Add Black for linting backend code

.travis.yml

@@ -1,8 +1,8 @@
 dist: trusty
 language: python
 python:
-  - "2.7"
   - "3.6"
+  - "2.7"
 
 branches:
   only:
@@ -46,12 +46,14 @@ before_install:
 
 install:
   - elapsed "install"
+  - "PY3=\"$(python -c 'if __import__(\"sys\").version_info[0] > 2: print(1)')\""
   # Older versions of Pip sometimes resolve specifiers like `tf-nightly`
   # to versions other than the most recent(!).
   - pip install -U pip
   # Lint check deps.
   - pip install flake8==3.7.8
   - pip install yamllint==1.17.0
+  - if [ -n "${PY3}" ]; then pip install black==19.10b0; fi
   # TensorBoard deps.
   - pip install futures==3.1.1
   - pip install grpcio==1.24.3
@@ -87,6 +89,8 @@ before_script:
   - flake8 . --count --select=E9,F63,F7,F82 --show-source --statistics
   # Lint frontend code
   - yarn lint
+  # Lint backend code
+  - if [ -n "${PY3}" ]; then black --check .; fi
   # Lint .yaml docs files. Use '# yamllint disable-line rule:foo' to suppress.
   - yamllint -c docs/.yamllint docs docs/.yamllint
   # Make sure that IPython notebooks have valid Markdown.

pyproject.toml

@@ -0,0 +1,3 @@
+[tool.black]
+line-length = 80
+target-version = ["py27", "py36", "py37", "py38"]

tensorboard/__init__.py

@@ -12,8 +12,7 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 # ==============================================================================
-"""TensorBoard is a webapp for understanding TensorFlow runs and graphs.
-"""
+"""TensorBoard is a webapp for understanding TensorFlow runs and graphs."""
 
 from __future__ import absolute_import
 from __future__ import division
@@ -67,33 +66,36 @@
 # additional discussion.
 
 
-@lazy.lazy_load('tensorboard.notebook')
+@lazy.lazy_load("tensorboard.notebook")
 def notebook():
-  import importlib
-  return importlib.import_module('tensorboard.notebook')
+    import importlib
 
+    return importlib.import_module("tensorboard.notebook")
 
-@lazy.lazy_load('tensorboard.program')
+
+@lazy.lazy_load("tensorboard.program")
 def program():
-  import importlib
-  return importlib.import_module('tensorboard.program')
+    import importlib
+
+    return importlib.import_module("tensorboard.program")
 
 
-@lazy.lazy_load('tensorboard.summary')
+@lazy.lazy_load("tensorboard.summary")
 def summary():
-  import importlib
-  return importlib.import_module('tensorboard.summary')
+    import importlib
+
+    return importlib.import_module("tensorboard.summary")
 
 
 def load_ipython_extension(ipython):
-  """IPython API entry point.
+    """IPython API entry point.
 
-  Only intended to be called by the IPython runtime.
+    Only intended to be called by the IPython runtime.
 
-  See:
-    https://ipython.readthedocs.io/en/stable/config/extensions/index.html
-  """
-  notebook._load_ipython_extension(ipython)
+    See:
+      https://ipython.readthedocs.io/en/stable/config/extensions/index.html
+    """
+    notebook._load_ipython_extension(ipython)
 
 
 __version__ = version.VERSION

tensorboard/__main__.py

@@ -24,5 +24,5 @@
 
 del _main
 
-if __name__ == '__main__':
-  run_main()
+if __name__ == "__main__":
+    run_main()