numpy · njsmith · Mar 13, 2016 · Feb 3, 2016 · seberg · Mar 6, 2016
diff --git a/doc/release/1.12.0-notes.rst b/doc/release/1.12.0-notes.rst
@@ -154,10 +154,18 @@ Deprecations
 
 Assignment of ndarray object's ``data`` attribute
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
-Assigning the 'data' attribute is an inherently unsafe operation as pointed 
+Assigning the 'data' attribute is an inherently unsafe operation as pointed
 out in gh-7083. Such a capability will be removed in the future.
 
 Unsafe int casting of the num attribute in linspace
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
-``np.linspace`` now raises DeprecationWarning when num cannot be safely 
+``np.linspace`` now raises DeprecationWarning when num cannot be safely
 interpreted as an integer.
+
+Insufficient bit width parameter to ``binary_repr``
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+If a 'width' parameter is passed into ``binary_repr`` that is insufficient to
+represent the number in base 2 (positive) or 2's complement (negative) form,
+the function used to silently ignore the parameter and return a representation
+using the minimal number of bits needed for the form in question. Such behavior
+is now considered unsafe from a user perspective and will raise an error in the future.
diff --git a/numpy/core/numeric.py b/numpy/core/numeric.py
@@ -2090,31 +2090,6 @@ def isscalar(num):
     else:
         return type(num) in ScalarType
 
-_lkup = {
-    '0':'0000',
-    '1':'0001',
-    '2':'0010',
-    '3':'0011',
-    '4':'0100',
-    '5':'0101',
-    '6':'0110',
-    '7':'0111',
-    '8':'1000',
-    '9':'1001',
-    'a':'1010',
-    'b':'1011',
-    'c':'1100',
-    'd':'1101',
-    'e':'1110',
-    'f':'1111',
-    'A':'1010',
-    'B':'1011',
-    'C':'1100',
-    'D':'1101',
-    'E':'1110',
-    'F':'1111',
-    'L':''}
-
 def binary_repr(num, width=None):
     """
     Return the binary representation of the input number as a string.
@@ -2134,8 +2109,18 @@ def binary_repr(num, width=None):
     num : int
         Only an integer decimal number can be used.
     width : int, optional
-        The length of the returned string if `num` is positive, the length of
-        the two's complement if `num` is negative.
+        The length of the returned string if `num` is positive, or the length
+        of the two's complement if `num` is negative, provided that `width` is
+        at least a sufficient number of bits for `num` to be represented in the
+        designated form.
+
+        If the `width` value is insufficient, it will be ignored, and `num` will
+        be returned in binary(`num` > 0) or two's complement (`num` < 0) form
+        with its width equal to the minimum number of bits needed to represent
+        the number in the designated form. This behavior is deprecated and will
+        later raise an error.
+
+        .. deprecated:: 1.12.0
 
     Returns
     -------
@@ -2146,6 +2131,7 @@ def binary_repr(num, width=None):
     --------
     base_repr: Return a string representation of a number in the given base
                system.
+    bin: Python's built-in binary representation generator of an integer.
 
     Notes
     -----
@@ -2169,27 +2155,43 @@ def binary_repr(num, width=None):
     The two's complement is returned when the input number is negative and
     width is specified:
 
-    >>> np.binary_repr(-3, width=4)
-    '1101'
+    >>> np.binary_repr(-3, width=3)
+    '101'
+    >>> np.binary_repr(-3, width=5)
+    '11101'
 
     """
-    # ' <-- unbreak Emacs fontification
-    sign = ''
-    if num < 0:
+    def warn_if_insufficient(width, binwdith):
+        if width is not None and width < binwidth:
+            warnings.warn(
+                "Insufficient bit width provided. This behavior "
+                "will raise an error in the future.", DeprecationWarning
+            )
+
+    if num == 0:
+        return '0' * (width or 1)
+
+    elif num > 0:
+        binary = bin(num)[2:]
+        binwidth = len(binary)
+        outwidth = (binwidth if width is None
+                    else max(binwidth, width))
+        warn_if_insufficient(width, binwidth)
+        return binary.zfill(outwidth)
+
+    else:
         if width is None:
-            sign = '-'
-            num = -num
+            return '-' + bin(-num)[2:]
+
         else:
-            # replace num with its 2-complement
-            num = 2**width + num
-    elif num == 0:
-        return '0'*(width or 1)
-    ostr = hex(num)
-    bin = ''.join([_lkup[ch] for ch in ostr[2:]])
-    bin = bin.lstrip('0')
-    if width is not None:
-        bin = bin.zfill(width)
-    return sign + bin
+            poswidth = len(bin(-num)[2:])
+            twocomp = 2**(poswidth + 1) + num
+
+            binary = bin(twocomp)[2:]
+            binwidth = len(binary)
+            outwidth = max(binwidth, width)
+            warn_if_insufficient(width, binwidth)
+            return '1' * (outwidth - binwidth) + binary
 
