How can I determine if findAll("<specific tag name>") didn't match a tag in XML file?

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Hi Experts,

sorry for a question,

My project requires uses specific keys to be tag name, and uses this tag name to search same tag name in a XML file.

for example:

if my XML only contains these data:

<centos>

        <name>centos</name>

        <version>7</version>

        <download-url>http://ftp.ksu.edu.tw/pub/CentOS/7/isos/x86_64/CentOS-7-x86_64-DVD-1511.iso</download-url>

</centos>

and when I uses findAll("centos") method, I can get tag = name, attrib = centos ... etc

but, I need determine if my target tag didn't exist in my xml file, if I am uses findAll("centos"), if I uses findAll("fedora"), this script seems interrupt at for statement:

for system in soup.findAll('fedora'):

I understand if findAll couldn't find a target tag, then return empty string, I trying to uses:

if element == "":

   print "Script couldn't find target tag in this file" 

but the script seems stuck in for system in soup.findAll('xxxx').

can anyone provide a solution, thanks!