Python:Control structures - Revision history

Hdridder at 09:55, 29 July 2026

2026-07-29T09:55:03Z

← Older revision		Revision as of 09:55, 29 July 2026
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	A full list of exception-classes can be found in the [https://docs.python.org/3/library/exceptions.html#exception-hierarchy python docs]		A full list of exception-classes can be found in the [https://docs.python.org/3/library/exceptions.html#exception-hierarchy python docs]

	;raise(<~~Exception~~>)		;raise <Exception>(<text>)
	:Raise an <Exception> exception, <Exception>-class must exist		:Raise an <Exception> exception, <Exception>-class must exist, <text> is up to you.

	===Traceback===		===Traceback===

Hdridder: /* Exception handling */

2025-10-22T12:03:45Z

Exception handling

← Older revision		Revision as of 12:03, 22 October 2025
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	==Exception handling==		==Exception handling==

			Exceptions are used a lot by python programmers. The mantra is: "Easier to ask for forgiveness than permission" aka EAFP; and it is said to be faster.

	To catch exceptions:		To catch exceptions:
	<syntaxhighlight lang=python>		<syntaxhighlight lang=python>
Line 48:		Line 51:
	NOTE: elif is not allowed here.		NOTE: elif is not allowed here.

	Specifying a specific exception is optional but highly recommended ~~(Easier to ask for forgiveness than permission aka EAFP) and it is said to be faster~~. However, take care you don't forgive real faults.		Specifying a specific exception is optional but highly recommended. However, take care you don't forgive real faults.

	If more exceptions are defined with 1 try only 1 exception block will be executed,		If more exceptions are defined with 1 try only 1 exception block will be executed,
Line 72:		Line 75:
	:The index does not exist in the list		:The index does not exist in the list

	A full list of exception-~~types~~ can be found in the [https://docs.python.org/3/library/exceptions.html#exception-hierarchy python docs]		A full list of exception-classes can be found in the [https://docs.python.org/3/library/exceptions.html#exception-hierarchy python docs]

			;raise(<Exception>)
			:Raise an <Exception> exception, <Exception>-class must exist

	===Traceback===		===Traceback===

Hdridder: /* Exception handling */

2025-07-30T07:03:08Z

Exception handling

← Older revision		Revision as of 07:03, 30 July 2025
Line 52:		Line 52:
	If more exceptions are defined with 1 try only 1 exception block will be executed,		If more exceptions are defined with 1 try only 1 exception block will be executed,

	For reporting where the exception happened use [[~~Python~~#~~traceback\|~~traceback]]		For reporting where the exception happened use [[#traceback]].

	;except <exception> as ex		;except <exception> as ex
Line 73:		Line 73:

	A full list of exception-types can be found in the [https://docs.python.org/3/library/exceptions.html#exception-hierarchy python docs]		A full list of exception-types can be found in the [https://docs.python.org/3/library/exceptions.html#exception-hierarchy python docs]

			===Traceback===
			Show where things went wrong
			<syntaxhighlight lang=python>
			import traceback
			tracetext = traceback.format_exc() # Return info as string
			traceback.print_exc() # Print the info
			</syntaxhighlight>

	==Warnings==		==Warnings==

Hdridder: /* userWarnings */

2025-05-16T18:35:23Z

userWarnings

← Older revision		Revision as of 18:35, 16 May 2025
Line 74:		Line 74:
	A full list of exception-types can be found in the [https://docs.python.org/3/library/exceptions.html#exception-hierarchy python docs]		A full list of exception-types can be found in the [https://docs.python.org/3/library/exceptions.html#exception-hierarchy python docs]

	==~~userWarnings~~==		==Warnings==
	Warnings are a subcategory of Exceptions for problems that do not break the script. E.g. for deprecated modules.		[https://docs.python.org/3/library/warnings.html Warnings] are a subcategory of Exceptions for problems that do not break the script. E.g. for deprecated modules, division by 0 etc.

	~~Once you have seen~~ the ~~warning and have decided~~ you ~~want~~ to ~~use the code as is and not bother the end user with the warning messages you can suppress~~ the warnings ~~like~~:		After importing the warnings package you can do things like
			;warnings.simplefilter(action='ignore', category=UserWarning)
			:Ignore warnings in a specific category.
			;warnings.filterwarnings("error")
			:Turn warnings into exceptions
			;warnings.resetwarnings()
			:Reset to the default handling of warnings

			Example:
	<syntaxhighlight lang=python>		<syntaxhighlight lang=python>
	import warnings		import warnings

Hdridder: /* Exception handling */

2025-04-17T07:37:11Z

Exception handling

← Older revision		Revision as of 07:37, 17 April 2025
Line 48:		Line 48:
	NOTE: elif is not allowed here.		NOTE: elif is not allowed here.

	Specifying an exception is optional but highly recommended (Easier to ask for forgiveness than permission aka EAFP) and it is said to be faster. However, take care you don't forgive real faults.		Specifying a specific exception is optional but highly recommended (Easier to ask for forgiveness than permission aka EAFP) and it is said to be faster. However, take care you don't forgive real faults.

