tools: Add isort linter & wrapper script.

* Add dependency upon isort for development installs
* Add centralized settings for isort to setup.cfg
* Add tools/run-isort-check script for linting
* Add note about new script to README.md

The sorting settings are set to be approximately compatible with how the
tool 'black' formats code, which at least provides a good starting
point, and would require only a small change for compatibility were we
to adopt it.

Exceptions are that black:
* would need to have a specific line-length set (not the default)
* splits long lines (multi_line_output=3), vs being compact (5)

Author: neiljp

Pipfile

@@ -21,3 +21,4 @@ zipp = "==1.0.0"  # To support Python 3.5
 pudb = "==2017.1.4"
 snakeviz = "==0.4.2"
 gitlint = "==0.10.0"
+isort = "==4.3.21"

README.md

@@ -292,6 +292,7 @@ Once you have a development environment set up, you might find the following use
 | Run all tests (including linter) | `pytest` | `pipenv run pytest` |
 | Build test coverage report | `pytest --cov-report html:cov_html --cov=./` | `pipenv run pytest --cov-report html:cov_html --cov=./` |
 | Check type annotations | `./tools/run-mypy` | `pipenv run ./tools/run-mypy` |
+| Check isort compliance | `./tools/run-isort-check` | `pipenv run ./tools/run-isort-check` |
 
 #### GitLint (optional)
 

requirements.txt

@@ -8,6 +8,7 @@ pudb==2017.1.4
 snakeviz==0.4.2
 gitlint==0.10.0
 mypy==0.740
+isort==4.3.21
 emoji==0.5.0
 urwid_readline==0.10
 beautifulsoup4==4.6.0

setup.cfg

@@ -14,6 +14,19 @@ markers =
     pep8: workaround for https://bitbucket.org/pytest-dev/pytest-pep8/issues/23/
 addopts = --pep8 -rxXs --cov=zulipterminal
 
+[tool:isort]
+# For compatibility with 'black', we'd want this to be 3
+multi_line_output=5
+include_trailing_comma=True
+force_grid_wrap=0
+use_parentheses=True
+# For compatibility with 'black' we'd want to set this consistently
+line_length=79
+# We run this in Travis on the lowest python version, and this should keep valid syntax
+atomic=True
+# This ensures compatibility with pytest-pep8
+lines_after_imports=2
+
 [mypy]
 python_version = 3.6
 mypy_path = mypy_stubs

setup.py

@@ -41,6 +41,7 @@ def long_description():
     'pudb==2017.1.4',
     'snakeviz==0.4.2',
     'gitlint>=0.10',
+    'isort==4.3.21',
 ]
 
 setup(

tools/run-isort-check

@@ -0,0 +1,17 @@
+#!/usr/bin/env python3
+
+import subprocess
+import sys
+
+cmds = ["isort"]
+
+result = subprocess.call(cmds + ["--check-only", "--diff"])
+
+if result == 0:
+    print("All files have imports sorted according to rules.")
+else:
+    print("Some files are not sorted according to rules.")
+    print("You might try '{}' to automatically fix all files.".format(" ".join(cmds)))
+    print("Alternatively try 'isort <somefiles>' to just fix specific files.")
+
+sys.exit(result)