CODEWITHSUNDEEP
pythonexception
Enkri_
Enkri_

Reputation: 161

Try-Except block in python

Here is the code that I'm running, basically it just ask the user to type in numbers and then after I type in "done", calculate the average of them:

average = 0
total = 0.0
count = 0

while True:
    num = raw_input()
    if num == "done":
    break
    try:
        int(num)
        total = total + num
        count = count + 1
    except:
        print "bad data"
average = total / count
print total, count, average

My problem is even if I type in an integer number, the except block still get executed (i.e. I get "bad data" as the output), could you tell me why is that?

Upvotes: 2

Views: 130

Answers (3)

Martin Konecny
Martin Konecny

Reputation: 59601

int(num)

This returns an integer, but you aren't re-assigning num to this integer. You need to do

num = int(num)

for that line to have effect.

Also note that you should just print the exception, to find out more information:

try:
    num_int = int(num)
    total = total + num_int
    count = count + 1
except ValueError as e:
    print e

The reason we specifically catch ValueError is because it's very good practice to catch the exceptions you are expecting (and handle that particular exception's scenario), instead of catching everything blindly.

Upvotes: 4

Ry-
Ry-

Reputation: 224903

int(num) doesn’t change num; it returns a new value. You could assign that new value back to num if you wanted to change it.

num = int(num)

It’s also a good idea to catch specific errors and move as much out of the try block as possible to avoid hiding useful exception information.

average = 0
total = 0.0
count = 0

while True:
    num = raw_input()
    if num == "done":
        break
    try:
        num = int(num)
    except ValueError:
        print "bad data"
        continue

    total += num
    count += 1

average = total / count
print total, count, average

Upvotes: 1

ShadowRanger
ShadowRanger

Reputation: 155363

int(num) doesn't convert num in place, you have to assign the result. Change the line to:

num = int(num)

and you should be golden.

Upvotes: 2

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