Exception handling

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The bucket brigade approach to putting out a fire is to pass buckets of water along a chain of people.

Many programmers use the bucket brigade approach to error handling.

Note: This is easier for programs that can return multiple results, or those that more easily support reference parameters.

Note: The variable ec for "error code" is used where a zero indicates no error and non-zero provides the error code of what happened. Here is the Python code.

def div4(x1, y1):
	print("x=[{0:3.1f}] y=[{1:3.1f}]".format(x1,y1))
	z1 = 0
	ec = 1
	if y1 != 0:
		ec = 1
		z1 = x1 / y1
		print("z=[{0:3.1f}]".format(z1))
	return ec,z1


def div3(x1, y1):
	ec,z1 = div4(x1,y1)
	return ec,z1


def div2(x1, y1):
	ec,z1 = div3(x1,y1)
	return ec,z1


def div1(x1, y1):
	ec,z1 = div2(x1,y1)
	return ec,z1

x1 = 6.0
y1 = 0.0
ec,z1 = div1(x1,y1)
if ec == 0:
	print("ok")
else:
	print("error")

Here is the output of the Python code.

x=[6.0] y=[0.0]
error

The bucket brigade is a MTTF (Mean Time To Failure) approach that attempts to find and handle any error that might be encountered.

Here is the Python code.

def div1(x1, y1):
	print("x=[{0:3.1f}] y=[{1:3.1f}]".format(x1,y1))
	z1 = x1 / y1
	print("z=[{0:3.1f}]".format(z1))
	return z1

x1 = 6.0
y1 = 2.0
z1 = div1(x1,y1)
y1 = 0.0
try:
	z1 = div1(x1,y1)
except:
	print("except")
finally:
	print("finally")
print("done")

Here is the output of the Python code.

x=[6.0] y=[2.0]
z=[3.0]
x=[6.0] y=[0.0]
except
finally
done

Note that Python has various types of exceptions that can be used.

Is is also possible to raise an exception via code.

Here is the JavaScript code.

function div1(x1, y1) {
	console.log("x=["+x1+"] y=["+y1+"]\n");
	var z1 = x1 / y1;
	console.log("z=["+z1+"]\n");
	return z1;
	}
var x1 = 6.0;
var y1 = 2.0;
var z1 = div1(x1,y1);
y1 = 0.0;
try {
	z1 = div1(x1,y1);
	}
catch (e1) {
	console.log("except\n");
	}
finally {
	console.log("finally\n");
	}
console.log("done\n");

Here is the output of the JavaScript code.

x=[6] y=[2]

z=[3]

x=[6] y=[0]

z=[Infinity]

finally

done

Notice that JavaScript does not actually catch the exception. It keeps on going.

In JavaScript, a division by zero is defined. It is Infinity for "infinity"!

Here is the PHP code.

<?php

function div1($x1, $y1) {
	printf("x=[%3.1f] y=[%3.1f]\n",$x1,$y1);
	$z1 = $x1 / $y1;
	printf("z=[%3.1f]\n",$z1);
	return $z1;
	}
$x1 = 6.0;
$y1 = 2.0;
$z1 = div1($x1,$y1);
$y1 = 0.0;
try {
	$z1 = div1($x1,$y1);
	}
catch (Exception $e) {
	printf("except\n");
	}
finally {
	printf("finally\n");
	}
printf("done\n");
?>

Here is the output of the PHP code.

x=[6.0] y=[2.0]
z=[3.0]
x=[6.0] y=[0.0]

Warning: Division by zero in D:\W\PROGRAM1.PHP\try11a-01.php on line 5
z=[INF]
finally
done

Notice that PHP does not actually catch the exception. It keeps on going.

In PHP, a division by zero is defined. It is INF for "infinity"!