format with yapf

This was already formatted with yapf, but perhaps I didn't do this
correctly. I copied the diff directly from kokoro build log this
time.

Author: lifanov

src/python/grpcio/commands.py

@@ -149,10 +149,11 @@ def check_and_update_cythonization(extensions):
         for source in extension.sources:
             base, file_ext = os.path.splitext(source)
             if file_ext == '.pyx':
-                generated_pyx_source = next((base + gen_ext for gen_ext in (
-                    '.c',
-                    '.cpp',
-                ) if os.path.isfile(base + gen_ext)), None)
+                generated_pyx_source = next(
+                    (base + gen_ext for gen_ext in (
+                        '.c',
+                        '.cpp',
+                    ) if os.path.isfile(base + gen_ext)), None)
                 if generated_pyx_source:
                     generated_pyx_sources.append(generated_pyx_source)
                 else:
@@ -194,7 +195,8 @@ def try_cythonize(extensions, linetracing=False, mandatory=True):
     return Cython.Build.cythonize(
         extensions,
         include_path=[
-            include_dir for extension in extensions
+            include_dir
+            for extension in extensions
             for include_dir in extension.include_dirs
         ] + [CYTHON_STEM],
         compiler_directives=cython_compiler_directives)
@@ -215,9 +217,10 @@ def compiler_ok_with_extra_std():
             """Test if default compiler is okay with specifying c++ version
             when invokec in C mode. GCC is okay with this, while clang is not.
             """
-            cc_test = subprocess.Popen(['cc', '-x', 'c', '-std=c++11', '-'],
-                                       stdout=subprocess.PIPE,
-                                       stderr=subprocess.PIPE)
+            cc_test = subprocess.Popen(
+                ['cc', '-x', 'c', '-std=c++11', '-'],
+                stdout=subprocess.PIPE,
+                stderr=subprocess.PIPE)
             _, cc_err = cc_test.communicate(input='int main(){return 0;}')
             return not 'invalid argument' in cc_err