boolean-expression

This question is based on another question I asked, where I didn't cover the problem entirely: Pandas - check if a string column contains a pair of strings This is a modified version of the question. I have two dataframes : df1 = pd.DataFrame({'consumption':['squirrel ate apple', 'monkey likes apple', 'monkey banana gets', 'badger gets banana', 'giraffe eats grass', 'badger apple loves', 'elephant is huge', 'elephant eats banana tree', 'squirrel digs in grass']}) df2 = pd.DataFrame({'food':['apple', 'apple', 'banana', 'banana'], 'creature':['squirrel', 'badger', 'monkey', 'elephant']}) The

I've been working with PHP for quite a while now, but this was always a mystery to me, the correct use of the exclamation mark (negative sign) in front of variables. What does !$var indicate? Is var false , empty, not set etc.? Here are some examples that I need to learn... Example 1: $string = 'hello'; $hello = (!empty($string)) ? $string : ''; if (!$hello) { die('Variable hello is empty'); } Is this example valid? Would the if statement really work if $string was empty? Example 2: $int = 5; $count = (!empty($int)) ? $int : 0; // Note the positive check here if ($count) { die('Variable count

This question already has an answer here: How do I pass variables and data from PHP to JavaScript? 19 answers I've run into an odd issue in a PHP script that I'm writing-- I'm sure there's an easy answer but I'm not seeing it. I'm pulling some vars from a DB using PHP, then passing those values into a Javascript that is getting built dynamically in PHP. Something like this: $myvar = (bool) $db_return->myvar; $js = "<script type=text/javascript> var myvar = " . $myvar . "; var myurl = 'http://someserver.com/ajaxpage.php?urlvar=myvar'; </script>"; The problem is that if the boolean value in the

Possible Duplicate: Is it bad to explicitly compare against boolean constants e.g. if (b == false) in Java? In this NotePadProvider sample code , I noticed that the author chose the form: if (values.containsKey(NoteColumns.CREATED_DATE) == false) { values.put(NoteColumns.CREATED_DATE, now); } Over: if (!values.containsKey(NoteColumns.CREATED_DATE)) { values.put(NoteColumns.CREATED_DATE, now); } Is there any advantage in the first form over the more logical one? Apart from "readability", no. They're functionally equivalent. ("Readability" is in quotes because I hate == false and find ! much

If you execute the following statement in Python 3.7, it will (from my testing) print b : if None.__eq__("a"): print("b") However, None.__eq__("a") evaluates to NotImplemented . Naturally, "a".__eq__("a") evaluates to True , and "b".__eq__("a") evaluates to False . I initially discovered this when testing the return value of a function, but didn't return anything in the second case -- so, the function returned None . What's going on here? This is a great example of why the __dunder__ methods should not be used directly as they are quite often not appropriate replacements for their equivalent

I would like to have the echo command executed when cat /etc/passwd | grep "sysa" is not true. What am I doing wrong? if ! [ $(cat /etc/passwd | grep "sysa") ]; then echo "ERROR - The user sysa could not be looked up" exit 2 fi shellter try if ! grep -q sysa /etc/passwd ; then grep returns true if it finds the search target, and false if it doesn't. So NOT false == true . if evaluation in shells are designed to be very flexible, and many times doesn't require chains of commands (as you have written). Also, looking at your code as is, your use of the $( ... ) form of cmd-substitution is to be

This question already has an answer here: Is <boolean expression> && statement() the same as if(<boolean expression>) statement()? 5 answers This should be quite a simple question I just couldn't find the answer anywhere so thought I'd save myself some time and ask here. I was looking at some javascript code and noticed an expression of the form: a < b && (other maths statements); The other maths statements are just assigning of variables and simple stuff. My question is this. Is this another way to write compact if statements? I know that statement?if-block:else-block; is one way to do it but

Is there a substantial difference in Python 3.x between: for each_line in data_file: if each_line.find(":") != -1: #placeholder for code #more placeholder and for each_line in data: if not each_line.find(":") == -1: #placeholder for code #more placeholder My question isn't particular to the above usage, but is more general or essential - is this syntactical difference working in a different way, even though the result is the same? Is there a logical difference? Are there tasks where one is more appropriate or is this solely a stylistic difference? If this is merely stylistic, which one is