import sys
# check value, if value is wrong give error message and stop program
x = -2
if x<0:
raise ValueError('x must be a positive number')
try:
a block of commands
except ErrorType: (error exceptions) in case of error
do additional commands related to error-type to handle the error without stopping the program
# wait as long as the input is not a number
while True:
try:
x = int(input("Please enter a number: "))
break
except ValueError:
print("Oops! That was no valid number. Try again...")
# in case of error, give additional error message and stop using 'raise'
try:
x=10/0
except Exception as err:
print('Error:',err)
print('Error in setting x value')
raise
Error: division by zero
Error in setting x value
Traceback (most recent call last):
File "testing_raise.py", line 15, in <module>
x=10/0
ZeroDivisionError: division by zero
# stop controlled by using sys.exit() to reduce error messages
try:
x=10/0
except Exception as err:
print('Error:',err)
print('Error in setting x value')
sys.exit(1)
Error: division by zero
Error in setting x value
# same but continue even in case of error (no stop command)
try:
x=10/0
except Exception as err:
print('Error:',err)
print('Error in setting x value')
print('continue..')
Error: division by zero
Error in setting x value
continue..
# repr(err) provides more details than print(err) → repr() str() print()
print(err)
division by zero
repr(err)
"ZeroDivisionError('division by zero',)"
# catch multiple error types
try:
s=['a','b','c']
x=int(s[6])
except (IndexError, ValueError) as err:
repr(err)
"IndexError('list index out of range',)"
# catch multiple error types, one by one
try:
s=['a','b','c']
x=int(s[6])
except ValueError as err:
repr(err)
except IndexError as err:
repr(err)
"IndexError('list index out of range',)"
Error types and exceptions
https://docs.python.org/3/tutorial/errors.html
https://docs.python.org/3/library/exceptions.html