Make ENV look like a constant and not raise when keys are missing

Closes #4

Author: Jonathan Como

README.md

@@ -109,3 +109,27 @@ snake install                    # Installs dependencies
 snake build:app target={target}  # Builds the tools
 snake build:tools [typ=core]     # Builds the application
 ```
+
+## API Reference
+
+### `@task(requires=None)`
+
+Decorates a function that then exposes it as a task to be run.
+The name of the function becomes the name of the task.
+The `requires` parameter, if specified, is a list of strings where each string is the name of a task that this one depends on.
+
+### `@namespace`
+
+Decorates a function so that it exposes a task namespace.
+The name of the function becomes the name of the namespace.
+Tasks and nested namespaces can be defined in the namespace and will be called as `namespace:task`.
+
+### `sh(command, silent=False)`
+
+Runs a shell command.
+If silent is not specified, an exception will be raised if the resulting status of the command is nonzero.
+
+### `ENV`
+
+A dict that gives you access to environment variables.
+It has a special property that accessing by key using brackets will not raise a `KeyError` but will return `None` instead.

Snakefile

@@ -1,20 +1,20 @@
 from snake import *
 import os
 
-ENV = 'env'
+ENV_DIR = 'env'
 
 
 @task
 def bootstrap():
     """Bootstrap the virtualenv"""
-    if not os.path.exists(ENV):
-        sh('virtualenv -p python2.7 %s' % ENV)
+    if not os.path.exists(ENV_DIR):
+        sh('virtualenv -p python2.7 %s' % ENV_DIR)
 
 
 @task(requires=['bootstrap'])
 def install():
     """Install development dependencies"""
-    sh('%s/bin/pip install -r requirements.txt' % ENV)
+    sh('%s/bin/pip install -r requirements.txt' % ENV_DIR)
 
 
 @namespace
@@ -23,7 +23,7 @@ def test():
     @task
     def current(test=''):
         """Run tests in current virtualenv"""
-        sh('%s/bin/nosetests -s %s' % (ENV, test))
+        sh('%s/bin/nosetests -s %s' % (ENV_DIR, test))
 
     @task
     def all():

snake/__init__.py

@@ -1,3 +1,3 @@
-from .application import env, sh, task, namespace
+from .application import ENV, sh, task, namespace
 
-__all__ = ['env', 'sh', 'task', 'namespace']
+__all__ = ['ENV', 'sh', 'task', 'namespace']

snake/application.py

@@ -4,6 +4,7 @@
 from sys import exit, stderr, argv, exc_info
 from traceback import extract_tb
 
+from .datastructures import LenientDict
 from .parser import ApplicationArgsParser as parser
 from .shell import ShellWrapper
 from .tasks import TaskRegistry, NoSuchTaskException
@@ -104,7 +105,7 @@ def _execute_task(self, task, args):
 _instance = Application()
 _runner = ShellWrapper(_instance)
 
-env = environ
+ENV = LenientDict(environ)
 sh = _runner.execute
 task = _instance.registry.add_task
 namespace = _instance.registry.add_namespace

snake/datastructures.py

@@ -0,0 +1,9 @@
+class LenientDict(dict):
+    """A class describing a dict that does not raise when using bracket notation on a key that
+    does not exist. Behaves the same as a regular dict otherwise.
+    """
+    def __getitem__(self, key):
+        try:
+            return super(LenientDict, self).__getitem__(key)
+        except KeyError:
+            pass

tests/datastructures_tests.py

@@ -0,0 +1,19 @@
+from unittest2 import TestCase
+
+from snake.datastructures import LenientDict
+
+
+class LenientDictTestCase(TestCase):
+    def test_it_acts_like_dict(self):
+        d = LenientDict({'a': 1})
+        d['b'] = 2
+
+        self.assertEqual(1, d['a'])
+        self.assertEqual(2, d['b'])
+        self.assertTrue('a' in d)
+        self.assertFalse('c' in d)
+
+    def test_it_returns_nothing_instead_of_raising_for_key_error(self):
+        d = LenientDict()
+
+        self.assertIsNone(d['a'])

tests/snake_tests.py

@@ -139,13 +139,14 @@ def test_it_has_shortcut_to_current_environment(self):
 
             @task
             def check():
-                print(env.get('THING'))
+                print(ENV['THING'])
+                print(ENV['OTHER'])
         """)
 
         result = self.execute('snake check')
 
         self.assertStderrEmpty(result)
-        self.assertStdoutEqual(result, ['hey'])
+        self.assertStdoutEqual(result, ['hey', 'None'])
         self.assertStatusEqual(result, 0)
 
     def test_it_exits_when_shell_command_fails(self):