Method 'hasattr' not testing property correctly?

Question

I'm really stuck with this! I'm getting some product data from Amazon, which is returned as an XML. When the search keyword is valid, it returns the XML with nodes Items > Item. With a wrong keyword, or a keyword that doesn't return valid results, the Item node is absent. I'm using some function to convert this XML to Object for easy parsing. Then use hasattr to recursively check various nodes.

data = someXMLConverter(xml)

#works
if hasattr(data, 'Items'):
    #doesn't work
    if hasattr(data.Items, 'Item'):
        #some processing here
    else:
        return 'Error'
else:
    return 'Error'

Even when the Item node is absent, hasattr returns true. So in case of an error, my site explodes!

Any ideas?

Sample XML:

<ItemSearchResponse>
    <OperationRequest>
        <HTTPHeaders><Header Name="UserAgent" Value="Mozilla/5.0 (Windows NT 6.1; WOW64; rv:20.0) Gecko/20100101 Firefox/20.0"/></HTTPHeaders>
        <RequestId>a393e9db-b86e-41de-965d-922c947056ff</RequestId>
        <Arguments>
            <Argument Name="Operation" Value="ItemSearch"/>
            <Argument Name="Service" Value="AWSECommerceService"/>
            <Argument Name="Signature" Value="z/R9HjzqukC6J53bmF4LPxh/xtlwBv9k+u6QjGsgFmA="/>
            <Argument Name="ItemPage" Value="1"/>
            <Argument Name="AssociateTag" Value="rutwsblog-20"/>
            <Argument Name="Version" Value="2006-09-11"/>
            <Argument Name="Keywords" Value="dggd"/>
            <Argument Name="AWSAccessKeyId" Value="AKIAJ3TAUM7ANQFQYP7Q"/>
            <Argument Name="Timestamp" Value="2013-05-17T16:50:55"/>
            <Argument Name="ResponseGroup" Value="Medium"/>
            <Argument Name="SearchIndex" Value="Books"/>
        </Arguments>
        <RequestProcessingTime>0.0217790000000000</RequestProcessingTime>
    </OperationRequest>
    <Items>
        <Request>
            <IsValid>True</IsValid>
            <ItemSearchRequest>
                <ItemPage>1</ItemPage>
                <Keywords>dggd</Keywords>
                <ResponseGroup>Medium</ResponseGroup>
                <SearchIndex>Books</SearchIndex>
            </ItemSearchRequest>
            <Errors>
                <Error>
                    <Code>AWS.ECommerceService.NoExactMatches</Code>
                    <Message>We did not find any matches for your request.</Message>
                </Error>
            </Errors>
        </Request>
        <TotalResults>0</TotalResults>
        <TotalPages>0</TotalPages>
            <MoreSearchResultsUrl>http://www.amazon.com/gp/redirect.html?camp=2025&creative=386001&location=http%3A%2F%2Fwww.amazon.com%2Fgp%2Fsearch%3Fkeywords%3Ddggd%26url%3Dsearch-alias%253Dstripbooks&linkCode=xm2&tag=xxxx-20&SubscriptionId=xxxx</MoreSearchResultsUrl>
    </Items>
</ItemSearchResponse>

What types of objects are these? In other words, what XML API are you using? — Martijn Pieters, May 17 '13 at 17:16
What is the exact code and traceback? It could be your analysis of what happens is incorrect. — Martijn Pieters, May 17 '13 at 17:16
Not an API, but some custom function I found on a site. 2 years back when I made the application, I couldn't find any library that converts Amazon's XML correctly! — Rutwick Gangurde, May 17 '13 at 17:17
Then share that function. `hasattr()` works just fine, normally, it is impossible to tell you what is going wrong in your case without more code. — Martijn Pieters, May 17 '13 at 17:18
Tried that, even the printed format show no 'Items'. I can give a screenshot if you want. — Rutwick Gangurde, May 17 '13 at 17:23
We don't want to hear that you tried it, we want to *see the output of that command* so we can help you! — kindall, May 17 '13 at 17:25
I know mate! I could give you the Amazon XML url, but the URL has a timestamp which'll expire by the time you read it! Hence I'm making a paste... — Rutwick Gangurde, May 17 '13 at 17:27
I'm suspecting that your `data.Items.Item` is `None` rather than not existent. Make sure of this. — Wessie, May 17 '13 at 17:31
I want to see your code and traceback, as text. You can also include a sample of the Amazon XML response itself (*not* the URL). — Martijn Pieters, May 17 '13 at 17:32
@Wessie Yes. It doesn't exist in the object, and the error thrown by GAE shows 'NoneType'. So how do I check for this? — Rutwick Gangurde, May 17 '13 at 17:34
Check my question description, I've created a sample of the XML. — Rutwick Gangurde, May 17 '13 at 17:40
@MartijnPieters I'm getting the NoneType error! The code is too big man! — Rutwick Gangurde, May 17 '13 at 17:47
Thanks for the help guys, but checking the node against 'None' worked. — Rutwick Gangurde, May 17 '13 at 17:53
Next time include the error at the start then; the traceback and exception would have led to solution much more quickly. — Martijn Pieters, May 17 '13 at 17:58

score 2 · Accepted Answer · answered May 17 '13 at 17:37

2

You can use the following to avoid also processing when you get None

data = someXMLConverter(xml)

if hasattr(data, 'Items'):
    if hasattr(data.Items, 'Item') and data.Items.Item is not None:
        #some processing here
    else:
        return 'Error'
else:
    return 'Error'

Since the if statement is short-circuited if hasattr returns False we can safely check for None right after.

answered May 17 '13 at 17:37

Wessie

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I'll try this, meanwhile you can check the erroneous XML pasted in my question above. – Rutwick Gangurde May 17 '13 at 17:40
Man you're my hero! This solved my issue! Thanks, my job depends on this ;) – Rutwick Gangurde May 17 '13 at 17:52

Method 'hasattr' not testing property correctly?

1 Answers1