Difference between revisions of "CSC111 Exercises with Exceptions: try/except"
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<source lang="python"> | <source lang="python"> | ||
def example1(): | def example1(): | ||
| − | x = | + | while True: |
| − | + | try: | |
| − | + | x = int( input( "enter a number: " ) ) | |
| − | + | y = int( input( "enter another number: " ) ) | |
| − | + | print( x, '/', y, '=', x/y ) | |
| − | + | break | |
| − | + | except ZeroDivisionError: | |
| + | print( "Can't divide by 0!" ) | ||
| + | except ValueError: | ||
| + | print( "That doesn't look like a number!" ) | ||
| + | except: | ||
| + | print( "something unexpected happend!" ) | ||
| + | |||
| + | |||
def example2( L ): | def example2( L ): | ||
print( "\n\nExample 2" ) | print( "\n\nExample 2" ) | ||
| + | print( "L = ", L ) | ||
sum = 0 | sum = 0 | ||
| − | for i in range( len( L ) ) | + | sumOfPairs = [] |
| − | + | try: | |
| − | + | for i in range( len( L ) ): | |
| − | + | sumOfPairs.append( L[i]+L[i+1] ) | |
| − | + | except IndexError: | |
| − | + | pass | |
| − | print( " | + | print( "sumOfPairs = ", sumOfPairs ) |
| − | def | + | def printUpperFile( fileName ): |
| − | + | try: | |
| − | + | file = open( fileName, "r" ) | |
| − | + | except FileNotFoundError: | |
| − | + | print( "***Error*** File", fileName, "not found!" ) | |
| − | + | return False | |
| − | + | ||
| − | + | for line in file: | |
| − | + | print( line.upper() ) | |
| − | + | file.close() | |
| − | + | return True | |
def main(): | def main(): | ||
| − | + | example1() | |
| + | |||
L = [ 10, 3, 5, 6, 9, 3 ] | L = [ 10, 3, 5, 6, 9, 3 ] | ||
| − | + | example2( L ) | |
| − | + | ||
| − | + | open( "doesNotExistYest.txt", "w" ).close() | |
| − | + | ||
| − | + | printUpperFile( "doesNotExistYest.txt" ): | |
| + | |||
| + | printUpperFile( "./Dessssktop/misspelled.txt" ) | ||
| + | |||
main() | main() | ||
| − | |||
</source> | </source> | ||
</onlydft> | </onlydft> | ||
Revision as of 08:11, 4 April 2014
--D. Thiebaut (talk) 09:05, 2 April 2014 (EDT)
The exercises below deal with protecting Python code that might crash with try/except statements to make the program robust.
Code in need of try/except statements
- The program below is not very robust. We can easily make it crash.
- Observe each function and see how to make it fail, or see why it will fail the way it is called
- Make the program crash. Register the XXXXError that is generated. For example, if the output of the crash looks like this:
Traceback (most recent call last): File "/Users/thiebaut/Desktop/except0.py", line 29, in <module> main() File "/Users/thiebaut/Desktop/except0.py", line 27, in main example3( [ 10, 3, 5, 6 ] ) File "/Users/thiebaut/Desktop/except0.py", line 18, in example3 sum = sum + L[i] IndexError: list index out of range
- what you are interested in is IndexError. This is the exception you want to guard your code against.
try:
........
........
except IndexError:
.........
- Verify that you have made your functions more robust to erroneous input/data.
Code
def example1():
for i in range( 3 ):
x = int( input( "enter a number: " ) )
y = int( input( "enter another number: " ) )
print( x, '/', y, '=', x/y )
def example2( L ):
print( "\n\nExample 2" )
sum = 0
sumOfPairs = []
for i in range( len( L ) ):
sumOfPairs.append( L[i]+L[i+1] )
print( "sumOfPairs = ", sumOfPairs )
print( "sumOfPairs = [", ",".join( [str(k) for k in sumOfPairs] ),"]" )
def printUpperFile( fileName ):
file = open( fileName, "r" )
for line in file:
print( line.upper() )
file.close()
def main():
example1()
L = [ 10, 3, 5, 6, 9, 3 ]
example2( L )
example2( [ 10, 3, 5, 6, "NA", 3 ] )
example3( [ 10, 3, 5, 6 ] )
printUpperFile( "doesNotExistYest.txt" )
printUpperFile( "./Dessssktop/misspelled.txt" )
main()
