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Arguments that do not stop the function from working even though there is nothing passed to it are known as optional arguments. Arguments whose presence is completely optional, their value will be taken by the program if provided. But if no value is given for a certain argument, the program will not halt.
You can assign an optional argument using the assignment operator in a function definition or using the Python **kwargs statement. There are two types of arguments a Python function can accept: positional and optional. Optional arguments are values that do not need to be specified for a function to be called.
Optional arguments enable you to omit arguments for some parameters. Both techniques can be used with methods, indexers, constructors, and delegates. When you use named and optional arguments, the arguments are evaluated in the order in which they appear in the argument list, not the parameter list.
Much like the manual, use an equals (=) sign in your definition of the parameters:
function dosomething($var1, $var2, $var3 = 'somevalue'){
// Rest of function here...
}
The default value of the argument must be a constant expression. It can't be a variable or a function call.
If you need this functionality however:
function foo($foo, $bar = false)
{
if(!$bar)
{
$bar = $foo;
}
}
Assuming $bar isn't expected to be a boolean of course.
Some notes that I also found useful:
Keep your default values on the right side.
function whatever($var1, $var2, $var3="constant", $var4="another")
The default value of the argument must be a constant expression. It can't be a variable or a function call.
Give the optional argument a default value.
function date ($format, $timestamp='') {
}
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