Exceptions and pre-conditions: Difference between revisions
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Be careful not to confuse an exception with an error. | Be careful not to confuse an exception with an error. | ||
An error "indicates serious problems that a reasonable application should not try to catch." An | An error "indicates serious problems that a reasonable application should not try to catch." An exception "indicates conditions that a reasonable application might want to catch."<ref>https://stackoverflow.com/questions/5813614/what-is-difference-between-errors-and-exceptions</ref>. | ||
We use the term "catch an exception" to catch exceptions and plan how the program should respond. | We use the term "catch an exception" to catch exceptions and plan how the program should respond. | ||
== Example == | == Example == | ||
<syntaxhighlight lang="python"> | <syntaxhighlight lang="python"> | ||
# here is some code with a deliberate error. There should be two apostrophe's for the end argument. | # here is some Python code with a deliberate error. There should be two apostrophe's for the end argument. | ||
print("hello world", end=') | print("hello world", end=') | ||
print("from Warsaw") | print("from Warsaw") | ||
print("=" * 25) | print("=" * 25) | ||
</syntaxhighlight> | </syntaxhighlight> | ||
When we execute this code we see the following exception: | |||
[[File:Exception example.png]] | [[File:Exception example.png|700px]] | ||
You can see there are four lines here: | |||
# on the first line we see the name of the file being executed and the '''line number''' where the exception was thrown. | |||
# on the second line we see the line of code where the exception was thrown | |||
# on the third line we see a carat (^) pointing the place where the exception was thrown | |||
# on the fourth line we see the description of the exception | |||
If you google the exception (line 4) you can often find helpful information about the exception. | |||
For a list of common exceptions, please [https://www.tutorialspoint.com/python/standard_exceptions.htm click here] | |||
== Standards == | == Standards == | ||
Latest revision as of 08:09, 27 September 2021
Exceptions[1]
An exception is an anomalous or exceptional condition requiring special processing – often changing the normal flow of program execution[2].
Be careful not to confuse an exception with an error.
An error "indicates serious problems that a reasonable application should not try to catch." An exception "indicates conditions that a reasonable application might want to catch."[3].
We use the term "catch an exception" to catch exceptions and plan how the program should respond.
Example[edit]
# here is some Python code with a deliberate error. There should be two apostrophe's for the end argument.
print("hello world", end=')
print("from Warsaw")
print("=" * 25)
When we execute this code we see the following exception:
You can see there are four lines here:
- on the first line we see the name of the file being executed and the line number where the exception was thrown.
- on the second line we see the line of code where the exception was thrown
- on the third line we see a carat (^) pointing the place where the exception was thrown
- on the fourth line we see the description of the exception
If you google the exception (line 4) you can often find helpful information about the exception. For a list of common exceptions, please click here
Standards[edit]
These standards are used from the IB Computer Science Subject Guide[4]
- Identify exceptions that need to be considered in a specified problem solution.
References[edit]
- ↑ http://www.flaticon.com/
- ↑ https://en.wikipedia.org/wiki/Exception_handling
- ↑ https://stackoverflow.com/questions/5813614/what-is-difference-between-errors-and-exceptions
- ↑ IB Diploma Programme Computer science guide (first examinations 2014). Cardiff, Wales, United Kingdom: International Baccalaureate Organization. January 2012.