Optional dependencies

MANIFEST.in

@@ -1 +1 @@
-include README.rst CHANGES.rst LICENSE.txt
+include README.rst CHANGES.rst LICENSE.txt optional.txt

composer/filters.py

@@ -6,6 +6,21 @@
 
 import os
 
+try:
+    import markdown2
+except ImportError:
+    markdown2 = False
+
+try:
+    import mako.lookup
+    import mako.template
+except ImportError:
+    mako = False
+
+
+__all__ = ['Filter', 'Markdown', 'Mako', 'MakoContainer']
+
+
 class Filter(object):
     def __init__(self, index):
         self.index = index
@@ -23,9 +38,10 @@ def __call__(self, content, route=None):
 
 class Markdown(Filter):
     def __init__(self, index, **markdown_kw):
-        super(Markdown, self).__init__(index)
+        if not markdown2:
+            raise ImportError("Markdown filter requires the 'markdown2' package to be installed.")
 
-        import markdown2
+        super(Markdown, self).__init__(index)
         self.markdowner = markdown2.Markdown(**markdown_kw).convert
 
     def __call__(self, content, route=None):
@@ -34,6 +50,9 @@ def __call__(self, content, route=None):
 
 class Mako(Filter):
     def __init__(self, index, **template_kw):
+        if not mako:
+            raise ImportError("Mako filter requires the 'Mako' package to be installed.")
+
         super(Mako, self).__init__(index)
 
         from mako.lookup import TemplateLookup
@@ -58,6 +77,9 @@ class MakoContainer(Mako):
     pipes the ``content`` into the ``body`` context variable.
     """
     def __init__(self, index, template, **lookup_kw):
+        if not mako:
+            raise ImportError("MakoContainer filter requires the 'Mako' package to be installed.")
+
         super(MakoContainer, self).__init__(index, **lookup_kw)
 
         template = os.path.relpath(self.index.absolute_path(template), '.')

optional.txt

@@ -0,0 +1,9 @@
+# Composer includes optional filters which have the following dependencies:
+#
+# Dependency:     Filters:
+
+  markdown2     # composer.filters.Markdown
+  Mako          # composer.filters.Mako, composer.filters.MakoContainer
+
+# You'll need to install the dependencies manually if you plan on using these
+# filters, else an ImportError exception will be raised during instantiation.

setup.py

@@ -47,3 +47,17 @@
       composer = composer.command:main
       """
       )
+
+
+print """
+---
+
+%s
+
+---
+
+You can install all the optional dependencies with: ::
+
+    pip install -r optional.txt
+
+""" % open('optional.txt').read().strip()