add function to parse canonical quantities (e.g. resources)

This utility function is useful to parse values like the 200m or 300Gi
memory and cpu resources stored in kubernetes manifests.
It uses Decimal as output format as it usually represents typical input
values more accurately and reduces rounding errors.

kubernetes/test/test_quantity.py

@@ -0,0 +1,112 @@
+# coding: utf-8
+# Copyright 2019 The Kubernetes Authors.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+from __future__ import absolute_import
+
+import unittest
+from kubernetes.utils import parse_quantity
+from decimal import Decimal
+
+
+class TestQuantity(unittest.TestCase):
+    def test_parse(self):
+        self.assertIsInstance(parse_quantity(2.2), Decimal)
+        # input, expected output
+        tests = [
+            (0, 0),
+            (2, 2),
+            (2, Decimal("2")),
+            (2., 2),
+            (Decimal("2.2"), Decimal("2.2")),
+            (2., Decimal(2)),
+            (Decimal("2."), 2),
+            ("123", 123),
+            ("2", 2),
+            ("2n", Decimal("2") * Decimal(1000)**-3),
+            ("2u", Decimal("0.000002")),
+            ("2m", Decimal("0.002")),
+            ("0m", Decimal("0")),
+            ("0M", Decimal("0")),
+            ("223k", 223000),
+            ("002M", 2 * 1000**2),
+            ("2M", 2 * 1000**2),
+            ("4123G", 4123 * 1000**3),
+            ("2T", 2 * 1000**4),
+            ("2P", 2 * 1000**5),
+            ("2E", 2 * 1000**6),
+
+            ("223Ki", 223 * 1024),
+            ("002Mi", 2 * 1024**2),
+            ("2Mi", 2 * 1024**2),
+            ("2Gi", 2 * 1024**3),
+            ("4123Gi", 4123 * 1024**3),
+            ("2Ti", 2 * 1024**4),
+            ("2Pi", 2 * 1024**5),
+            ("2Ei", 2 * 1024**6),
+
+            ("2.34n", Decimal("2.34") * Decimal(1000)**-3),
+            ("2.34u", Decimal("2.34") * Decimal(1000)**-2),
+            ("2.34m", Decimal("2.34") * Decimal(1000)**-1),
+            ("2.34Ki", Decimal("2.34") * 1024),
+            ("2.34", Decimal("2.34")),
+            (".34", Decimal("0.34")),
+            ("34.", 34),
+            (".34M", Decimal("0.34") * 1000**2),
+
+            ("2e2K", Decimal("2e2") * 1000),
+            ("2e2Ki", Decimal("2e2") * 1024),
+            ("2e-2Ki", Decimal("2e-2") * 1024),
+            ("2.34E1", Decimal("2.34E1")),
+            (".34e-2", Decimal("0.34e-2")),
+        ]
+
+        for inp, out in tests:
+            self.assertEqual(parse_quantity(inp), out)
+            if isinstance(inp, (int, float, Decimal)):
+                self.assertEqual(parse_quantity(-1 * inp), -out)
+            else:
+                self.assertEqual(parse_quantity("-" + inp), -out)
+                self.assertEqual(parse_quantity("+" + inp), out)
+
+    def test_parse_invalid(self):
+        self.assertRaises(ValueError, parse_quantity, [])
+        self.assertRaises(ValueError, parse_quantity, "")
+        self.assertRaises(ValueError, parse_quantity, "-")
+        self.assertRaises(ValueError, parse_quantity, "i")
+        self.assertRaises(ValueError, parse_quantity, "2i")
+        self.assertRaises(ValueError, parse_quantity, "2mm")
+        self.assertRaises(ValueError, parse_quantity, "2mmKi")
+        self.assertRaises(ValueError, parse_quantity, "2KKi")
+        self.assertRaises(ValueError, parse_quantity, "2e")
+        self.assertRaises(ValueError, parse_quantity, "2.2i")
+        self.assertRaises(ValueError, parse_quantity, "bla")
+        self.assertRaises(ValueError, parse_quantity, "Ki")
+        self.assertRaises(ValueError, parse_quantity, "M")
+        self.assertRaises(ValueError, parse_quantity, "2ki")
+        self.assertRaises(ValueError, parse_quantity, "2Ki ")
+        self.assertRaises(ValueError, parse_quantity, "20Ki ")
+        self.assertRaises(ValueError, parse_quantity, "20B")
+        self.assertRaises(ValueError, parse_quantity, "20Bi")
+        self.assertRaises(ValueError, parse_quantity, "20.2Bi")
+        self.assertRaises(ValueError, parse_quantity, "2MiKi")
+        self.assertRaises(ValueError, parse_quantity, "2MK")
+        self.assertRaises(ValueError, parse_quantity, "2MKi")
+        self.assertRaises(ValueError, parse_quantity, "234df")
+        self.assertRaises(ValueError, parse_quantity, "df234")
+        self.assertRaises(ValueError, parse_quantity, tuple())
+
+
+if __name__ == '__main__':
+    unittest.main()

kubernetes/utils/__init__.py

@@ -16,3 +16,4 @@
 
 from .create_from_yaml import (FailToCreateError, create_from_dict,
                                create_from_yaml)
+from .quantity import parse_quantity

kubernetes/utils/quantity.py

@@ -0,0 +1,75 @@
+# Copyright 2019 The Kubernetes Authors.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+from decimal import Decimal, InvalidOperation
+
+
+def parse_quantity(quantity):
+    """
+    Parse kubernetes canonical form quantity like 200Mi to a decimal number.
+    Supported SI suffixes:
+    base1024: Ki | Mi | Gi | Ti | Pi | Ei
+    base1000: n | u | m | "" | k | M | G | T | P | E
+
+    See https://github.com/kubernetes/apimachinery/blob/master/pkg/api/resource/quantity.go
+
+    Input:
+    quanity: string. kubernetes canonical form quantity
+
+    Returns:
+    Decimal
+
+    Raises:
+    ValueError on invalid or unknown input
+    """
+    if isinstance(quantity, (int, float, Decimal)):
+        return Decimal(quantity)
+
+    exponents = {"n": -3, "u": -2, "m": -1, "K": 1, "k": 1, "M": 2,
+                 "G": 3, "T": 4, "P": 5, "E": 6}
+
+    quantity = str(quantity)
+    number = quantity
+    suffix = None
+    if len(quantity) >= 2 and quantity[-1] == "i":
+        if quantity[-2] in exponents:
+            number = quantity[:-2]
+            suffix = quantity[-2:]
+    elif len(quantity) >= 1 and quantity[-1] in exponents:
+        number = quantity[:-1]
+        suffix = quantity[-1:]
+
+    try:
+        number = Decimal(number)
+    except InvalidOperation:
+        raise ValueError("Invalid number format: {}".format(number))
+
+    if suffix is None:
+        return number
+
+    if suffix.endswith("i"):
+        base = 1024
+    elif len(suffix) == 1:
+        base = 1000
+    else:
+        raise ValueError("{} has unknown suffix".format(quantity))
+
+    # handly SI inconsistency
+    if suffix == "ki":
+        raise ValueError("{} has unknown suffix".format(quantity))
+
+    if suffix[0] not in exponents:
+        raise ValueError("{} has unknown suffix".format(quantity))
+
+    exponent = Decimal(exponents[suffix[0]])
+    return number * (base ** exponent)