Drop support for Python 3.6 (#7295)

* Drop support for Python 3.6

As has been advertised for some time the Qiskit 0.19.0 release is the
last release which supports Python 3.6 (which goes End of Life in
Decemeber). This commit drops support accordingly so that the minimum
supported Python version is 3.7.

* Add release note

azure-pipelines.yml

@@ -28,7 +28,7 @@ stages:
       variables:
         python.version: '3.7'
         CIBW_BEFORE_BUILD: pip install -U Cython
-        CIBW_SKIP: cp27-* cp34-* cp35-* pp*
+        CIBW_SKIP: cp27-* cp34-* cp35-* cp36-* pp*
         TWINE_USERNAME: qiskit
         CIBW_TEST_COMMAND: python {project}/examples/python/stochastic_swap.py
       steps:
@@ -72,7 +72,7 @@ stages:
       variables:
         python.version: '3.7'
         CIBW_BEFORE_BUILD: pip install -U Cython
-        CIBW_SKIP: cp27-* cp34-* cp35-* pp*
+        CIBW_SKIP: cp27-* cp34-* cp35-* cp36-* pp*
         TWINE_USERNAME: qiskit
         CIBW_TEST_COMMAND: python {project}/examples/python/stochastic_swap.py
       steps:
@@ -96,7 +96,7 @@ stages:
       variables:
         python.version: '3.7'
         CIBW_BEFORE_BUILD: pip install -U Cython
-        CIBW_SKIP: cp27-* cp34-* cp35-* pp*
+        CIBW_SKIP: cp27-* cp34-* cp35-* cp36-* pp*
         CIBW_ARCHS_MACOS: universal2
         TWINE_USERNAME: qiskit
         CIBW_TEST_COMMAND: python {project}/examples/python/stochastic_swap.py
@@ -120,12 +120,10 @@ stages:
       condition: startsWith(variables['Build.SourceBranch'], 'refs/tags')
       variables:
         CIBW_BEFORE_BUILD: pip install -U Cython
-        CIBW_SKIP: cp27-* cp34-* cp35-* pp*
+        CIBW_SKIP: cp27-* cp34-* cp35-* cp36-* pp*
         TWINE_USERNAME: qiskit
         CIBW_TEST_COMMAND: python {project}\examples\python\stochastic_swap.py
       steps:
-        - {task: UsePythonVersion@0, inputs: {versionSpec: '3.6', architecture: x86}}
-        - {task: UsePythonVersion@0, inputs: {versionSpec: '3.6', architecture: x64}}
         - {task: UsePythonVersion@0, inputs: {versionSpec: '3.7', architecture: x86}}
         - {task: UsePythonVersion@0, inputs: {versionSpec: '3.7', architecture: x64}}
         - {task: UsePythonVersion@0, inputs: {versionSpec: '3.8', architecture: x86}}
@@ -506,8 +504,6 @@ stages:
       pool: {vmImage: 'windows-latest'}
       strategy:
         matrix:
-          Python36:
-            python.version: '3.6'
           Python38:
             python.version: '3.8'
           Python39:
@@ -587,8 +583,6 @@ stages:
       pool: {vmImage: 'ubuntu-latest'}
       strategy:
         matrix:
-          Python36:
-            python.version: '3.6'
           Python38:
             python.version: '3.8'
           Python39:
@@ -671,8 +665,6 @@ stages:
       pool: {vmImage: 'macOS-10.15'}
       strategy:
         matrix:
-          Python36:
-            python.version: '3.6'
           Python38:
             python.version: '3.8'
           Python39:

qiskit/__init__.py

@@ -58,14 +58,6 @@ from .version import QiskitVersion  # noqa
 __qiskit_version__ = QiskitVersion()
 
 
-if sys.version_info < (3, 7):
-    warnings.warn(
-        "Using Qiskit with Python 3.6 is deprecated as of qiskit-terra 0.17.0. "
-        "Support for running Qiskit with Python 3.6 will be removed in qiskit-terra 0.20.0.",
-        DeprecationWarning,
-    )
-
-
 class AerWrapper:
     """Lazy loading wrapper for Aer provider."""
 

releasenotes/notes/drop-python3.6-support-45ecc9e1832934cd.yaml

@@ -0,0 +1,5 @@
+---
+upgrade:
+  - |
+    Support for running with Python 3.6 has been removed. To run Qiskit you need
+    a minimum Python version of 3.7.

requirements.txt

@@ -10,7 +10,3 @@ python-dateutil>=2.8.0
 stevedore>=3.0.0
 symengine>=0.8 ; platform_machine == 'x86_64' or platform_machine == 'aarch64' or platform_machine == 'ppc64le' or platform_machine == 'amd64' or platform_machine == 'arm64'
 tweedledum>=1.1,<2.0
-
-# remove these once support for python 3.6 is dropped
-dataclasses>=0.8;python_version<'3.7'
-contextvars>=2.4;python_version<'3.7'

setup.py

@@ -112,7 +112,6 @@ setup(
         "Operating System :: MacOS",
         "Operating System :: POSIX :: Linux",
         "Programming Language :: Python :: 3 :: Only",
-        "Programming Language :: Python :: 3.6",
         "Programming Language :: Python :: 3.7",
         "Programming Language :: Python :: 3.8",
         "Programming Language :: Python :: 3.9",
@@ -123,7 +122,7 @@ setup(
     install_requires=REQUIREMENTS,
     setup_requires=["Cython>=0.27.1"],
     include_package_data=True,
-    python_requires=">=3.6",
+    python_requires=">=3.7",
     extras_require={
         "visualization": visualization_extras,
         "bip-mapper": bip_requirements,

tox.ini

@@ -1,6 +1,6 @@
 [tox]
 minversion = 2.1
-envlist = py36, py37, py38, lint-incr
+envlist = py37, py38, py39, lint-incr
 skipsdist = True
 
 [testenv]