From f285f4aaae2a54cb35157eec7058b7941fcf3802 Mon Sep 17 00:00:00 2001
From: Chris Jerdonek <chris.jerdonek@gmail.com>
Date: Sat, 20 Oct 2012 11:16:00 -0700
Subject: Address issue #130: allow string coercion to be customized.

---
 pystache/renderer.py | 35 ++++++++++++++++++++++++++++++-----
 1 file changed, 30 insertions(+), 5 deletions(-)

(limited to 'pystache/renderer.py')

diff --git a/pystache/renderer.py b/pystache/renderer.py
index 49be4a0..ff6a90c 100644
--- a/pystache/renderer.py
+++ b/pystache/renderer.py
@@ -23,11 +23,11 @@ class Renderer(object):
     A class for rendering mustache templates.
 
     This class supports several rendering options which are described in
-    the constructor's docstring.  Among these, the constructor supports
-    passing a custom partial loader.
+    the constructor's docstring.  Other behavior can be customized by
+    subclassing this class.
 
-    Here is an example of rendering a template using a custom partial loader
-    that loads partials from a string-string dictionary.
+    For example, one can pass a string-string dictionary to the constructor
+    to bypass loading partials from the file system:
 
     >>> partials = {'partial': 'Hello, {{thing}}!'}
     >>> renderer = Renderer(partials=partials)
@@ -35,6 +35,16 @@ class Renderer(object):
     >>> print renderer.render('{{>partial}}', {'thing': 'world'})
     Hello, world!
 
+    To customize string coercion (e.g. to render False values as ''), one can
+    subclass this class.  For example:
+
+        class MyRenderer(Renderer):
+            def str_coerce(self, val):
+                if not val:
+                    return ''
+                else:
+                    return str(val)
+
     """
 
     def __init__(self, file_encoding=None, string_encoding=None,
@@ -146,6 +156,20 @@ class Renderer(object):
         """
         return self._context
 
+    # We could not choose str() as the name because 2to3 renames the unicode()
+    # method of this class to str().
+    def str_coerce(self, val):
+        """
+        Coerce a non-string value to a string.
+
+        This method is called whenever a non-string is encountered during the
+        rendering process when a string is needed (e.g. if a context value
+        for string interpolation is not a string).  To customize string
+        coercion, you can override this method.
+
+        """
+        return str(val)
+
     def _to_unicode_soft(self, s):
         """
         Convert a basestring to unicode, preserving any unicode subclass.
@@ -307,7 +331,8 @@ class Renderer(object):
         engine = RenderEngine(literal=self._to_unicode_hard,
                               escape=self._escape_to_unicode,
                               resolve_context=resolve_context,
-                              resolve_partial=resolve_partial)
+                              resolve_partial=resolve_partial,
+                              to_str=self.str_coerce)
         return engine
 
     # TODO: add unit tests for this method.
-- 
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