Check if object exists in JavaScript
You can safely use the typeof operator on undefined variables. If it has been assigned any value, including null, typeof will return something other than undefined. typeof always returns a string. Therefore
variables
accessing a variable from another class
Very simple question but I can’t do it. I have 3 classes: DrawCircle class DrawFrame class CircMain class One class creates a frame, the other draws a circle and fills it with smaller circles. In DrawFrame I set width and height. In DrawCircle I need to access the width and height of DrawFrame. How do … Read more
Copy a list of list by value and not reference
Because python passes lists by reference This means that when you write “b=a” you’re saying that a and b are the same object, and that when you change b you change also a, and viceversa A way to copy a list by value: If the list contains objects and you want to copy them as … Read more
How to modify a global variable within a function in bash?
When you use a command substitution (i.e., the $(…) construct), you are creating a subshell. Subshells inherit variables from their parent shells, but this only works one way: A subshell cannot modify the environment of its parent shell. Your variable e is set within a subshell, but not the parent shell. There are two ways to pass values from … Read more
How to modify a global variable within a function in bash?
When you use a command substitution (i.e., the $(…) construct), you are creating a subshell. Subshells inherit variables from their parent shells, but this only works one way: A subshell cannot modify the environment of its parent shell. Your variable e is set within a subshell, but not the parent shell. There are two ways to pass values from … Read more
Printing variables in Python 3.4
The syntax has changed in that print is now a function. This means that the % formatting needs to be done inside the parenthesis:1 However, since you are using Python 3.x., you should actually be using the newer str.format method: Though % formatting is not officially deprecated (yet), it is discouraged in favor of str.format and will most likely be removed from the language in a coming … Read more
Viewing all defined variables
A few things you could use: dir() will give you the list of in scope variables: globals() will give you a dictionary of global variables locals() will give you a dictionary of local variables
What is the PHP syntax to check “is not null” or an empty string?
Null OR an empty string? Use empty(). After realizing that $user ~= $_POST[‘user’] (thanks matt):
Create timestamp variable in bash script
In order to get the current timestamp and not the time of when a fixed variable is defined, the trick is to use a function and not a variable: If you don’t like the format given by the %T specifier you can combine the other time conversion specifiers accepted by date. For GNU date, you can find the complete list of … Read more
Variable might not have been initialized error
You declared them, but you didn’t initialize them. Initializing them is setting them equal to a value: You get the error because you haven’t initialized the variables, but you increment them (e.g., a++) in the for loop. Java primitives have default values but as one user commented below Their default value is zero when declared … Read more