add `float_precision` trait to PlainTextFormatter

* moved content of %precision into _float_precision_changed
* %precision is now 2 lines that simply sets PTF.float_precision
* added doctests for %precision
* added tests for PTF.float_precision

IPython/core/formatters.py

@@ -20,6 +20,7 b' Authors:'
 #-----------------------------------------------------------------------------
 
 # Stdlib imports
+import sys
 import abc
 # We must use StringIO, as cStringIO doesn't handle unicode properly.
 from StringIO import StringIO
@@ -27,7 +28,7 b' from StringIO import StringIO'
 # Our own imports
 from IPython.config.configurable import Configurable
 from IPython.external import pretty
-from IPython.utils.traitlets import Bool, Dict, Int, Str
+from IPython.utils.traitlets import Bool, Dict, Int, Str, CStr
 
 
 #-----------------------------------------------------------------------------
@@ -353,12 +354,64 b' class PlainTextFormatter(BaseFormatter):'
     # The newline character.
     newline = Str('\n', config=True)
 
+    # format-string for pprinting floats
+    float_format = Str('%r')
+    # setter for float precision, either int or direct format-string
+    float_precision = CStr('', config=True)
+    
+    def _float_precision_changed(self, name, old, new):
+        """float_precision changed, set float_format accordingly.
+        
+        float_precision can be set by int or str.
+        This will set float_format, after interpreting input.
+        If numpy has been imported, numpy print precision will also be set.
+        
+        integer `n` sets format to '%.nf', otherwise, format set directly.
+        
+        An empty string returns to defaults (repr for float, 8 for numpy).
+        
+        This parameter can be set via the '%precision' magic.
+        """
+        
+        if '%' in new:
+            # got explicit format string
+            fmt = new
+            try:
+                fmt%3.14159
+            except Exception:
+                raise ValueError("Precision must be int or format string, not %r"%new)
+        elif new:
+            # otherwise, should be an int
+            try:
+                i = int(new)
+                assert i >= 0
+            except ValueError:
+                raise ValueError("Precision must be int or format string, not %r"%new)
+            except AssertionError:
+                raise ValueError("int precision must be non-negative, not %r"%i)
+            
+            fmt = '%%.%if'%i
+            if 'numpy' in sys.modules:
+                # set numpy precision if it has been imported
+                import numpy
+                numpy.set_printoptions(precision=i)
+        else:
+            # default back to repr
+            fmt = '%r'
+            if 'numpy' in sys.modules:
+                import numpy
+                # numpy default is 8
+                numpy.set_printoptions(precision=8)
+        self.float_format = fmt
+
     # Use the default pretty printers from IPython.external.pretty.
     def _singleton_printers_default(self):
         return pretty._singleton_pprinters.copy()
 
     def _type_printers_default(self):
-        return pretty._type_pprinters.copy()
+        d = pretty._type_pprinters.copy()
+        d[float] = lambda obj,p,cycle: p.text(self.float_format%obj)
+        return d
 
     def _deferred_printers_default(self):
         return pretty._deferred_type_pprinters.copy()

IPython/core/magic.py

@@ -3478,58 +3478,33 b' Defaulting color scheme to \'NoColor\'"""'
             In [1]: from math import pi
         
             In [2]: %precision 3
+            Out[2]: '%.3f'
         
             In [3]: pi
             Out[3]: 3.142
         
             In [4]: %precision %i
+            Out[4]: '%i'
         
             In [5]: pi
             Out[5]: 3
         
             In [6]: %precision %e
+            Out[6]: '%e'
         
             In [7]: pi**10
             Out[7]: 9.364805e+04
         
             In [8]: %precision
+            Out[8]: '%r'
         
             In [9]: pi**10
             Out[9]: 93648.047476082982
         
         """
         