	If more exceptions are defined with 1 try only 1 exception block will be executed,		If more exceptions are defined with 1 try only 1 exception block will be executed,

			For reporting where the exception happened use [[Python#traceback\|traceback]]

	;except <exception> as ex		;except <exception> as ex
Line 57:		Line 59:
	;type(ex)		;type(ex)
	:The exception class		:The exception class

			;except Exception
			:Catches any exception

	;except NameError		;except NameError

Hdridder: /* Exception handling */

2023-12-19T11:12:26Z

Exception handling

← Older revision		Revision as of 11:12, 19 December 2023
Line 54:		Line 54:
	;except <exception> as ex		;except <exception> as ex
	:Puts the exception result in ex. ex.message has the reason for the exception.		:Puts the exception result in ex. ex.message has the reason for the exception.

			;type(ex)
			:The exception class

	;except NameError		;except NameError
Line 65:		Line 68:

	A full list of exception-types can be found in the [https://docs.python.org/3/library/exceptions.html#exception-hierarchy python docs]		A full list of exception-types can be found in the [https://docs.python.org/3/library/exceptions.html#exception-hierarchy python docs]


	==userWarnings==		==userWarnings==

Hdridder: /* Exception handling */

2023-10-20T08:44:46Z

Exception handling

← Older revision		Revision as of 08:44, 20 October 2023
Line 65:		Line 65:

	A full list of exception-types can be found in the [https://docs.python.org/3/library/exceptions.html#exception-hierarchy python docs]		A full list of exception-types can be found in the [https://docs.python.org/3/library/exceptions.html#exception-hierarchy python docs]


			==userWarnings==
			Warnings are a subcategory of Exceptions for problems that do not break the script. E.g. for deprecated modules.

			Once you have seen the warning and have decided you want to use the code as is and not bother the end user with the warning messages you can suppress the warnings like:
			<syntaxhighlight lang=python>
			import warnings
			...
			...
			warnings.simplefilter(action='ignore', category=UserWarning)
			<code that throws warning>
			warnings.resetwarnings()
			</syntaxhighlight>

			This way the warning settings are restored after the known one has been passed

Hdridder at 13:49, 26 May 2023

2023-05-26T13:49:23Z

← Older revision		Revision as of 13:49, 26 May 2023
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	;<code>pass</code>		;<code>pass</code>
	:No operation, use e.g. to avoid negative tests		:No operation, use e.g. to avoid negative tests
	;<code>var1 = ( x if <~~condition~~> else y )</code>		;<code>var1 = ( x if <condition1> elif <condition2> y else z )</code>
	:~~No operation, use e~~.g. ~~to avoid negative tests~~		:Different way to assign a value conditionally. () only needed if spread over more lines.

Hdridder: /* Exception handling */

2022-10-06T13:44:33Z

Exception handling

← Older revision		Revision as of 13:44, 6 October 2022
Line 42:		Line 42:
	except <exception>:		except <exception>:
	blockifexceptionisthrown		blockifexceptionisthrown
	except <exception2>:		except <exception2> as ex:
	blockifexception2isthrown		blockifexception2isthrown
	else:		else:
Line 53:		Line 53:
	If more exceptions are defined with 1 try only 1 exception block will be executed,		If more exceptions are defined with 1 try only 1 exception block will be executed,

	~~The~~ exception~~-types can be found~~ in ~~the [https://docs~~.~~python~~.~~org/3/library/exceptions~~.~~html#exception-hierarchy python docs]~~		;except <exception> as ex
			:Puts the exception result in ex. ex.message has the reason for the exception.

	;except NameError		;except NameError
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	;except IndexError		;except IndexError
	:The index does not exist in the list		:The index does not exist in the list

			A full list of exception-types can be found in the [https://docs.python.org/3/library/exceptions.html#exception-hierarchy python docs]

Hdridder: /* Exception handling */

2022-06-15T15:15:28Z

Exception handling

← Older revision		Revision as of 15:15, 15 June 2022
Line 42:		Line 42:
	except <exception>:		except <exception>:
	blockifexceptionisthrown		blockifexceptionisthrown
			except <exception2>:
			blockifexception2isthrown
	else:		else:
	~~blockifNOexceptionisthrown~~		blockif_NO_exceptionisthrown
	</syntaxhighlight>		</syntaxhighlight>
	NOTE: elif is not allowed here.		NOTE: elif is not allowed here.

	Specifying an exception is optional but highly recommended (Easier to ask for forgiveness than permission aka EAFP) and it is said to be faster. However, take care you don't forgive real faults.		Specifying an exception is optional but highly recommended (Easier to ask for forgiveness than permission aka EAFP) and it is said to be faster. However, take care you don't forgive real faults.

			If more exceptions are defined with 1 try only 1 exception block will be executed,

	The exception-types can be found in the [https://docs.python.org/3/library/exceptions.html#exception-hierarchy python docs]		The exception-types can be found in the [https://docs.python.org/3/library/exceptions.html#exception-hierarchy python docs]