Allow disabling of dependency installation in setup.py

CONTRIBUTING.md

@@ -372,6 +372,11 @@ the `dist/` directory, so next step is installing it:
 
     qiskit-aer/dist$ pip install -U dist/qiskit_aer*.whl
 
+As we are using *scikit-build* and we need some *Python* dependencies to be present before compiling the C++ code, 
+we install those dependencies outside the regular setuptools *mechanism*. If you want to avoid automatic installation 
+of these packages set the environment variable DISABLE_DEPENDENCY_INSTALL (ON or 1).
+
+
 **Standalone Executable**
 
 If we want to build a standalone executable, we have to use *CMake* directly.
@@ -465,6 +470,10 @@ the `dist/` directory, so next step is installing it:
 
     qiskit-aer/dist$ pip install -U dist/qiskit_aer*.whl
 
+As we are using *scikit-build* and we need some *Python* dependencies to be present before compiling the C++ code,
+we install those dependencies outside the regular setuptools *mechanism*. If you want to avoid automatic installation
+of these packages set the environment variable DISABLE_DEPENDENCY_INSTALL (ON or 1).
+
 **Standalone Executable**
 
 If we want to build a standalone executable, we have to use **CMake** directly.
@@ -564,6 +573,10 @@ the `dist/` directory, so next step is installing it:
 
     (QiskitDevEnv) qiskit-aer\dist$ pip install -U dist\qiskit_aer*.whl
 
+As we are using *scikit-build* and we need some *Python* dependencies to be present before compiling the C++ code,
+we install those dependencies outside the regular setuptools *mechanism*. If you want to avoid automatic installation
+of these packages set the environment variable DISABLE_DEPENDENCY_INSTALL (ON or 1).
+
 **Standalone Executable**
 
 If we want to build a standalone executable, we have to use **CMake** directly.

releasenotes/notes/avoid-dependency-install-7d782ed5c8965629.yaml

@@ -0,0 +1,6 @@
+---
+features:
+  - |
+    Some *Python* packages needed at C++ compilaton step were installed outside the regular *setuptools* circuit,
+    and it was not possible to avoid their installation by any option. Now it is possible to avoid automatic
+    installation of those packages by setting the environment variable *DISABLE_DEPENDENCY_INSTALL* to *1* or *ON*.

setup.py

@@ -10,29 +10,41 @@
 import setuptools
 import subprocess
 import sys
+from pkg_resources import parse_version
 import platform
 
 
 PACKAGE_NAME = os.getenv('QISKIT_AER_PACKAGE_NAME', 'qiskit-aer')
 _DISABLE_CONAN = distutils.util.strtobool(os.getenv("DISABLE_CONAN", "OFF").lower())
+_DISABLE_DEPENDENCY_INSTALL = distutils.util.strtobool(os.getenv("DISABLE_DEPENDENCY_INSTALL", "OFF").lower())
+
+def install_needed_req(to_import, to_install=None, min_version=None, max_version=None):
+    to_install = to_install if to_install else to_import
+    to_install_ver = to_install
+    to_install_ver = to_install_ver + '>=' + min_version if min_version else to_install_ver
+    to_install_ver = to_install_ver + '<' + max_version if max_version else to_install_ver
 
-if not _DISABLE_CONAN:
     try:
-        from conans import client
-    except ImportError:
-        subprocess.call([sys.executable, '-m', 'pip', 'install', 'conan>=1.31.2'])
-        from conans import client
-
-try:
-    from skbuild import setup
-except ImportError:
-    subprocess.call([sys.executable, '-m', 'pip', 'install', 'scikit-build'])
-    from skbuild import setup
-
-try:
-    import pybind11
-except ImportError:
-    subprocess.call([sys.executable, '-m', 'pip', 'install', 'pybind11>=2.6'])
+        mod = importlib.import_module(to_import)
+        mod_ver = parse_version(mod.__version__)
+        if ((min_version and mod_ver < parse_version(min_version))
+                or (max_version and mod_ver >= parse_version(max_version))):
+            raise RuntimeError('{} {} is installed but required version is {}.'.
+                               format(to_install, mod_ver, to_install_ver))
+
+    except ImportError as err:
+        if _DISABLE_DEPENDENCY_INSTALL:
+            raise ImportError(str(err) +
+                              "\n{} is a required dependency. Please provide it and repeat install"
+                              .format(to_install))
+
+        subprocess.call([sys.executable, '-m', 'pip', 'install', to_install_ver])
+
+if not _DISABLE_CONAN:
+    install_needed_req('conans', to_install='conan', min_version='1.31.2')
+
+install_needed_req('skbuild', to_install='scikit-build')
+install_needed_req('pybind11', min_version='2.6')
 
 from skbuild import setup