[Python][CI] Add yapf formatting guidelines and run check in CI.

This follows the same setup as MLIR and NPCOMP, using yapf and the
Google style guidelines, with two-space indentation.

.github/workflows/buildAndTest.yml

@@ -94,12 +94,14 @@ jobs:
           fetch-depth: 2
           submodules: "true"
 
-      # We'll be running clang-tidy later in this flow.
-      - name: Install clang-tidy
+      # We'll be running clang-tidy, etc. later in this flow.
+      - name: Install formatting and linting tools
         run: |
           sudo apt-get install -y clang-tidy-9
           sudo update-alternatives --install /usr/bin/clang-tidy clang-tidy \
             /usr/bin/clang-tidy-9 100
+          pip3 install yapf
+          echo "Using $(yapf --version)"
 
       # --------
       # Restore LLVM from cache and build if it's not in there.
@@ -246,6 +248,13 @@ jobs:
           echo "Clang-tidy found no problems"
           exit 0
 
+      # Run yapf to check Python formatting.
+      - name: python-format
+        if: ${{ always() }}
+        run: |
+          files=$(git diff --name-only $DIFF_COMMIT | grep .py)
+          yapf --diff $files
+
       # Upload the format and tidy patches to an artifact (zip'd) associated
       # with the workflow run. Only run this on a failure.
       - name: Upload format and tidy patches

.style.yapf

@@ -0,0 +1,3 @@
+[style]
+  based_on_style = google
+  indent_width = 2

.yapfignore

@@ -0,0 +1 @@
+llvm/**/*.py

tools/esi/esi-cosim-runner.py.in

@@ -56,15 +56,18 @@ class CosimTestRunner:
         sources = []
         for line in fileReader:
             # Arguments to circt-rtl-sim, except for source files list
-            if m := re.match(r"^//\s*ARGS:(.*)$", line):
+            m = re.match(r"^//\s*ARGS:(.*)$", line)
+            if m:
                 self.args.extend(m.group(1).split())
             # SOURCES are the additional source files (if any). If specified,
             # must include the current file. These files are either absolute or
             # relative to the current file.
-            if m := re.match(r"^//\s*SOURCES:(.*)$", line):
+            m = re.match(r"^//\s*SOURCES:(.*)$", line)
+            if m:
                 sources.extend(m.group(1).split())
             # Run this Python line.
-            if m := re.match(r"^//\s*PY:(.*)$", line):
+            m = re.match(r"^//\s*PY:(.*)$", line)
+            if m:
                 self.runs.append(m.group(1).strip())
         fileReader.close()