Implemented i option (inword snippet expansion) along the line of the patch by jceb, also added his test cases

UltiSnips/python.snippets

@@ -29,7 +29,7 @@ ${4/.+/(?0:\n)/}${4/(\A\s*,\s*\Z)|,?\s*([A-Za-z_][A-Za-z0-9_]*)\s*(=[^,]*)?(,\s*
 ${2/object$|(.+)/(?1:		$0.__init__\(self\)\n\n)/}${4/(\A\s*,\s*\Z)|,?\s*([A-Za-z_][A-Za-z0-9_]*)\s*(=[^,]*)?(,\s*|$)/(?2:		self._$2 = $2\n)/g}
 endsnippet
 
-snippet .
+snippet . "self." i
 self.
 endsnippet
 

doc/UltiSnips.txt

@@ -178,6 +178,9 @@ snippet on. The options currently supported are >
        of the cursor). Default is to expand snippets at every position, even
        mitten in the line. Most of my snippets have this option set, it keeps
        UltiSnips out of the way. 
+   i   Inword expansion - normally, triggers need whitespace before them to be
+       expanded. With this option, triggers are also expanded in the middle of
+       a word.
 
 4.2 Plaintext snippets                         *UltiSnips-plaintext-snippets*
 ----------------------

plugin/UltiSnips/__init__.py

@@ -11,12 +11,24 @@ from UltiSnips.Geometry import Position
 from UltiSnips.TextObjects import *
 from UltiSnips.Buffer import VimBuffer
 
+# TODO: it doesn't make sense to have
+# this as a baseclass of a dict, since we have
+# to run through all snippets anyway
 class _SnippetDictionary(dict):
     def __init__(self, *args, **kwargs):
         dict.__init__(self, *args, **kwargs)
 
         self._extends = []
 
+    def get_matching_snippets(self, trigger):
+        """Returns all snippets matching the given trigger."""
+        rv = []
+        for l in self.values():
+            for snip in l:
+                if snip.matches(trigger):
+                    rv.append(snip)
+        return rv
+
     def extends():
         def fget(self):
             return self._extends
@@ -86,6 +98,11 @@ class Snippet(object):
     def __repr__(self):
         return "Snippet(%s,%s,%s)" % (self._t,self._d,self._opts)
 
+    def matches(self, trigger):
+        if "i" not in self._opts:
+            return trigger == self._t
+        return trigger.endswith(self._t)
+
     def overwrites_previous(self):
         return "!" in self._opts
     overwrites_previous = property(overwrites_previous)
@@ -489,6 +506,9 @@ class SnippetManager(object):
                     return True
                 raise
 
+        # Adjust before, maybe the trigger is not the complete word
+        text_before += word[:-len(snippet.trigger)]
+
         self._expect_move_wo_change = True
 
         if self._cs:
@@ -590,7 +610,7 @@ class SnippetManager(object):
         parent_results = reduce( lambda a,b: a+b,
             [ self._find_snippets(p, trigger) for p in snips.extends ], [])
 
-        return parent_results + snips.get(trigger, [])
+        return parent_results + snips.get_matching_snippets(trigger)
 
 
 UltiSnips_Manager = SnippetManager()

test.py

@@ -1075,6 +1075,30 @@ class SnippetOptions_OnlyExpandWhenWSInFront_OneWithOneWOChoose(_VimTest):
     keys = "  test" + EX + "1\n"
     wanted = "  Expand me!"
 
+
+class SnippetOptions_ExpandInwordSnippets_SimpleExpand(_VimTest):
+    snippets = (("test", "Expand me!", "", "i"), )
+    keys = "atest" + EX
+    wanted = "aExpand me!"
+class SnippetOptions_ExpandInwordSnippets_ExpandSingle(_VimTest):
+    snippets = (("test", "Expand me!", "", "i"), )
+    keys = "test" + EX
+    wanted = "Expand me!"
+class SnippetOptions_ExpandInwordSnippetsWithOtherChars_Expand(_VimTest):
+    snippets = (("test", "Expand me!", "", "i"), )
+    keys = "$test" + EX
+    wanted = "$Expand me!"
+class SnippetOptions_ExpandInwordSnippetsWithOtherChars_Expand2(_VimTest):
+    snippets = (("test", "Expand me!", "", "i"), )
+    keys = "-test" + EX
+    wanted = "-Expand me!"
+class SnippetOptions_ExpandInwordSnippetsWithOtherChars_Expand3(_VimTest):
+    snippets = (("test", "Expand me!", "", "i"), )
+    keys = "ätest" + EX
+    wanted = "äExpand me!"
+
+
+
 ######################
 # SELECTING MULTIPLE #
 ######################