Merge pull request #3851 from alexrudy/pretty-newlines

Adds an explicit newline for pretty-printing.

Included:

- ``p.break_()`` inserts a hard newline in the output, maintaining the correct indentation during pretty printing.
- When the pretty printer falls back to the object's ``__repr__`` method, newlines are converted from ``\n`` to ``p.break_()`` to maintain indentation

IPython/lib/pretty.py

@@ -229,7 +229,17 b' class PrettyPrinter(_PrettyPrinterBase):'
             self.buffer.append(Breakable(sep, width, self))
             self.buffer_width += width
             self._break_outer_groups()
-
+            
+    def break_(self):
+        """
+        Explicitly insert a newline into the output, maintaining correct indentation.
+        """
+        self.flush()
+        self.output.write(self.newline)
+        self.output.write(' ' * self.indentation)
+        self.output_width = self.indentation
+        self.buffer_width = 0
+        
 
     def begin_group(self, indent=0, open=''):
         """
@@ -478,8 +488,12 b' def _default_pprint(obj, p, cycle):'
     """
     klass = getattr(obj, '__class__', None) or type(obj)
     if getattr(klass, '__repr__', None) not in _baseclass_reprs:
-        # A user-provided repr.
-        p.text(repr(obj))
+        # A user-provided repr. Find newlines and replace them with p.break_()
+        output = repr(obj)
+        for idx,output_line in enumerate(output.splitlines()):
+            if idx:
+                p.break_()
+            p.text(output_line)
         return
     p.begin_group(1, '<')
     p.pretty(klass)

IPython/lib/tests/test_pretty.py

@@ -58,6 +58,23 b' class NoModule(object):'
 
 NoModule.__module__ = None
 
+class Breaking(object):
+    def _repr_pretty_(self, p, cycle):
+        with p.group(4,"TG: ",":"):
+            p.text("Breaking(")
+            p.break_()
+            p.text(")")
+
+class BreakingRepr(object):
+    def __repr__(self):
+        return "Breaking(\n)"
+
+class BreakingReprParent(object):
+    def _repr_pretty_(self, p, cycle):
+        with p.group(4,"TG: ",":"):
+            p.pretty(BreakingRepr())
+
+
 
 def test_indentation():
     """Test correct indentation in groups"""
@@ -118,3 +135,19 b' def test_pprint_nomod():'
     """
     output = pretty.pretty(NoModule)
     nt.assert_equal(output, 'NoModule')
+    
+def test_pprint_break():
+    """
+    Test that p.break_ produces expected output
+    """
+    output = pretty.pretty(Breaking())
+    expected = "TG: Breaking(\n    ):"
+    nt.assert_equal(output, expected)
+
+def test_pprint_break_repr():
+    """
+    Test that p.break_ is used in repr
+    """
+    output = pretty.pretty(BreakingReprParent())
+    expected = "TG: Breaking(\n    ):"
+    nt.assert_equal(output, expected)
  No newline at end of file