Run python oneliner in bash script

There is no need for escaping or moving the argument to its own variable.

But, keeping it mostly the same, the following works for me:

#!/usr/bin/env bash
WS="/Users/danielbeck/Desktop"
PY_GET_MVN_VERS="from xml.dom.minidom import parse;dom = parse('${WS}/pom.xml');print [n.firstChild.data for n in dom.childNodes[0].childNodes if n.firstChild and n.tagName == 'version']"
function test_mvn {
        MVN_VER=$( python -c "${PY_GET_MVN_VERS}" )
        echo ${MVN_VER}
}
test_mvn

/Users/danielbeck/Desktop/pom.xml is the example minimal POM from the Maven docs:

<project>
  <modelVersion>4.0.0</modelVersion>
  <groupId>com.mycompany.app</groupId>
  <artifactId>my-app</artifactId>
  <version>1</version>
</project>

Output:

[u'1']

Please throw away your code and just use mine (after adjusting WS) instead of adjusting yours until it works. You have quite a few syntax errors in there.