[kupfer] Introduce capability blocker environmental variables

[Ulrik Sverdrup <usverdrup src gnome org>]

commit 1378e4ec848192b40a5f010e1b2dbb1294490275
Author: Ulrik Sverdrup <ulrik sverdrup gmail com>
Date:   Fri Feb 5 16:29:26 2010 +0100

    Introduce capability blocker environmental variables
    
    Implement KUPFER_NO_CACHE and KUPFER_NO_CUSTOM_PLUGINS

 Documentation/Quickstart.rst |   10 ++++++++++
 kupfer/config.py             |    3 +++
 kupfer/core/sources.py       |    8 ++++++++
 kupfer/plugin/__init__.py    |    3 +++
 4 files changed, 24 insertions(+), 0 deletions(-)
---
diff --git a/Documentation/Quickstart.rst b/Documentation/Quickstart.rst
index e0c3768..77ae6f5 100644
--- a/Documentation/Quickstart.rst
+++ b/Documentation/Quickstart.rst
@@ -74,6 +74,16 @@ Custom plugins are added to kupfer by installing them to the directory
 *~/.local/share/kupfer/plugins*, or any kupfer/plugins directory in any
 of ``$XDG_DATA_DIRS``.
 
+ENVIRONMENT VARIABLES
+=====================
+
+If *KUPFER_NO_CUSTOM_PLUGINS* is set, only allow loading built-in
+plugins (installed in the program's python package).
+
+If *KUPFER_NO_CACHE* is set, do not load from or write to any source
+cache files.
+
+
 .. vim: ft=rst tw=72
 .. this document best viewed with::
         rst2pdf Quickstart.rst && xdg-open Quickstart.pdf
diff --git a/kupfer/config.py b/kupfer/config.py
index aa48bc5..c4ffa68 100644
--- a/kupfer/config.py
+++ b/kupfer/config.py
@@ -10,6 +10,9 @@ PACKAGE_NAME="kupfer"
 class ResourceLookupError (StandardError):
 	pass
 
+def has_capability(cap):
+	return not bool(os.getenv("KUPFER_NO_%s" % cap, False))
+
 def get_cache_home():
 	"""
 	Directory where cache files should be put
diff --git a/kupfer/core/sources.py b/kupfer/core/sources.py
index 8e2288c..ff7563e 100644
--- a/kupfer/core/sources.py
+++ b/kupfer/core/sources.py
@@ -83,6 +83,9 @@ class SourcePickler (pretty.OutputMixin):
 	def __init__(self):
 		self.open = lambda f,mode: gzip.open(f, mode, compresslevel=3)
 
+	def should_use_cache(self):
+		return config.has_capability("CACHE")
+
 	def rm_old_cachefiles(self):
 		"""Checks if there are old cachefiles from last version,
 		and deletes those
@@ -117,6 +120,9 @@ class SourcePickler (pretty.OutputMixin):
 		return os.path.join(config.get_cache_home(), filename)
 
 	def unpickle_source(self, source):
+		if not self.should_use_cache():
+			return None
+
 		cached = self._unpickle_source(self.get_filename(source))
 		if not cached:
 			return None
@@ -143,6 +149,8 @@ class SourcePickler (pretty.OutputMixin):
 		return source
 
 	def pickle_source(self, source):
+		if not self.should_use_cache():
+			return None
 		return self._pickle_source(self.get_filename(source), source)
 	def _pickle_source(self, pickle_file, source):
 		"""
diff --git a/kupfer/plugin/__init__.py b/kupfer/plugin/__init__.py
index efa5fdd..b5cb1a5 100644
--- a/kupfer/plugin/__init__.py
+++ b/kupfer/plugin/__init__.py
@@ -5,6 +5,9 @@ def _extend_path():
 	from kupfer import config
 	from kupfer import pretty
 
+	if not config.has_capability("CUSTOM_PLUGINS"):
+		return
+
 	# Add plugins in data directories
 	__path__.extend(config.get_data_dirs("plugins"))