!null” does evaluate to true’); … Read more
You shouldn’t worry about performance unless your code is in a tight inner loop, and is actually a performance problem. Instead, use code that best expresses your intent. Some people like lambdas, some like itemgetter. Sometimes it’s just a matter of taste. itemgetter is more powerful, for example, if you need to get a number … Read more
When Python attempts to multiply two objects, it first tries to call the left object’s __mul__() method. If the left object doesn’t have a __mul__() method (or the method returns NotImplemented, indicating it doesn’t work with the right operand in question), then Python wants to know if the right object can do the multiplication. If … Read more
There are three options: >>> 4 / float(100) 0.04 >>> 4 / 100.0 0.04 which is the same behavior as the C, C++, Java etc, or >>> from __future__ import division >>> 4 / 100 0.04 You can also activate this behavior by passing the argument -Qnew to the Python interpreter: $ python -Qnew >>> … Read more
There is no ordering between the increment and the dereference. However, the * operator applies to the result of p++, which is the original value of p prior to the increment.
These are called Pre and Post Increment / Decrement Operators. x++; is the same as x = x + 1; x–; is the same as x = x – 1; Putting the operator before the variable ++x; means, first increment x by 1, and then use this new value of x int x = 0; … Read more
Take a look at What every computer scientist should know about floating point numbers. Squeezing infinitely many real numbers into a finite number of bits requires an approximate representation…. — Edit to show what the above quote means — You shouldn’t ever compare floats or doubles for equality; because, you can’t really guarantee that the … Read more
It returns a single character string. It is the shortest way to write a single-character string literal. Use it when you want to define a lot of single-character strings. It is a heritage from Ruby <1.9, where it used to return the ASCII code for that character. I don’t understand what you mean by “break … Read more
This is, in effect, a way to check whether the expression e can be evaluated to be 0, and if not, to fail the build. The macro is somewhat misnamed; it should be something more like BUILD_BUG_OR_ZERO, rather than …ON_ZERO. (There have been occasional discussions about whether this is a confusing name.) You should read … Read more