 def base_repr(number, base=2, padding=0):
     """

diff --git a/numpy/core/tests/test_deprecations.py b/numpy/core/tests/test_deprecations.py
@@ -579,21 +579,47 @@ def test_data_attr_assignment(self):
 
 
 class TestLinspaceInvalidNumParameter(_DeprecationTestCase):
-    """Argument to the num parameter in linspace that cannot be 
+    """Argument to the num parameter in linspace that cannot be
     safely interpreted as an integer is deprecated in 1.12.0.
 
-    Argument to the num parameter in linspace that cannot be 
-    safely interpreted as an integer should not be allowed. 
+    Argument to the num parameter in linspace that cannot be
+    safely interpreted as an integer should not be allowed.
     In the interest of not breaking code that passes
     an argument that could still be interpreted as an integer, a
-    DeprecationWarning will be issued for the time being to give 
+    DeprecationWarning will be issued for the time being to give
     developers time to refactor relevant code.
     """
     def test_float_arg(self):
         # 2016-02-25, PR#7328
         self.assert_deprecated(np.linspace, args=(0, 10, 2.5))
 
 
+class TestBinaryReprInsufficientWidthParameterForRepresentation(_DeprecationTestCase):
+    """
+    If a 'width' parameter is passed into ``binary_repr`` that is insufficient to
+    represent the number in base 2 (positive) or 2's complement (negative) form,
+    the function used to silently ignore the parameter and return a representation
+    using the minimal number of bits needed for the form in question. Such behavior
+    is now considered unsafe from a user perspective and will raise an error in the future.
+    """
+
+    def test_insufficient_width_positive(self):
+        args = (10,)
+        kwargs = {'width': 2}
+
+        self.message = ("Insufficient bit width provided. This behavior "
+                        "will raise an error in the future.")
+        self.assert_deprecated(np.binary_repr, args=args, kwargs=kwargs)
+
+    def test_insufficient_width_negative(self):
+        args = (-5,)
+        kwargs = {'width': 2}
+
+        self.message = ("Insufficient bit width provided. This behavior "
+                        "will raise an error in the future.")
+        self.assert_deprecated(np.binary_repr, args=args, kwargs=kwargs)
+
+
 class TestTestDeprecated(object):
     def test_assert_deprecated(self):
         test_case_instance = _DeprecationTestCase()

diff --git a/numpy/core/tests/test_numeric.py b/numpy/core/tests/test_numeric.py
@@ -1021,12 +1021,25 @@ class TestBinaryRepr(TestCase):
     def test_zero(self):
         assert_equal(np.binary_repr(0), '0')
 
-    def test_large(self):
-        assert_equal(np.binary_repr(10736848), '101000111101010011010000')
+    def test_positive(self):
+        assert_equal(np.binary_repr(10), '1010')
+        assert_equal(np.binary_repr(12522),
+                     '11000011101010')
+        assert_equal(np.binary_repr(10736848),
+                     '101000111101010011010000')
 
     def test_negative(self):
         assert_equal(np.binary_repr(-1), '-1')
-        assert_equal(np.binary_repr(-1, width=8), '11111111')
+        assert_equal(np.binary_repr(-10), '-1010')
+        assert_equal(np.binary_repr(-12522),
+                     '-11000011101010')
+        assert_equal(np.binary_repr(-10736848),
+                     '-101000111101010011010000')
+
+    def test_sufficient_width(self):
+        assert_equal(np.binary_repr(0, width=5), '00000')
+        assert_equal(np.binary_repr(10, width=7), '0001010')
+        assert_equal(np.binary_repr(-5, width=7), '1111011')
 
 
 class TestBaseRepr(TestCase):