add code-formatting with black for python and with clang-format for c++

.clang-format

@@ -0,0 +1,3 @@
+BasedOnStyle: LLVM
+AlwaysBreakTemplateDeclarations: Yes
+RemoveBracesLLVM: No

.github/workflows/tests.yml

@@ -34,10 +34,15 @@ jobs:
           pip install -U pip wheel
           pip install -U -c constraints.txt -r requirements-dev.txt qiskit-terra numpy scipy
         shell: bash
+      - name: Run clang-format
+        run: |
+          set -e
+          sh tools/clang-format.sh --Werror -n
+        shell: bash          
       - name: Run Lint
         run: |
           set -e
-          pycodestyle --ignore=E402,W503,W504 --max-line-length=100 qiskit_aer
+          black --check qiskit_aer test tools setup.py
           pylint -j 2 -rn qiskit_aer
   sdist:
     runs-on: ${{ matrix.platform.os }}

.pylintrc

@@ -21,7 +21,7 @@ persistent=yes
 # List of plugins (as comma separated values of python modules names) to load,
 # usually to register additional checkers.
 load-plugins=pylint.extensions.docparams, # enable checking of docstring args
-    pylint.extensions.docstyle  # basic docstring stle checks
+    pylint.extensions.docstyle,  # basic docstring style checks
 
 # Use multiple processes to speed up Pylint.
 jobs=1
@@ -33,8 +33,7 @@ unsafe-load-any-extension=no
 # A comma-separated list of package or module names from where C extensions may
 # be loaded. Extensions are loading into the active Python interpreter and may
 # run arbitrary code
-extension-pkg-whitelist=
-
+extension-pkg-allow-list=
 
 [MESSAGES CONTROL]
 
@@ -43,10 +42,10 @@ extension-pkg-whitelist=
 confidence=
 
 # Enable the message, report, category or checker with the given id(s). You can
-# either give multiple identifiers separated by comma (,) or put this option
+# either give multiple identifier separated by comma (,) or put this option
 # multiple time (only on the command line, not in the configuration file where
 # it should appear only once). See also the "--disable" option for examples.
-#enable=
+enable=use-symbolic-message-instead
 
 # Disable the message, report, category or checker with the given id(s). You
 # can either give multiple identifiers separated by comma (,) or put this
@@ -57,7 +56,8 @@ confidence=
 # --enable=similarities". If you want to run only the classes checker, but have
 # no Warning level messages displayed, use"--disable=all --enable=classes
 # --disable=W"
-disable=no-self-use,        # disabled as it is too verbose
+disable=spelling,       # way too noisy
+    no-self-use,        # disabled as it is too verbose
     fixme,              # disabled as TODOs would show up as warnings
     protected-access,   # disabled as we don't follow the public vs private
                         # convention strictly
@@ -70,8 +70,13 @@ disable=no-self-use,        # disabled as it is too verbose
     unnecessary-pass,   # allow for methods with just "pass", for clarity
     no-else-return,     # relax "elif" after a clause with a return
     docstring-first-line-empty, # relax docstring style
-    unsubscriptable-object, # pylint can't determine this for numpy types
-    bad-continuation, bad-whitespace # differences of opinion with black
+    import-outside-toplevel,
+    bad-continuation, bad-whitespace, # differences of opinion with black
+    import-error,       # overzealous with our optionals/dynamic packages
+    consider-using-f-string, # pass re-lint old commits
+    broad-exception-raised, # pass re-lint old commits
+    unsubscriptable-object # pass re-lint old commits
+
 
 
 
@@ -83,12 +88,6 @@ disable=no-self-use,        # disabled as it is too verbose
 # mypackage.mymodule.MyReporterClass.
 output-format=text
 
-# Put messages in a separate file for each module / package specified on the
-# command line instead of printing them on stdout. Reports (if any) will be
-# written in a file name "pylint_global.[txt|html]". This option is deprecated
-# and it will be removed in Pylint 2.0.
-files-output=no
-
 # Tells whether to display a full report or only the messages
 reports=yes
 
@@ -117,8 +116,8 @@ evaluation=10.0 - ((float(5 * error + warning + refactor + convention) / stateme
 # pi = the PI constant
 # op = operation iterator
 # b = basis iterator
-good-names=i,j,k,n,m,ex,v,w,x,y,z,Run,_,logger,q,c,r,qr,cr,qc,nd,pi,op,b,ar,br,dt,
-    __unittest
+good-names=a,b,i,j,k,d,n,m,ex,v,w,x,y,z,Run,_,logger,q,c,r,qr,cr,qc,nd,pi,op,b,ar,br,p,cp,dt,
+    __unittest,iSwapGate,mu
 
