negate

问题 How would I use a negative form of Python's isinstance()? Normally negation would work something like x != 1 if x not in y if not a I just haven't seen an example with isinstance(), so I'd like to know if there's a correct way to used negation with isinstance(). 回答1: Just use not . isinstance just returns a bool , which you can not like any other. 回答2: That would seem strange, but: if not isinstance(...): ... The isinstance function returns a boolean value. That means that you can negate it

问题 How would I use a negative form of Python's isinstance()? Normally negation would work something like x != 1 if x not in y if not a I just haven't seen an example with isinstance(), so I'd like to know if there's a correct way to used negation with isinstance(). 回答1: Just use not . isinstance just returns a bool , which you can not like any other. 回答2: That would seem strange, but: if not isinstance(...): ... The isinstance function returns a boolean value. That means that you can negate it

来源： https://stackoverflow.com/questions/3412190/net-decimal-negate-vs-multiplying-by-1

来源： https://stackoverflow.com/questions/3412190/net-decimal-negate-vs-multiplying-by-1

问题 Im writing a simple folder watcher program, I would like to ignore a temp.temp file that gets copied into the folder when a scan is made, so the program will detect anything placed in the folder and ignore the temp.temp file. At the moment I have got the program detecting IMG files to get around the problem. if(e.FullPath.Contains("IMG")) { MessageBox.Show("You have a Collection Form: " + e.Name); Process.Start("explorer.exe", e.FullPath); } 回答1: Try : If(!e.FullPath.EndsWith("temp.temp"))

问题 if a string has this predicted format: value = "hello and good morning" Where the " (quotations) might also be ' (single quote), and the closing char (' or ") will be the same as the opening one. I want to match the string between the quotation marks. \bvalue\s*=\s*(["'])([^\1]*)\1 (the two \s are to allow any spaces near the = sign) The first "captured group" (inside the first pair of brackets) - should match the opening quotation which should be either ' or " then - I'm supposed to allow

问题 In Ruby, the operation of point - 20 # treating it as point - (20,20) 20 - point # treating it as (20,20) - point are to be implemented. But the following code: class Point attr_accessor :x, :y def initialize(x,y) @x, @y = x, y end def -(q) if (q.is_a? Fixnum) return Point.new(@x - q, @y - q) end Point.new(@x - q.x, @y - q.y) end def -@ Point.new(-@x, -@y) end def *(c) Point.new(@x * c, @y * c) end def coerce(something) [self, something] end end p = Point.new(100,100) q = Point.new(80,80) p (

问题 This question already has answers here : Closed 7 years ago . Possible Duplicate: What does the exclamation mark do before the function? I was looking through the Twitter Bootstrap JavaScript code and I noticed all their plugins are wrapped in negating self invoking functions. I am aware that function ($) { ... }(window.jQuery); invokes the function immediately. But what is the ! for? 回答1: 1) if you just do: function () { /* ... */ }(); You will get an error. JS will not allow you to fire off

问题 When dealing with generic code in C++, I would find a std::identity functor (like std::negate ) very useful. Is there a particular reason why this is not present in the standard library? 回答1: Soon after std::identity was introduced, issues began to appear, starting with conflicts to pre-cpp98 definitions of std::identity appearing as extensions: https://groups.google.com/a/isocpp.org/forum/#!topic/std-proposals/vrrtKvA7cqo This site might give a little more history for it. 来源： https:/

问题 How can I write the following rule in PROLOG: if P then not Q I understand that you can easily write if P then Q the predicates like q(X) :- p(X) , but how can you negate the q/1 predicate? I don't want to define new predicates with other semantics like non_q/1 . 回答1: The clause "if P then not Q" is logically equivalent to the negative clause "not P OR not Q". As such it is a Horn clause without a positive literal, and as an application of the correspondence of SLD theorem proving and Horn