HDP 2.6.3, Ambari, Python

I was stuck by very nasty error while installing latest HDP 2.6.3 on RedHat 7.3. Installation failed giving the following error message:

Traceback (most recent call last):
  File "/var/lib/ambari-agent/cache/custom_actions/scripts/check_host.py", line 170, in actionexecute
    installed_packages, repos = self.execute_existing_repos_and_installed_packages_check(config)
  File "/var/lib/ambari-agent/cache/custom_actions/scripts/check_host.py", line 233, in execute_existing_repos_and_installed_packages_check
    installedPackages = self.pkg_provider.all_installed_packages()
  File "/usr/lib/python2.6/site-packages/resource_management/core/providers/package/yumrpm.py", line 222, in all_installed_packages
    return self._get_installed_packages(None)
  File "/usr/lib/python2.6/site-packages/resource_management/core/providers/package/yumrpm.py", line 157, in _get_installed_packages
    packages = self._lookup_packages([AMBARI_SUDO_BINARY, "yum", "list", "installed"], "Installed Packages")
  File "/usr/lib/python2.6/site-packages/resource_management/core/providers/package/yumrpm.py", line 191, in _lookup_packages
    if items[i + 2].find('@') == 0:
IndexError: list index out of range
No handlers could be found for logger "ambari_agent.HostCheckReportFileHandler"
Traceback (most recent call last):
  File "/usr/lib/python2.6/site-packages/ambari_agent/HostCheckReportFileHandler.py", line 74, in writeHostChecksCustomActionsFile
    items.append(itemDetail['name'])
TypeError: string indices must be integers, not str

I took me some time to get to the bottom. It looked that the culprit was additional stuff attached to the end of "yum list installed".

yum-metadata-parser.x86_64        1.1.4-10.el7               @anaconda/7.3
yum-rhn-plugin.noarch             2.0.1-6.1.el7_3            @rhel-7-server-rpms
zip.x86_64                        3.0-11.el7                 @anaconda/7.3
zlib.x86_64                       1.2.7-17.el7               @anaconda/7.3
Uploading Enabled Repositories Report
Loaded plugins: product-id

Judging from the Python source code:

    for i in range(0, len(items), 3):

        if '.' in items[i]:
          items[i] = items[i][:items[i].rindex('.')]
        if items[i + 2].find('@') == 0:
          items[i + 2] = items[i + 2][1:]
        packages.append(items[i:i + 3])

    return packages

the installer is expecting a number of elements returned from "yum list" to be divided by 3 and this two lines at the end obviously break this assumption. So the solution (working) was the manual fix in /usr/lib/ambari-agent/lib/resource_management/core/providers/package/yumrpm.py. Important: in this file, not in the file specified in error stack trace:  /usr/lib/python2.6/site-packages/resource_management/core/providers/package/yumrpm.py, because the installer every time overwrites script in /usr/lib/python2.6/site-packages/resource_management/core/providers/package directory. After the fix the aforementioned piece of code looks:

     for i in range(0, len(items), 3):

        if i + 2 >= len(items) : break

        if '.' in items[i]:
          items[i] = items[i][:items[i].rindex('.')]
        if items[i + 2].find('@') == 0:
          items[i + 2] = items[i + 2][1:]
        packages.append(items[i:i + 3])

    return packages