Add Python library (#3)

* feat: Add minimal Python library

* doc: Fix README Python comments

* feat: Add skeleton pyproject.toml / poetry.lock

* test: Add Python README test

* feat: Add CI for Python

* docs: Update README

* chore: Add --dev deps for black, flake8, and isort

* chore: Lint / format Python code

.github/workflows/ci.yml

@@ -23,3 +23,27 @@ jobs:
       - uses: actions/checkout@v3
 
       - run: bin/cargo test --all-features --all-targets --locked
+
+  python:
+    name: Test (Python)
+    runs-on: ubuntu-latest
+    strategy:
+      matrix:
+        python-version: ["3.8", "3.9", "3.10", "3.11"]
+
+    steps:
+      - uses: actions/checkout@v3
+
+      - name: Set up Python ${{ matrix.python-version }}
+        uses: actions/setup-python@v4
+        with:
+          python-version: ${{ matrix.python-version }}
+
+      - name: Install dependencies
+        run: |
+          python -m pip install --upgrade pip
+          pip install pytest
+
+      - name: Test
+        run: |
+          pytest

.gitignore

@@ -1,3 +1,5 @@
 /.hermit
 
 /target
+__pycache__
+*.pyc

README.md

@@ -18,6 +18,15 @@ exit(Code::Forbidden);
 exit(Code::Unavailable);
 ```
 
+#### Python
+
+```python
+import exit
+
+exit.Code.Forbidden.exit()
+exit.Code.Unavailable.exit()
+```
+
 See [the complete list of exit codes](#the-codes).
 
 ### About

exit.go

@@ -24,7 +24,7 @@ const (
 // Exit Codes 80-99 are reserved for user errors.
 const (
 	// UsageError indicates that the program exited unsuccessfully
-	// because it was was used incorrectly.
+	// because it was used incorrectly.
 	//
 	// Examples: a required argument was omitted or an invalid value
 	// was supplied for a flag.

exit.py

@@ -0,0 +1,119 @@
+"""
+Defines semantic exit codes which may be used by Command Line tools to aid in
+debugging and instrumentation.
+
+This package defines exit codes in two ranges. Exit Codes 80-99 indicate a user error
+of some sort. Exit Codes 100-119 indicate software or system error of some sort.
+"""
+
+import sys
+from enum import Enum
+
+
+# Code is the exit code that is passed to the system call `exit` when the
+# program terminates. Conventionally, the value zero indicates success and all
+# other values (1-255) indicate failure.
+class Code(Enum):
+    # there doesn't really appear to be any convention about letter casing
+    # here, so I'm adopting the Go format
+
+    # Indicates that the program exited successfully.
+    OK = 0
+
+    # Indicates that the program exited unsuccessfully but gives no extra
+    # context as to what the failure was.
+    NotOK = 1
+
+    # Exit Codes 80-99 are reserved for user errors.
+
+    # Indicates that the program exited unsuccessfully because it was used
+    # incorrectly.
+    #
+    # Examples: a required argument was omitted or an invalid value was
+    # supplied for a flag.
+    UsageError = 80
+
+    # Indicates that the program exited unsuccessfully because an unrecognized
+    # subcommand was invoked.
+    #
+    # This is intended for CLI multi-tools. When you run a command that doesn't
+    # exist from the shell, the shell exits 127. This is distinct from that
+    # value in that the command itself exists but the subcommand does not (e.g.
+    # `git nope` could exit 81).
+    UnknownSubcommand = 81
+
+    # Indicates that the program exited unsuccessfully because a precondition
+    # wasn't satisfied.
+    #
+    # Examples: the user must be on a VPN before using the program or have
+    # a minimum version of some other software installed.
+    RequirementNotMet = 82
+
+    # Indicates that the program exited unsuccessfully because the user isn't
+    # authorized to perform the requested action.
+    Forbidden = 83
+
+    # Indicates that the program exited unsuccessfully because it has been
+    # migrated to a new location.
+    MovedPermanently = 84
+
+    # Exit Codes 100-119 are reserved for software or system errors.
+
+    # Indicates that the program exited unsuccessfully because of a problem in
+    # its own code.
+    #
+    # Used instead of 1 when the problem is known to be with the program's
+    # code or dependencies.
+    InternalError = 100
+
+    # Indicates that the program exited unsuccessfully because a service it
+    # depends on was not available.
+    #
+    # Examples: A local daemon or remote service did not respond, a connection
+    # was closed unexpectedly, an HTTP service responded with 503.
+    Unavailable = 101
+
+    def is_ok(self):
+        """Reports whether an exit code is okay.
+
+        Returns True if the code is 0.
+        """
+
+        return self.value == 0
+
+    def is_error(self):
+        """Reports whether an exit code is an error.
+
+        Returns True if the code is *not* 0.
+        """
+
+        return self.value != 0
+
+    def is_user_error(self):
+        """Reports whether an exit code is a user error.
+
+        Returns True if the code is in the range 80-99 and False otherwise.
+        """
+
+        return 80 <= self.value <= 99
+
+    def is_software_error(self):
+        """Reports whether an exit code is a software error.
+
+        Returns True if the code is in the range 100-119 and False otherwise.
+        """
+
+        return 100 <= self.value <= 119
+
+    def is_signal(self):
+        """Reports whether an exit code is derived from a signal.
+
+        Returns True if the code is in the range 128-255 and False if not.
+        """
+
+        return 128 < self.value < 255
+
+    def exit(self):
+        """Invoke sys.exit() with this as an exit code."""
+
+        sys.exit(self.value)