How to make a long list of exceptions shorter in Python?

Question

I am new to programming and I am trying to handle errors on my web scraping program. I iterate from a product list through 3 websites (A, B and C) looking for the product's name and product's price. For example i want this output:

print(productA, priceA, productB, priceB, productC, price C)

But sometimes some products do not store let say the price or the products name because it maybe be out of stock or it just can't find it and brings an AttributeError.

Because of this, I add a long list of exceptions on my program to print "not available" in each case it can't find the item's name or price it is looking for.

try:
    print(productA, priceA, productB, priceB, productC, price C)

except AttributeError:

   try:        
       print("not available", priceA, productB, priceB, productC, price C)

   except AttributeError:

       try:        
           print(productA, "not available", productB, priceB, productC, price C)

       except AttributeError:

           try:        
               print("not available", "not available", productB, priceB, productC, price C)
...

And so on for the three products, trying to see if one, two, or the three items' name or price may be missing and bringing up the error. My question is, is there a way to make this easier/faster or automate it so the code won't be so long? Thanks

Why not keep individual product and price separately which will improve readability. Try-> for price A except something. Or do in a loop. better. Create a dict of product and iterate to find the prices of the product — mad_
– mad_, Commented Oct 8, 2018 at 15:32

mad_ · Accepted Answer · 2018-10-08 16:05:03Z

1

Simple example of implementing dictionary and iterating it over

d={'product A':'', 'product B':22, 'product C':33}

for key,value in d.items():
    try:
        print('product:{}, price:{}'.format(key,int(value)))
    except Exception:
        print('price for {} is not available'.format(key))

edited Oct 8, 2018 at 16:05

answered Oct 8, 2018 at 15:58

mad_

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Comments

vash_the_stampede · Accepted Answer · 2018-10-08 16:47:37Z

0

This is demonstration with pseudo values and using ValueError the values I assigned are irrelevant and only used to raise an Error to show how this could be done with a loop. In your code it would be AttributeError if you put all your items in a list then used a loop to print each item, and you could then just print an alternate message if the error caught. If you want everything on one line you could just add end = ' ' to your print statements

productA, priceA, priceB, productC, priceC = '1', '10', 'blah', '10', '100'

lista = [productA, priceA, priceB, productC, priceC]
for i in lista:
    try:
        print(int(i))
    except ValueError:
        print('{} is not available'.format(i))

1
10
blah is not available
10
100

edited Oct 8, 2018 at 16:47

answered Oct 8, 2018 at 15:43

vash_the_stampede

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6 Comments

mad_ Over a year ago

This assumes that product name is also int which might not be the case it could be just product A if you know what I mean

vash_the_stampede Over a year ago

@mad_ I wasn't taking any guesses as to what the contents were, I just wanted to raise any Error to show how the process would work, in the case of OP it would be Attribute Error but I could not replicate that without their values

mad_ Over a year ago

I know but this will give the wrong idea of product names. You can just keep the prices or product and price in tuple and iterate the list of tuples.

vash_the_stampede Over a year ago

@JeffLearman the purpose has nothing to do with the values I could have gone a different route made evertyhing 'z' and done int('z') for all its only purpose was to raise an Error for modeling purposes, if we look at OP her error is AttributeError the time to replicate that is muhc longer than me using false values

vash_the_stampede Over a year ago

@JeffLearman if you read I stated that, OP problem is Attribute Error not Value this is just a model

|

Jeff Learman · Accepted Answer · 2018-10-08 17:20:17Z

Consider factoring out these aspects:

name of item you're searching for
site you're searching (keep in mind you may add more sites later!)
name you find at a given site (if any)
price you find at a given site (if any)

Something like this:

products = [
    "LED flashlight",
    "AAA battery",
    "AA battery"
]

sites = {
    "Amazon" : "http://amazon.com",
    "Ebay" : "http://ebay.com",
    "Monoprice": "http:monoprice.com"
}

def my_search(url, prodname):
    # your site search code here
    # ...
    return (foundname, foundprice)

for product in products:
    for (site, url) in sites.items():
        (name, price) = my_search(url, product)
            try:
                print(name, end=' ')
            except Exception:
                print("not available", end=' ')
            try:
                print(price, end=' ')
            except Exception:
                print("not available", end=' ')
        print()

With minor changes you could easily produce an HTML or table or CSV file including column headers, that is easily modified to add sites or products. Note that my regex patterns above are NOT good regex examples!

Finally, it's a bad idea to catch Exception for logic purposes, because then you will mishandle other kinds of errors (like someone trying to abort the program if it's caught in an infinite loop.) Find out which exception you're getting and catch just that exception. Better yet, have your search method produce None or "not available" for product name or price, if it doesn't find them.

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