[SRU] metaphlan2 is not installable in bionic

[Impact]

 * The package of metaphlan2 is not installable in bionic.

 * The "_metaphlan2.py" file contains Python 3 source but the "postinst"
 script runs "pycompile" on the Python source files. However, "pycompile"
 only supports Python version 2. The print() function in "_metaphlan2.py"
 can be imported from the "__future__" library, but Python 2 does not
 support function annotations: These are optional in Python 3, and are
 removed from the function definitions in "_metaphlan2.py" by the patch.

[Test Case]

 * Try to install the package.

[Regression Potential]

 * This patch is already applied in Debian since ~ 10 months and in Ubuntu
 since Cosmic without any problem.

=============================================

Already reported by me and Fixed by Andreas Tille in the Debian-Med team.

Python3 syntax is used in _metaphlan2.py, but "pycompile" run by the "postinst" script only supports Python2. Fixed by adding "print()" and removing function annotations:

/usr/share/metaphlan2# diff -Naur _metaphlan2.py.dist _metaphlan2.py
--- _metaphlan2.py.dist 2018-02-07 10:43:00.000000000 +0000
+++ _metaphlan2.py 2018-06-15 16:09:30.056981110 +0100
@@ -3,7 +3,7 @@
 # This module defines the functions which run MetaPhlAn2 on
 # single and paired fastq data.

-
+from __future__ import print_function
 import subprocess as sb
 from q2_types.per_sample_sequences import SingleLanePerSampleSingleEndFastqDirFmt
 from q2_types.per_sample_sequences import SingleLanePerSamplePairedEndFastqDirFmt
@@ -24,8 +24,7 @@
     sb.run(cmd, check=True)

-def profile_single_fastq(raw_data: SingleLanePerSampleSingleEndFastqDirFmt,
- nproc: int=1) -> biom.Table:
+def profile_single_fastq(raw_data, nproc=1):
     output_biom = None

     with tempfile.TemporaryDirectory() as tmp_dir:
@@ -36,8 +35,7 @@
     return output_biom

-def profile_paired_fastq(raw_data: SingleLanePerSamplePairedEndFastqDirFmt,
- nproc: int=1) -> biom.Table:
+def profile_paired_fastq(raw_data, nproc=1):
     output_biom = None

     with tempfile.TemporaryDirectory() as tmp_dir:

ProblemType: Package
DistroRelease: Ubuntu 18.04
Package: metaphlan2 2.7.5-1 [modified: usr/share/metaphlan2/_metaphlan2.py]
ProcVersionSignature: Ubuntu 4.15.0-23.25-generic 4.15.18
Uname: Linux 4.15.0-23-generic x86_64
NonfreeKernelModules: zfs zunicode zavl icp zcommon znvpair
ApportVersion: 2.20.9-0ubuntu7.2
Architecture: amd64
Date: Fri Jun 15 15:07:54 2018
ErrorMessage: installed metaphlan2 package post-installation script subprocess returned error exit status 101
PackageArchitecture: all
Python3Details: /usr/bin/python3.6, Python 3.6.5, python3-minimal, 3.6.5-3
PythonDetails: /usr/bin/python2.7, Python 2.7.15rc1, python-minimal, 2.7.15~rc1-1
RelatedPackageVersions:
 dpkg 1.19.0.5ubuntu2
 apt 1.6.1
SourcePackage: metaphlan2
Title: package metaphlan2 2.7.5-1 [modified: usr/share/metaphlan2/_metaphlan2.py] failed to install/upgrade: installed metaphlan2 package post-installation script subprocess returned error exit status 101
UpgradeStatus: No upgrade log present (probably fresh install)