[GR-24387] Fix: filter should return lazy iterable.

PullRequest: graalpython/1067

Author: steve-s

graalpython/com.oracle.graal.python.test/src/tests/test_filter.py

@@ -0,0 +1,67 @@
+# Copyright (c) 2020, 2020, Oracle and/or its affiliates. All rights reserved.
+# DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
+#
+# The Universal Permissive License (UPL), Version 1.0
+#
+# Subject to the condition set forth below, permission is hereby granted to any
+# person obtaining a copy of this software, associated documentation and/or
+# data (collectively the "Software"), free of charge and under any and all
+# copyright rights in the Software, and any and all patent rights owned or
+# freely licensable by each licensor hereunder covering either (i) the
+# unmodified Software as contributed to or provided by such licensor, or (ii)
+# the Larger Works (as defined below), to deal in both
+#
+# (a) the Software, and
+#
+# (b) any piece of software and/or hardware listed in the lrgrwrks.txt file if
+# one is included with the Software each a "Larger Work" to which the Software
+# is contributed by such licensors),
+#
+# without restriction, including without limitation the rights to copy, create
+# derivative works of, display, perform, and distribute the Software and make,
+# use, sell, offer for sale, import, export, have made, and have sold the
+# Software and the Larger Work(s), and to sublicense the foregoing rights on
+# either these or other terms.
+#
+# This license is subject to the following condition:
+#
+# The above copyright notice and either this complete permission notice or at a
+# minimum a reference to the UPL must be included in all copies or substantial
+# portions of the Software.
+#
+# THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+# IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+# FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+# AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+# LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+# OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+# SOFTWARE.
+
+
+def assert_iterable_eq(iterable, list):
+    list_idx = 0
+    for item in iterable:
+        assert list_idx < len(list), "iterable is too long"
+        assert item == list[list_idx], "difference at index " + str(list_idx) + ", got: " + repr(item)
+        list_idx += 1
+    assert list_idx == len(list), "iterator does not have enough items"
+
+
+def test_filter():
+    assert_iterable_eq(filter(lambda a: a >= 3 and a < 5, [1,2,3,4,5]), [3,4])
+    assert_iterable_eq(filter(lambda a: True, [1,2,3]), [1,2,3])
+    assert_iterable_eq(filter(lambda a: False, [1,2,3]), [])
+    it = filter(lambda a: False, [1,2,3])
+    assert next(it, None) is None
+
+
+def test_filter_side_effect():
+    shared = 0
+    def fun(x):
+        nonlocal shared
+        shared = 42
+        return True
+    it = filter(fun, [1,2,3])
+    assert shared == 0
+    assert next(it) == 1
+    assert shared == 42

graalpython/com.oracle.graal.python.test/src/tests/unittest_tags/test_builtin.txt

@@ -9,6 +9,7 @@
 *graalpython.lib-python.3.test.test_builtin.BuiltinTest.test_delattr
 *graalpython.lib-python.3.test.test_builtin.BuiltinTest.test_exec
 *graalpython.lib-python.3.test.test_builtin.BuiltinTest.test_exec_redirected
+*graalpython.lib-python.3.test.test_builtin.BuiltinTest.test_filter
 *graalpython.lib-python.3.test.test_builtin.BuiltinTest.test_hex
 *graalpython.lib-python.3.test.test_builtin.BuiltinTest.test_id
 *graalpython.lib-python.3.test.test_builtin.BuiltinTest.test_isinstance

graalpython/lib-graalpython/functions.py

@@ -59,16 +59,6 @@ def all(iterable):
     return True
 
 
-@__graalpython__.builtin
-def filter(func, iterable):
-    result = []
-    predicate = func if func is not None else lambda a: a
-    for i in iterable:
-        if predicate(i):
-            result.append(i)
-    return tuple(result)
-
-
 # This is re-defined later during bootstrap in classes.py
 def __build_class__(func, name, *bases, metaclass=None, **kwargs):
     """
@@ -137,3 +127,22 @@ def input(prompt=None):
         else:
             break
     return "".join(result)
+
+
+class filter(object):
+    def __init__(self, predicateOrNone, iterable):
+        self.predicateOrNone = predicateOrNone
+        self.iterable = iter(iterable)
+
+    def __iter__(self):
+        return self
+
+    def __next__(self):
+        while True:
+            item = next(self.iterable)
+            if self.predicateOrNone is None:
+                if item:
+                    return item
+            else:
+                if self.predicateOrNone(item):
+                    return item