-        if '%' in s:
-            # got explicit format string
-            fmt = s
-            try:
-                fmt%3.14159
-            except Exception:
-                raise ValueError("Precision must be int or format string, not %r"%s)
-        elif s:
-            # otherwise, should be an int
-            try:
-                i = int(s)
-                assert i >= 0
-            except (ValueError, AssertionError):
-                raise ValueError("Precision must be non-negative int or format string, not %r"%s)
-            
-            fmt = '%%.%if'%i
-            if 'numpy' in sys.modules:
-                import numpy
-                numpy.set_printoptions(precision=i)
-        else:
-            # default back to repr
-            fmt = '%r'
-            if 'numpy' in sys.modules:
-                import numpy
-                # numpy default is 8
-                numpy.set_printoptions(precision=8)
-        
-        def _pretty_float(obj,p,cycle):
-            p.text(fmt%obj)
-        
         ptformatter = self.shell.display_formatter.formatters['text/plain']
-        ptformatter.for_type(float, _pretty_float)
+        ptformatter.float_precision = s
+        return ptformatter.float_format
 
 # end Magic

IPython/core/tests/test_formatters.py

@@ -1,9 +1,15 b''
 """Tests for the Formatters.
 """
 
+from math import pi
+
+try:
+    import numpy
+except:
+    numpy = None
 import nose.tools as nt
 
-from IPython.core.formatters import FormatterABC, DefaultFormatter
+from IPython.core.formatters import FormatterABC, PlainTextFormatter
 
 class A(object):
     def __repr__(self):
@@ -17,7 +23,7 b' def foo_printer(obj, pp, cycle):'
     pp.text('foo')
 
 def test_pretty():
-    f = DefaultFormatter()
+    f = PlainTextFormatter()
     f.for_type(A, foo_printer)
     nt.assert_equals(f(A()), 'foo')
     nt.assert_equals(f(B()), 'foo')
@@ -26,5 +32,43 b' def test_pretty():'
     nt.assert_equals(f(B()), 'B()')
 
 def test_deferred():
-    f = DefaultFormatter()
+    f = PlainTextFormatter()
+
+def test_precision():
+    """test various values for float_precision."""
+    f = PlainTextFormatter()
+    nt.assert_equals(f(pi), repr(pi))
+    f.float_precision = 0
+    if numpy:
+        po = numpy.get_printoptions()
+        nt.assert_equals(po['precision'], 0)
+    nt.assert_equals(f(pi), '3')
+    f.float_precision = 2
+    if numpy:
+        po = numpy.get_printoptions()
+        nt.assert_equals(po['precision'], 2)
+    nt.assert_equals(f(pi), '3.14')
+    f.float_precision = '%g'
+    if numpy:
+        po = numpy.get_printoptions()
+        nt.assert_equals(po['precision'], 2)
+    nt.assert_equals(f(pi), '3.14159')
+    f.float_precision = '%e'
+    nt.assert_equals(f(pi), '3.141593e+00')
+    f.float_precision = ''
+    if numpy:
+        po = numpy.get_printoptions()
+        nt.assert_equals(po['precision'], 8)
+    nt.assert_equals(f(pi), repr(pi))
+
+def test_bad_precision():
+    """test various invalid values for float_precision."""
+    f = PlainTextFormatter()
+    def set_fp(p):
+        f.float_precision=p
+    nt.assert_raises(ValueError, set_fp, '%')
+    nt.assert_raises(ValueError, set_fp, '%.3f%i')
+    nt.assert_raises(ValueError, set_fp, 'foo')
+    nt.assert_raises(ValueError, set_fp, -1)
+
 

IPython/core/tests/test_magic.py

@@ -387,3 +387,22 b' def doctest_who():'
     In [7]: %who_ls
     Out[7]: ['alpha', 'beta']
     """
+
+def doctest_precision():
+    """doctest for %precision
+    
+    In [1]: f = get_ipython().shell.display_formatter.formatters['text/plain']
+    
+    In [2]: %precision 5
+    Out[2]: '%.5f'
+    
+    In [3]: f.float_format
+    Out[3]: '%.5f'
+    
+    In [4]: %precision %e
+    Out[4]: '%e'
+    
+    In [5]: f(3.1415927)
+    Out[5]: '3.141593e+00'
+    """
+