 # Bad variable names which should always be refused, separated by a comma
 bad-names=foo,bar,toto,tutu,tata
@@ -171,16 +170,16 @@ attr-rgx=[a-z_][a-z0-9_]{2,30}$
 attr-name-hint=[a-z_][a-z0-9_]{2,30}$
 
 # Regular expression matching correct argument names
-argument-rgx=[a-z_][a-z0-9_]{2,30}$
+argument-rgx=[a-z_][a-z0-9_]{2,30}|ax|dt$
 
 # Naming hint for argument names
 argument-name-hint=[a-z_][a-z0-9_]{2,30}$
 
 # Regular expression matching correct variable names
-variable-rgx=[a-z_][a-z0-9_]{2,30}$
+variable-rgx=[a-z_][a-z0-9_]{1,30}$
 
 # Naming hint for variable names
-variable-name-hint=[a-z_][a-z0-9_]{2,30}$
+variable-name-hint=[a-z_][a-z0-9_]{1,30}$
 
 # Regular expression matching correct class attribute names
 class-attribute-rgx=([A-Za-z_][A-Za-z0-9_]{2,30}|(__.*__))$
@@ -212,7 +211,7 @@ max-nested-blocks=5
 [FORMAT]
 
 # Maximum number of characters on a single line.
-max-line-length=100
+max-line-length=105
 
 # Regexp for a line that is allowed to be longer than the limit.
 ignore-long-lines=^\s*(# )?<?https?://\S+>?$
@@ -279,7 +278,7 @@ spelling-dict=
 spelling-ignore-words=
 
 # A path to a file that contains private dictionary; one word per line.
-spelling-private-dict-file=
+spelling-private-dict-file=.local-spellings
 
 # Tells whether to store unknown words to indicated private dictionary in
 # --spelling-private-dict-file option instead of raising a message.
@@ -296,7 +295,7 @@ ignore-mixin-members=yes
 # (useful for modules/projects where namespaces are manipulated during runtime
 # and thus existing member attributes cannot be deduced by static analysis. It
 # supports qualified module names, as well as Unix pattern matching.
-ignored-modules=matplotlib.cm,numpy.random,qiskit.providers
+ignored-modules=numpy
 
 # List of class names for which member attributes should not be checked (useful
 # for classes with dynamically set attributes). This supports the use of
@@ -333,7 +332,7 @@ callbacks=cb_,_cb
 
 # List of qualified module names which can have objects that can redefine
 # builtins.
-redefining-builtins-modules=six.moves,future.builtins,tools.compiler
+redefining-builtins-modules=six.moves,future.builtins
 
 
 [CLASSES]

CONTRIBUTING.md

@@ -18,6 +18,11 @@ please ensure that:
 1. The code follows the code style of the project and successfully
    passes the tests. For convenience, you can execute `tox` locally,
    which will run these checks and report any issues.
+
+   If your code fails the local style checks, you can use `tox -eblack`
+   and `tox -eclang` to automatically fix update the code formatting
+   in python and C++ respectively.
+
 2. The documentation has been updated accordingly. In particular, if a
    function or class has been modified during the PR, please update the
    *docstring* accordingly.
@@ -185,6 +190,24 @@ like for the current state of the repo, you can run: `tox -edocs` which will
 build all the documentation into `docs/_build/html` and the release notes in
 particular will be located at `docs/_build/html/release_notes.html`
 
+## Style and lint
+
+Qiskit Aer uses 3 tools for verify code formatting and lint checking. The
+first tool is [black](https://github.com/psf/black) which is a Python code formatting
+tool that will automatically update the code formatting to a consistent style.
+The second tool is [pylint](https://www.pylint.org/) which is a code linter
+which does a deeper analysis of the Python code to find both style issues and
+potential bugs and other common issues in Python. The third tool is
+[clang-format](https://clang.llvm.org/docs/ClangFormat.html) which is a
+C++ code formatting tool that will automatically update codes with a consitent style.
+
+You can check that your local modifications conform to the style rules
+by running `tox -elint` which will run `black`, `pylint` and `clang-format`
+to check the local code formatting and lint. If black returns a code
+formatting error you can run `tox -eblack` to automatically update the
+code formatting to conform to the style. However, if `pylint` returns
+any error you will have to fix these issues by manually updating your code.
+
 ### Development Cycle
 
 The development cycle for qiskit-aer is all handled in the open using