Exception handling3.pdf

Python

1. Chapter 3
Exception handling
New
syllabus
2023-24
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2. Exception Handling
ErrorinPythoncanbeoftwotypesi.e.Syntax
errorsandExceptions.Errorsareproblemsina
programduetowhichwillstoptheprogramfrom
execution.Ontheotherhand,exceptionsareraised
whensomeinternaleventsoccurduetolimitation
ofhardwareorsoftwarepart,whichchangethe
normalflowoftheprogram.
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3. Differenttypesofexceptionsinpython:
•SyntaxError:Thisexceptionisraisedwhentheinterpreterencountersasyntaxerrorin
thecode,suchasamisspelledkeyword,amissingcolon,oranunbalancedparenthesis.
•TypeError:Thisexceptionisraisedwhenanoperationorfunctionisappliedtoanobject
ofthewrongtype,suchasaddingastringtoaninteger.
•NameError:Thisexceptionisraisedwhenavariableorfunctionnameisnotfoundin
thecurrentscope.
•IndexError:Thisexceptionisraisedwhenanindexisoutofrangeforalist,tuple,or
othersequencetypes.
•KeyError:Thisexceptionisraisedwhenakeyisnotfoundinadictionary.
•ValueError:Thisexceptionisraisedwhenafunctionormethodiscalledwithaninvalid
argumentorinput,suchastryingtoconvertastringtoanintegerwhenthestringdoes
notrepresentavalidinteger.
•AttributeError:Thisexceptionisraisedwhenanattributeormethodisnotfoundonan
object,suchastryingtoaccessanon-existentattributeofaclassinstance.
•IOError:ThisexceptionisraisedwhenanI/Ooperation,suchasreadingorwritinga
file,failsduetoaninput/outputerror.
•ZeroDivisionError:Thisexceptionisraisedwhenanattemptismadetodivideanumber
byzero.
•ImportError:Thisexceptionisraisedwhenanimportstatementfailstofindorloada
module.
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4. DifferencebetweenSyntaxErrorand
Exceptions
SyntaxError:Thiserroriscausedbythewrongsyntaxinthe
code.
if(amount>999)
print(“amountmorethan1000")
if(amount>999)
Exceptions:Exceptionsareraisedwhentheprogramissyntactically
correct,butthecoderesultsinanerror.Thiserrordoesnotstopthe
executionoftheprogram,however,itchangesthenormalflowofthe
program.
a=10/0
print(a)
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5. handlingexceptionsusingtry-except-
finallyblocks
try:
#SomeCode....whichmayhaveruntimeerror
except:
#optionalblock
#Handlingofexception(ifrequired)
else:
#executeifnoexception
finally:
#Somecode.....(alwaysexecuted)
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6. try:
k=9//0#raisesdividebyzeroexception.
print(k)
#handleszerodivisionexception
exceptZeroDivisionError:
print("Can'tdividebyzero")
finally:
#thisblockisalwaysexecuted
#regardlessofexceptiongeneration.
print('Thisisalwaysexecuted')
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7. AdvantagesofExceptionHandling:
•Improvedprogramreliability
•Simplifiederrorhandling
•Cleanercode
•Easierdebugging
DisadvantagesofExceptionHandling:
•Performanceoverhead
•Increasedcodecomplexity
•Possiblesecurityrisks
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