Added __format__ method

.travis.yml

@@ -4,13 +4,18 @@ notifications:
 branches:
     only:
         - master
+        - format-method
 after_success:
     - coveralls
 matrix:
   include:
     - python: "2.7"
       env: CI=ci2
-    - python: "3.3"
+    - python: "3.4"
+      env: CI=ci3
+    - python: "3.5"
+      env: CI=ci3
+    - python: "3.6"
       env: CI=ci3
 script: make $CI
 install: ""

bitmath/__init__.py

@@ -413,6 +413,19 @@ def __str__(self):
         global format_string
         return self.format(format_string)
 
+    def __format__(self, format_spec):
+        """String representation of this object with custom formatting, such as specified number of digits."""
+        global format_string
+        try:
+            # replace any format spec added into global format_string with the format_spec used in this invocation
+            value_end = format_string.index('{value') + 6
+            brace_index = format_string.index('}', value_end)
+            format_string_custom = format_string[:value_end] + ':' + format_spec + format_string[brace_index:]
+        except ValueError:
+            # no {value} found in format_string, so cannot customize; fall back to global format_string
+            format_string_custom = format_string
+        return self.format(format_string_custom)
+
     def format(self, fmt):
         """Return a representation of this instance formatted with user
 supplied syntax"""

setup.py

@@ -59,9 +59,9 @@
         'Programming Language :: Python :: 2.6',
         'Programming Language :: Python :: 2.7',
         'Programming Language :: Python :: 3',
-        'Programming Language :: Python :: 3.1',
-        'Programming Language :: Python :: 3.2',
-        'Programming Language :: Python :: 3.3',
+        'Programming Language :: Python :: 3.4',
+        'Programming Language :: Python :: 3.5',
+        'Programming Language :: Python :: 3.6',
         'Programming Language :: Python',
         'Topic :: Scientific/Engineering :: Mathematics',
         'Topic :: Software Development :: Libraries :: Python Modules',

tests/test_representation.py

@@ -146,3 +146,39 @@ def test_print_byte_singular(self):
         one_Byte = bitmath.Byte(1.0)
         actual_result = one_Byte.format(fmt_str)
         self.assertEqual(expected_result, actual_result)
+
+    def test_inline_format(self):
+        """Inline string formatting interpolates default format_string values"""
+        expected_result = 'size: 3.1215 MiB'
+        size = bitmath.MiB(3.1215)
+        actual_result = 'size: {size}'.format(size=size)
+        self.assertEqual(expected_result, actual_result)
+
+    def test_inline_format_customized(self):
+        """Inline formats obey inline format specifications"""
+        expected_result = 'size: 3.1 MiB'
+        size = bitmath.MiB(3.1215)
+        actual_result = 'size: {size:.1f}'.format(size=size)
+        self.assertEqual(expected_result, actual_result)
+
+    def test_inline_format_override(self):
+        """Inline formats use module defaults, overriding only format spec"""
+        orig_fmt_str = bitmath.format_string
+        bitmath.format_string = "{unit} {value:.3f}"
+        expected_result = 'size: MiB 3.1'
+        size = bitmath.MiB(3.1215)
+        actual_result = 'size: {size:.1f}'.format(size=size)
+        self.assertEqual(expected_result, actual_result)
+        bitmath.format_string = orig_fmt_str
+
+    def test_inline_format_cant_override(self):
+        """Inline formats use module defaults, changing nothing if no {value} component"""
+        orig_fmt_str = bitmath.format_string
+        bitmath.format_string = "{power} {binary}"
+        expected_result = 'size: 20 0b1100011111000110101001111'
+        size = bitmath.MiB(3.1215)
+        # will not obey instant formatting, because global format_string doesn't allow that;
+        # obeys the global format_string instead
+        actual_result = 'size: {size:.1f}'.format(size=size)
+        self.assertEqual(expected_result, actual_result)
+        bitmath.format_string = orig_fmt_str