Exception Handling in Python programming : When programming, errors happen. It’s just the way it is. Perhaps the user gave bad input. Maybe a network resource was unavailable. Maybe the program ran out of memory. Or the programmer may have even made a mistake!
Python’s solution to errors is exceptions. You might have seen an exception before.
print(a)
The above code alone will yield the following exception in Python:
Traceback (most recent call last):
File “”, line 1, in
print (a)
NameError: name ‘a’ is not defined
Oh snap! We forgot to assign a value to the ‘a’ variable. But sometimes you don’t want exceptions to completely stop the program or even crash. You might want to do something special when an exception is raised. This is done in a try/except block.
As a great programmer you must try to make certain your program can handle user errors, or even detect errors. Usually, this is accomplished by PROPER beta testing yourself or with others.
Here’s a trivial example: Suppose you’re iterating over a list. You need to iterate over 20 numbers, but the list is made from user input, and might not have 20 numbers in it. After you reach the end of the list, you just want the rest of the numbers to be interpreted as a 0. Here’s how you could do that:
def do_stuff_with_number(n):
print(n)
the_list = (1, 2, 3, 4, 5)
for i in range(20):
try:
do_stuff_with_number(the_list[i])
except IndexError: # Raised when accessing a non-existing index of a list
do_stuff_with_number(0)
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You can do that with any exception. For more details on handling exceptions, look no further than handling exceptions in Python here.
# answer code. try exercise below.
actor = {"name": "John Cleese", "rank": "awesome"}
def get_last_name():
return actor["name"].split()[1]
get_last_name()
print("All exceptions caught! Good job!")
print("The actor's last name is %s" % get_last_name())
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