dramaticlly commented on a change in pull request #4262:
URL: https://github.com/apache/iceberg/pull/4262#discussion_r829721121



##########
File path: python/src/iceberg/expression/literals.py
##########
@@ -0,0 +1,654 @@
+#  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.
+#
+#   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.
+
+import datetime
+import sys
+import uuid
+from decimal import ROUND_HALF_UP, Decimal
+from functools import singledispatch
+from typing import Any
+
+from iceberg.types import PrimitiveType
+
+if sys.version_info >= (3, 8):
+    from functools import singledispatchmethod  # pragma: no cover
+else:
+    from singledispatch import singledispatchmethod  # pragma: no cover
+
+import pytz
+
+from iceberg.types import (
+    BinaryType,
+    BooleanType,
+    DateType,
+    DecimalType,
+    DoubleType,
+    FixedType,
+    FloatType,
+    IntegerType,
+    LongType,
+    Singleton,
+    StringType,
+    TimestampType,
+    TimestamptzType,
+    TimeType,
+    UUIDType,
+)
+
+EPOCH = datetime.datetime.utcfromtimestamp(0)
+
+"""
+Iceberg literal is wrapper class used in expressions, which return unbound 
predicates
+It's being organized as below
+Literal
+|-- AboveMax
+|-- BelowMin
+|-- BaseLiteral
+    |-- StringLiteral
+    |-- FixedLiteral
+    |-- BinaryLiteral
+    |-- ComparableLiteral
+        |-- BooleanLiteral
+        |-- IntegerLiteral
+        |-- LongLiteral
+        |-- FloatLiteral
+        |-- DoubleLiteral
+        |-- DateLiteral
+        |-- TimeLiteral
+        |-- TimestampLiteral
+        |-- DecimalLiteral
+        |-- UUIDLiteral
+"""
+
+
+class Literal:
+    def to(self, type_var: PrimitiveType):
+        raise NotImplementedError()
+
+
+class BaseLiteral(Literal):
+    """Base literal which has a value and can be converted between types"""
+
+    def __init__(self, repr_string: str, value):
+        self._repr_string = repr_string
+        if value is None:
+            raise TypeError("Cannot set value of BaseLiteral to None")
+        self._value = value
+
+    def to(self, type_var):
+        raise NotImplementedError()
+
+    @property
+    def value(self):
+        return self._value
+
+    def __repr__(self):
+        return self._repr_string
+
+    def __str__(self):
+        return str(self._value)
+
+
+@singledispatch
+def literal(value: Any) -> BaseLiteral:
+    """
+    A generic Literal factory to construct an iceberg Literal based on python 
primitive data type
+    using dynamic overloading
+
+    Args:
+        value(python primitive type): the value to be associated with literal
+
+    Example:
+        from iceberg.expressions.literals import literal
+        >>> literal(123)
+        <IntegerLiteral(123)>v
+    """
+    raise TypeError(f"Unimplemented Type Literal for value: {value}")
+
+
[email protected]
+def _(value: bool):
+    return BooleanLiteral(value)
+
+
[email protected]
+def _(value: int):
+    """
+    Upgrade to long if python int is outside the JAVA_MIN_INT and JAVA_MAX_INT
+    """
+    if value < IntegerType.min or value > IntegerType.max:
+        return LongLiteral(value)
+    return IntegerLiteral(value)
+
+
[email protected]
+def _(value: float):
+    """
+    Upgrade to double if python float is outside the JAVA_MIN_FLOAT and 
JAVA_MAX_FLOAT
+    """
+    if value < FloatType.min or value > FloatType.max:
+        return DoubleLiteral(value)
+    return FloatLiteral(value)
+
+
[email protected]
+def _(value: str):
+    return StringLiteral(value)
+
+
[email protected]
+def _(value: uuid.UUID):
+    return UUIDLiteral(value)
+
+
[email protected]
+def _(value: bytes):
+    return FixedLiteral(value)
+
+
[email protected]
+def _(value: bytearray):
+    return BinaryLiteral(value)
+
+
[email protected]
+def _(value: Decimal):
+    return DecimalLiteral(value)
+
+
+class ComparableLiteral(BaseLiteral):
+    def __init__(self, repr_string: str, value):
+        super(ComparableLiteral, self).__init__(repr_string, value)
+
+    def to(self, type_var):
+        raise NotImplementedError()
+
+    def __eq__(self, other):
+        return self.value == other.value
+
+    def __ne__(self, other):
+        return not self.__eq__(other)
+
+    def __lt__(self, other):
+        return self.value < other.value
+
+    def __gt__(self, other):
+        return self.value > other.value
+
+    def __le__(self, other):
+        return self.value <= other.value
+
+    def __ge__(self, other):
+        return self.value >= other.value
+
+
+class AboveMax(Literal, Singleton):
+    def value(self):
+        raise RuntimeError("AboveMax has no value")
+
+    def to(self, type_var):
+        raise RuntimeError("Cannot change the type of AboveMax")
+
+    def __str__(self):
+        return "aboveMax"
+
+
+class BelowMin(Literal, Singleton):
+    def value(self):
+        raise RuntimeError("BelowMin has no value")
+
+    def to(self, type_var):
+        raise RuntimeError("Cannot change the type of BelowMin")
+
+    def __str__(self):
+        return "belowMin"
+
+
+class BooleanLiteral(ComparableLiteral):
+    def __init__(self, value):
+        super(BooleanLiteral, self).__init__(f"BooleanLiteral({value})", value)
+
+    @singledispatchmethod
+    def to(self, type_var):
+        return None
+
+    @to.register(BooleanType)
+    def _(self, type_var):
+        return self
+
+
+class IntegerLiteral(ComparableLiteral):
+    def __init__(self, value):
+        super(IntegerLiteral, self).__init__(f"IntegerLiteral({value})", value)
+
+    @singledispatchmethod
+    def to(self, type_var):
+        return None
+
+    @to.register(IntegerType)
+    def _(self, type_var):
+        return self
+
+    @to.register(LongType)
+    def _(self, type_var):
+        return LongLiteral(self.value)
+
+    @to.register(FloatType)
+    def _(self, type_var):
+        return FloatLiteral(self.value)
+
+    @to.register(DoubleType)
+    def _(self, type_var):
+        return DoubleLiteral(self.value)
+
+    @to.register(DateType)
+    def _(self, type_var):
+        return DateLiteral(self.value)
+
+    @to.register(DecimalType)
+    def _(self, type_var):
+        if type_var.scale == 0:
+            return DecimalLiteral(Decimal(self.value))
+        else:
+            return DecimalLiteral(
+                Decimal(self.value).quantize(
+                    Decimal("." + "".join(["0" for _ in range(1, 
type_var.scale)]) + "1"), rounding=ROUND_HALF_UP

