lint: Use black and isort for py files.

Author: PIG208

.flake8

@@ -2,6 +2,10 @@
 ignore =
     # Each of these rules are ignored for the explained reason.
 
+    # "whitespace before ':'"
+    # Black disagrees with this.
+    E203,
+
     # "multiple spaces before operator"
     # There are several typos here, but also several instances that are
     # being used for alignment in dict keys/values using the `dict`

pyproject.toml

@@ -0,0 +1,9 @@
+[tool.black]
+line-length = 100
+target-version = ["py36"]
+
+[tool.isort]
+src_paths = [".", "tools"]
+known_third_party = "zulip"
+profile = "black"
+line_length = 100

requirements.txt

@@ -1,6 +1,8 @@
 crayons
 twine
 coverage>=4.4.1
+black
+isort
 flake8
 mock
 pytest

tools/lint

@@ -2,6 +2,7 @@
 
 import argparse
 import sys
+import re
 
 from zulint.command import add_default_linter_arguments, LinterConfig
 
@@ -28,6 +29,14 @@ def run() -> None:
                                   description="Standard Python linter (config: .flake8)")
     linter_config.external_linter('gitlint', ['tools/lint-commits'],
                                   description="Git Lint for commit messages")
+    linter_config.external_linter("isort", ["isort"], ["py"],
+                                  description="Sorts Python import statements",
+                                  check_arg=["--check-only", "--diff"])
+    linter_config.external_linter("black", ["black"], ["py"],
+                                  description="Reformats Python code",
+                                  check_arg=["--check"],
+                                  suppress_line=lambda line: line == "All done! ✨ 🍰 ✨\n"
+                                  or re.fullmatch(r"\d+ files? would be left unchanged\.\n", line) is not None)
 
     @linter_config.lint
     def custom_py() -> int: