not-operator

What's more efficient in Python: `key not in list` or `not key in list`? [duplicate]

由 ╄→尐↘猪︶ㄣ 提交于 2020-01-13 19:43:57
问题 This question already has answers here : “x not in y” or “not x in y” (6 answers) Closed 2 years ago . Just found out that both syntax ways are valid. Which is more efficient? element not in list Or: not element in list ? 回答1: They behave identically, to the point of producing identical byte code; they're equally efficient. That said, element not in list is usually considered preferred. PEP8 doesn't have a specific recommendation on not ... in vs. ... not in , but it does for not ... is vs. .

!flag has two meanings in java?

由 試著忘記壹切 提交于 2019-12-24 08:05:28
问题 boolean flag = false; if(!flag) System.out.println(!flag); // prints true I wonder why !flag being considered as false when it's a conditional parameter passed to if statement and as true elsewhere? 回答1: It's not. if (boolean expression) { statement } means "execute the statement if boolean expression is true." Since flag = false , !flag == true . Always. 回答2: !flag where flag is false evaluates to true in all contexts, including if statements. 回答3: !flag does not change the value of flag ,

mysql fulltext boolean NOT operator

由 一曲冷凌霜 提交于 2019-12-06 17:42:54
问题 I'm doing a MySQL FULLTEXT search in boolean mode. According to the manual : Note: The - operator acts only to exclude rows that are otherwise matched by other search terms. Thus, a boolean-mode search that contains only terms preceded by - returns an empty result. It does not return “all rows except those containing any of the excluded terms.” That's true. So I use the NOT MATCH operator like this : SELECT COUNT(*) FROM Table WHERE MATCH (Column) AGAINST ('bar' IN BOOLEAN MODE) AND NOT MATCH

Which is clearer form: if(!value) or if(flag == value)?

由 早过忘川 提交于 2019-11-29 21:14:10
I understand this is a subjective question, so I apologize if it needs to be closed, but I feel like it comes up often enough for me to wonder if there is a general preference for one form over the other. Obviously, the best answer is "refactor the code so you don't need to test for falsehood" but sometimes there's no easy way to do so and the "else" branch is simply to continue processing. So when you must have an "if not false" construct, which is the preferred standard: The not operator if (!value) Or the test for false if (value == false) KP. if (!value) is easier/faster to follow.

Which is clearer form: if(!value) or if(flag == value)?

由 我们两清 提交于 2019-11-28 17:19:19
问题 I understand this is a subjective question, so I apologize if it needs to be closed, but I feel like it comes up often enough for me to wonder if there is a general preference for one form over the other. Obviously, the best answer is "refactor the code so you don't need to test for falsehood" but sometimes there's no easy way to do so and the "else" branch is simply to continue processing. So when you must have an "if not false" construct, which is the preferred standard: The not operator if

What does “!--” do in JavaScript?

由 旧时模样 提交于 2019-11-28 14:56:44
I have this piece of code (taken from this question ): var walk = function(dir, done) { var results = []; fs.readdir(dir, function(err, list) { if (err) return done(err); var pending = list.length; if (!pending) return done(null, results); list.forEach(function(file) { file = path.resolve(dir, file); fs.stat(file, function(err, stat) { if (stat && stat.isDirectory()) { walk(file, function(err, res) { results = results.concat(res); if (!--pending) done(null, results); }); } else { results.push(file); if (!--pending) done(null, results); } }); }); }); }; I'm trying to follow it, and I think I

Should I use `!IsGood` or `IsGood == false`?

由 最后都变了- 提交于 2019-11-27 12:17:34
I keep seeing code that does checks like this if (IsGood == false) { DoSomething(); } or this if (IsGood == true) { DoSomething(); } I hate this syntax, and always use the following syntax. if (IsGood) { DoSomething(); } or if (!IsGood) { DoSomething(); } Is there any reason to use ' == true ' or ' == false '? Is it a readability thing? Do people just not understand Boolean variables? Also, is there any performance difference between the two? Patrick Desjardins I follow the same syntax as you, it's less verbose. People (more beginner) prefer to use == true just to be sure that it's what they

What does “!--” do in JavaScript?

由 会有一股神秘感。 提交于 2019-11-27 08:56:14
问题 I have this piece of code (taken from this question): var walk = function(dir, done) { var results = []; fs.readdir(dir, function(err, list) { if (err) return done(err); var pending = list.length; if (!pending) return done(null, results); list.forEach(function(file) { file = path.resolve(dir, file); fs.stat(file, function(err, stat) { if (stat && stat.isDirectory()) { walk(file, function(err, res) { results = results.concat(res); if (!--pending) done(null, results); }); } else { results.push

Python not equal operator

由 霸气de小男生 提交于 2019-11-27 05:34:50
I come from a c style languages, so I am natural in using != as not equal, but when I came to Python, from the documentation I read, I learned that for this purpose the <> operator is used. Recently, I have seen a lot of code using != , so my question is if one of them is preferred over the other or is one of them deprecated. Also, I would like to know if there is any difference between them. Python 2 supports both , in python 3 the <> operator has been removed. There is no difference between the two, but != is the preferred form . From the official docs you linked != can also be written <>,

Should I use `!IsGood` or `IsGood == false`?

由 牧云@^-^@ 提交于 2019-11-26 18:10:25
问题 I keep seeing code that does checks like this if (IsGood == false) { DoSomething(); } or this if (IsGood == true) { DoSomething(); } I hate this syntax, and always use the following syntax. if (IsGood) { DoSomething(); } or if (!IsGood) { DoSomething(); } Is there any reason to use ' == true ' or ' == false '? Is it a readability thing? Do people just not understand Boolean variables? Also, is there any performance difference between the two? 回答1: I follow the same syntax as you, it's less
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