Add DollarFormatter and tests.

IPython/utils/tests/test_text.py

@@ -44,8 +44,7 b' def test_columnize_long():'
     out = text.columnize(items, displaywidth=size-1)
     nt.assert_equals(out, '\n'.join(items+['']))
 
-def test_eval_formatter():
-    f = text.EvalFormatter()
+def eval_formatter_check(f):
     ns = dict(n=12, pi=math.pi, stuff='hello there', os=os)
     s = f.format("{n} {n//4} {stuff.split()[0]}", **ns)
     nt.assert_equals(s, "12 3 hello")
@@ -60,10 +59,7 b' def test_eval_formatter():'
     
     nt.assert_raises(NameError, f.format, '{dne}', **ns)
 
-
-def test_eval_formatter_slicing():
-    f = text.EvalFormatter()
-    f.allow_slicing = True
+def eval_formatter_slicing_check(f):
     ns = dict(n=12, pi=math.pi, stuff='hello there', os=os)
     s = f.format(" {stuff.split()[:]} ", **ns)
     nt.assert_equals(s, " ['hello', 'there'] ")
@@ -75,9 +71,7 b' def test_eval_formatter_slicing():'
     nt.assert_raises(SyntaxError, f.format, "{n:x}", **ns)
     
 
-def test_eval_formatter_no_slicing():
-    f = text.EvalFormatter()
-    f.allow_slicing = False
+def eval_formatter_no_slicing_check(f):
     ns = dict(n=12, pi=math.pi, stuff='hello there', os=os)
     
     s = f.format('{n:x} {pi**2:+f}', **ns)
@@ -85,3 +79,25 b' def test_eval_formatter_no_slicing():'
     
     nt.assert_raises(SyntaxError, f.format, "{a[:]}")
 
+def test_eval_formatter():
+    f = text.EvalFormatter()
+    eval_formatter_check(f)
+    eval_formatter_no_slicing_check(f)
+
+def test_full_eval_formatter():
+    f = text.FullEvalFormatter()
+    eval_formatter_check(f)
+    eval_formatter_slicing_check(f)
+
+def test_dollar_formatter():
+    f = text.DollarFormatter()
+    eval_formatter_check(f)
+    eval_formatter_slicing_check(f)
+    
+    ns = dict(n=12, pi=math.pi, stuff='hello there', os=os)
+    s = f.format("$n", **ns)
+    nt.assert_equals(s, "12")
+    s = f.format("$n.real", **ns)
+    nt.assert_equals(s, "12")
+    s = f.format("$n/{stuff[:5]}", **ns)
+    nt.assert_equals(s, "12/hello")

IPython/utils/text.py

@@ -677,6 +677,38 b' class FullEvalFormatter(Formatter):'
 
         return ''.join(result)
 
+class DollarFormatter(FullEvalFormatter):
+    """Formatter allowing Itpl style $foo replacement, for names and attribute
+    access only. Standard {foo} replacement also works, and allows full
+    evaluation of its arguments.
+
+    Examples
+    --------
+    In [1]: f = DollarFormatter()
+    In [2]: f.format('{n//4}', n=8)
+    Out[2]: '2'
+    
+    In [3]: f.format('23 * 76 is $result', result=23*76)
+    Out[3]: '23 * 76 is 1748'
+    
+    In [4]: f.format('$a or {b}', a=1, b=2)
+    Out[4]: '1 or 2'
+    """
+    _dollar_pattern = re.compile("(.*)\$([\w\.]+)")
+    def parse(self, fmt_string):
+        for literal_txt, field_name, format_spec, conversion \
+                    in Formatter.parse(self, fmt_string):
+            
+            # Find $foo patterns in the literal text.
+            continue_from = 0
+            for m in self._dollar_pattern.finditer(literal_txt):
+                new_txt, new_field = m.group(1,2)
+                yield (new_txt, new_field, "", "s")
+                continue_from = m.end()
+            
+            # Re-yield the {foo} style pattern
+            yield (literal_txt[continue_from:], field_name, format_spec, conversion)
+
 
 def columnize(items, separator='  ', displaywidth=80):
     """ Transform a list of strings into a single string with columns.