From 43e931baa4b8140fe700b23af6758572a8835ce7 Mon Sep 17 00:00:00 2001
From: James Rowe <jnrowe@gmail.com>
Date: Thu, 24 Feb 2011 05:15:04 +0000
Subject: [PATCH 1/3] Make readers with external dependencies optional.

---
 pelican/readers.py | 35 +++++++++++++++++++++++++----------
 1 file changed, 25 insertions(+), 10 deletions(-)

diff --git a/pelican/readers.py b/pelican/readers.py
index 35681ac1..4e1d7b2e 100644
--- a/pelican/readers.py
+++ b/pelican/readers.py
@@ -1,12 +1,18 @@
 # -*- coding: utf-8 -*-
-from docutils import core
-from markdown import Markdown
+try:
+    from docutils import core
+
+    # import the directives to have pygments support
+    import rstdirectives
+except ImportError:
+    core = False
+try:
+    from markdown import Markdown
+except ImportError:
+    Markdown = False
 import re
 import string
 
-# import the directives to have pygments support
-import rstdirectives
-
 from pelican.utils import get_date, open
 
 
@@ -17,7 +23,12 @@ _METADATAS_PROCESSORS = {
 }
 
 
-class RstReader(object):
+class Reader(object):
+    enabled = True
+
+class RstReader(Reader):
+    enabled = bool(core)
+    extension = "rst"
 
     def _parse_metadata(self, content):
         """Return the dict containing metadatas"""
@@ -43,7 +54,9 @@ class RstReader(object):
             metadatas['title'] = title
         return content, metadatas
 
-class MarkdownReader(object):
+class MarkdownReader(Reader):
+    enabled = bool(Markdown)
+    extension = "md"
 
     def read(self, filename):
         """Parse content and metadata of markdown files"""
@@ -60,7 +73,8 @@ class MarkdownReader(object):
         return content, metadatas
 
 
-class HtmlReader(object):
+class HtmlReader(Reader):
+    extension = "html"
     _re = re.compile('\<\!\-\-\#\s?[A-z0-9_-]*\s?\:s?[A-z0-9\s_-]*\s?\-\-\>')
 
     def read(self, filename):
@@ -76,8 +90,7 @@ class HtmlReader(object):
 
 
 
-_EXTENSIONS = {'rst': RstReader, 'md': MarkdownReader, 'html': HtmlReader}  # supported formats
-
+_EXTENSIONS = dict((cls.extension, cls) for cls in Reader.__subclasses__())
 
 def read_file(filename, fmt=None):
     """Return a reader object using the given format."""
@@ -86,4 +99,6 @@ def read_file(filename, fmt=None):
     if fmt not in _EXTENSIONS.keys():
         raise TypeError('Pelican does not know how to parse %s' % filename)
     reader = _EXTENSIONS[fmt]()
+    if not reader.enabled:
+        raise ValueError("Missing dependencies for %s" % fmt)
     return reader.read(filename)

From 6fc6a4dac9f0941c99e29636d3ac83cf11f2575d Mon Sep 17 00:00:00 2001
From: James Rowe <jnrowe@gmail.com>
Date: Thu, 24 Feb 2011 05:17:05 +0000
Subject: [PATCH 2/3] Document Reader.enabled attribute usage.

---
 docs/internals.rst | 9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)

diff --git a/docs/internals.rst b/docs/internals.rst
index 80fc8661..4ff8c91c 100644
--- a/docs/internals.rst
+++ b/docs/internals.rst
@@ -40,7 +40,8 @@ method, that is returning an HTML content and some metadata.
 
 Take a look to the Markdown reader::
 
-    class MarkdownReader(object):
+    class MarkdownReader(Reader):
+        enabled = bool(Markdown)
 
         def read(self, filename):
             """Parse content and metadata of markdown files"""
@@ -59,6 +60,12 @@ Take a look to the Markdown reader::
 
 Simple isn't it ?
 
+If your new reader requires additional Python dependencies then you should wrap
+their `imports` statements in `try...except`.  Then inside the reader's class
+set the `enabled` class attribute to mark import success or failure.  This makes
+it possible for users to continue using their favourite markup method without
+needing to install modules for all the additional formats they don't use.
+
 How to implement a new generator ?
 ==================================
 

From 09f964ffcbeda804f52133e5825a39577ae27f9d Mon Sep 17 00:00:00 2001
From: James Rowe <jnrowe@gmail.com>
Date: Sat, 26 Feb 2011 16:17:20 +0000
Subject: [PATCH 3/3] Split hard and soft dependencies in getting_started doc.

---
 docs/getting_started.rst | 9 +++++----
 1 file changed, 5 insertions(+), 4 deletions(-)

diff --git a/docs/getting_started.rst b/docs/getting_started.rst
index 442732be..d90e1fe8 100644
--- a/docs/getting_started.rst
+++ b/docs/getting_started.rst
@@ -23,13 +23,14 @@ At this time, pelican is dependent of the following python packages:
 
 * feedgenerator, to generate the ATOM feeds.
 * jinja2, for templating support.
-* pygments, to have syntactic colorization
-* docutils and Markdown
 
 If you're not using python 2.7, you will also need `argparse`.
 
-All those dependencies will be processed automatically if you install pelican
-using setuptools/distribute or pip.
+Optionally:
+
+* docutils, for reST support
+* pygments, to have syntactic colorization with resT input
+* Markdown, for Markdown as an input format
 
 Writing articles using pelican
 ==============================