Ruby Exception Handling: ZeroDivisionError

Today in our continued journey through our Ruby Exception Handling series we'll be taking a closer look at the ZeroDivionError. As you may suspect the ZeroDivisionError occurs when attempting to divide a number by zero.

In this article we'll briefly explore the ZeroDivisionError in more detail, including where it sits within the Ruby Exception class hierarchy and showing a few simple code examples to illustrate how ZeroDivisionErrors occur in the first place. Let's get started!

The Technical Rundown

• All Ruby exceptions are descendants of the Exception class, or a subclass therein.
• StandardError is a direct descendant of the Exception class, and is also a superclass with many descendants of its own.
• ZeroDivisionError is the direct descendant of StandardError.

When Should You Use It?

Producing a ZeroDivisionError is quite simple, but there are a few small quirks that you'll want to be aware of before assuming your rescue ZeroDivisionError => e statement will always catch attempts to divide by zero-ish values. To illustrate we have a few example methods showing normal division, division by exactly zero, division by floating zero, and division by negative floating zero. As usual we'll start with the full code snippet and then we'll briefly go through it to see what's going on:

def execute_examples

    division_example

    Logging.line_separator

    zero_division_example

    Logging.line_separator

    floating_zero_division_example

    Logging.line_separator

    negative_floating_zero_division_example

end
def division_example
 begin
 # Set the numerator.
 numerator = 15
 # Set the denominator.
 denominator = 5
 # Divide and output the result.
 Logging.log(numerator / denominator)
 #=> 3
 rescue ZeroDivisionError => e
 Logging.log(e)
 rescue => e
 Logging.log(e, { explicit: false })
 end
 end
def zero_division_example
 begin
 # Set the numerator.
 numerator = 15
 # Set the denominator to zero.
 denominator = 0
 # Try to divide and output the result.
 Logging.log(numerator / denominator)
 #=> (EXPLICIT) ZeroDivisionError: divided by 0
 rescue ZeroDivisionError => e
 Logging.log(e)
 rescue => e
 Logging.log(e, { explicit: false })
 end
 end
def floating_zero_division_example
 begin
 # Set the numerator.
 numerator = 15
 # Set the denominator to zero as float.
 denominator = 0.0
 # Try to divide and output the result.
 Logging.log(numerator / denominator)
 #=> Infinity
 rescue ZeroDivisionError => e
 Logging.log(e)
 rescue => e
 Logging.log(e, { explicit: false })
 end
 end
def negative_floating_zero_division_example
 begin
 # Set the numerator.
 numerator = 15
 # Set the denominator to negative zero as float.
 denominator = -0.0
 # Try to divide and output the result.
 Logging.log(numerator / denominator)
 #=> -Infinity
 rescue ZeroDivisionError => e
 Logging.log(e)
 rescue => e
 Logging.log(e, { explicit: false })
 end
 end
# Execute examples.
 execute_examples
module Logging
 extend Utility
 class << self
 # Outputs +value+ to console.
 # +args+ may include:
 # +:explicit+ (Boolean) - Is +Exception+ class +value+ expected? [default: true]
 # +:timestamp+ (Boolean) - Should timestamp be included? [default: false]
 #
 # Examples:
 #
 # Logging.log('My message') #=> "My message"
 # Logging.log('My message', { timestamp: true} ) #=> "[12:00:05] My message"
 #
 # begin
 # raise Exception.new('An exception!')
 # rescue Exception => e
 # Logging.log(e)
 # end
 # #=> (EXPLICIT) Exception: An exception!
 # #=> (...backtrace...)
 def log(value, args = {})
 # Check if exception was explicit.
 explicit = args[:explicit].nil? ? true : args[:explicit]
 # Get timestamp if necessary.
 timestamp = args[:timestamp] ? formatted_timestamp : ""
 if value.is_a?(Exception)
 # If +value+ is an +Exception+ type output formatted exception.
 puts timestamp << formatted_exception(value, explicit)
 elsif value.is_a?(String)
 # If +value+ is a +String+ directly output
 puts timestamp << value
 else
 # If +value+ is anything else output.
 puts timestamp if !timestamp.empty?
 puts value
 end
 end
 # Output the specified +separator+ +count+ times to log.
 # +args may include:
 # +:count+ (Integer) - Number of characters to output. [default: 20]
 # +:separator+ (String) - Character or string to duplicate and output. [default: '-']
 def line_separator(args = {})
 count = args[:count].nil? ? 20 : args[:count]
 separator = args[:separator].nil? ? '-' : args[:separator]
 # Concatenate and output.
 puts separator * count
 end
 private
 def formatted_exception(exception, explicit)
 # Set explicit or inexplicit tag.
 output = "(#{explicit ? 'EXPLICIT' : 'INEXPLICIT'}) "
 # Add class and message.
 output << "#{exception.class}: #{exception.message}\n"
 # Append backtrace with leading tabs.
 output << "\t" << exception.backtrace.join("\n\t")
 # Return output string.
 output
 end
 def formatted_timestamp
 "[#{Time.now.strftime("%T")}] "
 end
 end
 end
 

We start with a normal and functional #division_example method:

def division_example

    begin

        # Set the numerator.

        numerator = 15

        # Set the denominator.

        denominator = 5

        # Divide and output the result.

        Logging.log(numerator / denominator)

        #=> 3

    rescue ZeroDivisionError => e

        Logging.log(e)

    rescue => e

        Logging.log(e, { explicit: false })

    end

end

This works as expected and outputs a result of 3. However, if we change our denominator to 0 we'll produce a ZeroDivisionError, as seen in #zero_division_example:

def zero_division_example

    begin

        # Set the numerator.

        numerator = 15

        # Set the denominator to zero.

        denominator = 0

        # Try to divide and output the result.

        Logging.log(numerator / denominator)

        #=> (EXPLICIT) ZeroDivisionError: divided by 0

    rescue ZeroDivisionError => e

        Logging.log(e)

    rescue => e

        Logging.log(e, { explicit: false })

    end

end

That should make sense to most of us I think: Just like when you were bored in school and were messing around with your calculator and tried dividing by zero you'd get an error, the same applies in Ruby (and probably all other programming languages for that matter). However, dividing by zero in all cases may not work exactly as you'd think. Watch what happens when we change our denominator from 0 to a floating point representation of 0.0:

def floating_zero_division_example

    begin

        # Set the numerator.

        numerator = 15

        # Set the denominator to zero as float.

        denominator = 0.0

        # Try to divide and output the result.

        Logging.log(numerator / denominator)

        #=> Infinity

    rescue ZeroDivisionError => e

        Logging.log(e)

    rescue => e

        Logging.log(e, { explicit: false })

    end

end

Suddenly we no longer produce a ZeroDivisionError but, instead, we get an output of Infinity. This is because Ruby handles various numeric data object types differently: whole numbers or Integers like 0 are calculated differently than Floats like 0.0.

We can see this strangeness continue if we change the denominator from 0.0 to the negative version of -0.0, which produces an output of negative Infinity:

def negative_floating_zero_division_example

    begin

        # Set the numerator.

        numerator = 15

        # Set the denominator to negative zero as float.

        denominator = -0.0

        # Try to divide and output the result.

        Logging.log(numerator / denominator)

        #=> -Infinity

    rescue ZeroDivisionError => e

        Logging.log(e)

    rescue => e

        Logging.log(e, { explicit: false })

    end

end

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