Review comment:
       yeah I was looking into 
[Decimal](https://docs.python.org/3/library/decimal.html#) and looks like the 
quantize is the API supposed to round the Decimal value to its first operant. I 
can kind of see that construct the Decimal from String is for better precision 
compare to float counterpart. 
   
   I am not very familiar with the Decimal and did not find a better API to do 
this, I guess we can keep this as of now and come back if someone find a better 
way to do this ? What do you think

##########
File path: python/tox.ini
##########
@@ -65,6 +69,9 @@ commands =
 [testenv:type-check]
 deps =
     mypy
+    types-pytz

Review comment:
       Thank you for sharing the mypy usage, I removed those 2 and change the 
commands below to 
   `    mypy --no-implicit-optional --install-types --non-interactive --config 
tox.ini src`

##########
File path: python/tox.ini
##########
@@ -25,6 +25,10 @@ deps =
     mock
     pytest
     pyarrow
+    pytz

Review comment:
       Thank you @Fokko , looks like for dependency already exists in 
`setup.cfg`, I did not need to repeat it again in testenv here, removed them as 
suggested

##########
File path: python/src/iceberg/expression/literals.py
##########
@@ -0,0 +1,654 @@
+#  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.
+#
+#   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.
+
+import datetime
+import sys
+import uuid
+from decimal import ROUND_HALF_UP, Decimal
+from functools import singledispatch
+from typing import Any
+
+from iceberg.types import PrimitiveType
+
+if sys.version_info >= (3, 8):
+    from functools import singledispatchmethod  # pragma: no cover
+else:
+    from singledispatch import singledispatchmethod  # pragma: no cover
+
+import pytz
+
+from iceberg.types import (
+    BinaryType,
+    BooleanType,
+    DateType,
+    DecimalType,
+    DoubleType,
+    FixedType,
+    FloatType,
+    IntegerType,
+    LongType,
+    Singleton,
+    StringType,
+    TimestampType,
+    TimestamptzType,
+    TimeType,
+    UUIDType,
+)
+
+EPOCH = datetime.datetime.utcfromtimestamp(0)
+
+"""
+Iceberg literal is wrapper class used in expressions, which return unbound 
predicates
+It's being organized as below
+Literal
+|-- AboveMax
+|-- BelowMin
+|-- BaseLiteral
+    |-- StringLiteral
+    |-- FixedLiteral
+    |-- BinaryLiteral
+    |-- ComparableLiteral

Review comment:
       Yeah I think that's a good point, let me change the parent of 
StringLiteral

