What is the difference between a mutable and immutable string in C# and VB.NET?
A mutable string can be changed.
An immutable string cannot be changed.
Mutable is the english word for can change. Immutable is the english word for cannot change.
if you alter a String, you are creating a new string object internally. So String is immutable. If you alter a StringBuilder no new Objects are created internally so, StringBuilder is mutable.
To show or hide a variable if null in AngularJs, you can use the snippet below.
<div ng-show="myVariable == null"></div>
<div ng-show="myvar != null"></div>
To check if a variable exists in Python, you can use the snippet below.
if 'myVariable' in locals(): # myVariable exists locally.
if 'myVariable' in globals(): # myVariable exists globally.