Merge branch 'feature/control-flow' into develop

jsonbender/__init__.py

@@ -2,6 +2,7 @@
 from jsonbender.list_ops import FlatForall, Forall, Filter, Reduce
 from jsonbender.string_ops import Format
 from jsonbender.selectors import F, K, S, OptionalS
+from jsonbender.control_flow import Alternation, If, Switch
 
 
 __version__ = '0.8.1'

jsonbender/control_flow.py

@@ -0,0 +1,109 @@
+from jsonbender.core import Bender
+from jsonbender.selectors import K
+
+
+class If(Bender):
+    """
+    Takes a condition bender, and two benders (both default to K(None)).
+    If the condition bender evaluates to true, return the value of the first
+    bender. If it evaluates to false, return the value of the second bender.
+
+    Example:
+    ```
+    if_ = If(S('country') == K('China'), S('first_name'), S('last_name'))
+    if_({'country': 'China',
+         'first_name': 'Li',
+         'last_name': 'Na'})  # ->  'Li'
+
+    if_({'country': 'Brazil',
+         'first_name': 'Gustavo',
+         'last_name': 'Kuerten'})  # -> 'Kuerten'
+
+    ```
+    """
+
+    def __init__(self, condition, when_true=K(None), when_false=K(None)):
+        self.condition = condition
+        self.when_true = when_true
+        self.when_false = when_false
+
+    def execute(self, val):
+        return (self.when_true(val)
+                if self.condition(val)
+                else self.when_false(val))
+
+
+class Alternation(Bender):
+    """
+    Take any number of benders, and return the value of the first one that
+    doesn't raise a LookupError (KeyError, IndexError etc.).
+    If all benders raise LookupError, re-raise the last raised exception.
+
+    Example:
+    ```
+    b = Alternation(S(1), S(0), S('key1'))
+    b(['a', 'b'])  #  -> 'b'
+    b(['a'])  #  -> 'a'
+    b([])  #  -> KeyError
+    b({})  #  -> KeyError
+    b({'key1': 23})  # -> 23
+    ```
+    """
+
+    def __init__(self, *benders):
+        self.benders = benders
+
+    def execute(self, source):
+        exc = ValueError()
+        for bender in self.benders:
+            try:
+                result = bender(source)
+            except LookupError as e:
+                exc = e
+            else:
+                return result
+        else:
+            raise exc
+
+
+class Switch(Bender):
+    """
+    Take a key bender, a 'case' container of benders and a default bender
+    (optional).
+    The value returned by the key bender is used to get a bender from the
+    case container, which then returns the result.
+    If the key is not in the case container, the default is used.
+    If it's unavailable, raise the original LookupError.
+
+    Example:
+    ```
+    b = Switch(S('service'),
+               {'twitter': S('handle'),
+                'mastodon': S('handle') + K('@') + S('server')},
+               default=S('email'))
+
+    b({'service': 'twitter', 'handle': 'etandel'})  #  -> 'etandel'
+    b({'service': 'mastodon', 'handle': 'etandel',
+       'server': 'mastodon.social'})  #  -> '[email protected]'
+    b({'service': 'facebook',
+       'email': '[email protected]'})  #  -> '[email protected]'
+    ```
+    """
+
+    def __init__(self, key_bender, cases, default=None):
+        self.key_bender = key_bender
+        self.cases = cases
+        self.default = default
+
+    def execute(self, source):
+        key = self.key_bender(source)
+        try:
+            bender = self.cases[key]
+        except LookupError:
+            if self.default:
+                bender = self.default
+            else:
+                raise
+
+        return bender(source)
+

tests/test_control_flow.py

@@ -0,0 +1,82 @@
+from operator import add
+import unittest
+
+from jsonbender import Context, K, S, bend
+from jsonbender.control_flow import If, Alternation, Switch
+from jsonbender.test import BenderTestMixin
+
+
+class TestIf(BenderTestMixin, unittest.TestCase):
+    def setUp(self):
+        self.na_li = {'country': 'China',
+                      'first_name': 'Li',
+                      'last_name': 'Na'}
+        self.guga = {'country': 'Brazil',
+                     'first_name': 'Gustavo',
+                     'last_name': 'Kuerten'}
+
+    def test_if_true(self):
+        if_ = If(S('country') == K('China'), S('first_name'), S('last_name'))
+        self.assert_bender(if_, self.na_li, 'Li')
+
+    def test_if_false(self):
+        if_ = If(S('country') == K('China'), S('first_name'), S('last_name'))
+        self.assert_bender(if_, self.guga, 'Kuerten')
+
+    def test_if_true_default(self):
+        if_ = If(S('country') == K('China'), when_false=S('last_name'))
+        self.assert_bender(if_, self.na_li, None)
+
+    def test_if_false_default(self):
+        if_ = If(S('country') == K('China'), S('first_name'))
+        self.assert_bender(if_, self.guga, None)
+
+
+class TestAlternation(BenderTestMixin, unittest.TestCase):
+    def test_empty_benders(self):
+        self.assertRaises(ValueError, Alternation(), {})
+
+    def test_matches(self):
+        bender = Alternation(S(1), S(0), S('key1'))
+        self.assert_bender(bender, ['a', 'b'], 'b')
+        self.assert_bender(bender, ['a'], 'a')
+        self.assert_bender(bender, {'key1': 23}, 23)
+
+    def test_no_match(self):
+        self.assertRaises(IndexError, Alternation(S(1)), [])
+        self.assertRaises(KeyError, Alternation(S(1)), {})
+
+
+class TestSwitch(BenderTestMixin, unittest.TestCase):
+    def test_match(self):
+        bender = Switch(S('service'),
+                        {'twitter': S('handle'),
+                         'mastodon': S('handle') + K('@') + S('server')},
+                        default=S('email'))
+
+        self.assert_bender(bender,
+                           {'service': 'twitter', 'handle': 'etandel'},
+                           'etandel')
+        self.assert_bender(bender,
+                           {'service': 'mastodon',
+                            'handle': 'etandel',
+                            'server': 'mastodon.social'},
+                           '[email protected]')
+
+    def test__no_match_with_default(self):
+        bender = Switch(S('service'),
+                        {'twitter': S('handle'),
+                         'mastodon': S('handle') + K('@') + S('server')},
+                        default=S('email'))
+        self.assert_bender(bender,
+                           {'service': 'facebook',
+                            'email': '[email protected]'},
+                           '[email protected]')
+
+    def test__no_match_without_default(self):
+        self.assertRaises(KeyError, Switch(S('key'), {}), {'key': None})
+
+
+if __name__ == '__main__':
+    unittest.main()
+