##########
File path: python/src/iceberg/expression/literals.py
##########
@@ -0,0 +1,654 @@
+#  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.
+#
+#   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.
+
+import datetime
+import sys
+import uuid
+from decimal import ROUND_HALF_UP, Decimal
+from functools import singledispatch
+from typing import Any
+
+from iceberg.types import PrimitiveType
+
+if sys.version_info >= (3, 8):
+    from functools import singledispatchmethod  # pragma: no cover
+else:
+    from singledispatch import singledispatchmethod  # pragma: no cover
+
+import pytz
+
+from iceberg.types import (
+    BinaryType,
+    BooleanType,
+    DateType,
+    DecimalType,
+    DoubleType,
+    FixedType,
+    FloatType,
+    IntegerType,
+    LongType,
+    Singleton,
+    StringType,
+    TimestampType,
+    TimestamptzType,
+    TimeType,
+    UUIDType,
+)
+
+EPOCH = datetime.datetime.utcfromtimestamp(0)
+
+"""
+Iceberg literal is wrapper class used in expressions, which return unbound 
predicates
+It's being organized as below
+Literal
+|-- AboveMax
+|-- BelowMin
+|-- BaseLiteral
+    |-- StringLiteral
+    |-- FixedLiteral
+    |-- BinaryLiteral
+    |-- ComparableLiteral
+        |-- BooleanLiteral
+        |-- IntegerLiteral
+        |-- LongLiteral
+        |-- FloatLiteral
+        |-- DoubleLiteral
+        |-- DateLiteral
+        |-- TimeLiteral
+        |-- TimestampLiteral
+        |-- DecimalLiteral
+        |-- UUIDLiteral
+"""
+
+
+class Literal:
+    def to(self, type_var: PrimitiveType):
+        raise NotImplementedError()
+
+
+class BaseLiteral(Literal):
+    """Base literal which has a value and can be converted between types"""
+
+    def __init__(self, repr_string: str, value):
+        self._repr_string = repr_string
+        if value is None:
+            raise TypeError("Cannot set value of BaseLiteral to None")
+        self._value = value
+
+    def to(self, type_var):
+        raise NotImplementedError()
+
+    @property
+    def value(self):
+        return self._value
+
+    def __repr__(self):
+        return self._repr_string
+
+    def __str__(self):
+        return str(self._value)
+
+
+@singledispatch
+def literal(value: Any) -> BaseLiteral:
+    """
+    A generic Literal factory to construct an iceberg Literal based on python 
primitive data type
+    using dynamic overloading
+
+    Args:
+        value(python primitive type): the value to be associated with literal
+
+    Example:
+        from iceberg.expressions.literals import literal
+        >>> literal(123)
+        <IntegerLiteral(123)>v
+    """
+    raise TypeError(f"Unimplemented Type Literal for value: {value}")
+
+
[email protected]
+def _(value: bool):
+    return BooleanLiteral(value)
+
+
[email protected]
+def _(value: int):
+    """
+    Upgrade to long if python int is outside the JAVA_MIN_INT and JAVA_MAX_INT
+    """
+    if value < IntegerType.min or value > IntegerType.max:
+        return LongLiteral(value)
+    return IntegerLiteral(value)
+
+
[email protected]
+def _(value: float):
+    """
+    Upgrade to double if python float is outside the JAVA_MIN_FLOAT and 
JAVA_MAX_FLOAT
+    """
+    if value < FloatType.min or value > FloatType.max:
+        return DoubleLiteral(value)
+    return FloatLiteral(value)
+
+
[email protected]
+def _(value: str):
+    return StringLiteral(value)
+
+
[email protected]
+def _(value: uuid.UUID):
+    return UUIDLiteral(value)
+
+
[email protected]
+def _(value: bytes):
+    return FixedLiteral(value)
+
+
[email protected]
+def _(value: bytearray):
+    return BinaryLiteral(value)
+
+
[email protected]
+def _(value: Decimal):
+    return DecimalLiteral(value)
+
+
+class ComparableLiteral(BaseLiteral):
+    def __init__(self, repr_string: str, value):
+        super(ComparableLiteral, self).__init__(repr_string, value)
+
+    def to(self, type_var):
+        raise NotImplementedError()
+
+    def __eq__(self, other):
+        return self.value == other.value
+
+    def __ne__(self, other):
+        return not self.__eq__(other)
+
+    def __lt__(self, other):
+        return self.value < other.value
+
+    def __gt__(self, other):
+        return self.value > other.value
+
+    def __le__(self, other):
+        return self.value <= other.value
+
+    def __ge__(self, other):
+        return self.value >= other.value
+
+
+class AboveMax(Literal, Singleton):
+    def value(self):
+        raise RuntimeError("AboveMax has no value")
+
+    def to(self, type_var):
+        raise RuntimeError("Cannot change the type of AboveMax")
+
+    def __str__(self):
+        return "aboveMax"

Review comment:
       I directly port over the old code, but I also dont see why it have to be 
in lower case, Capitalize as suggested




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