feat: make Column and Row iterable (#55)

Closes #47.

### Summary of Changes

* Add `__iter__` method to `Column` and `Row` to iterate over the
values:
  * Iterating over a `Column` returns the values.
* Iterating over a `Row` returns the column names, as specified in the
[documenetation of
`__iter__`](https://docs.python.org/3/reference/datamodel.html#object.__iter__).
* Add `__len__` method to `Column` and `Row` to compute their length.
* Change superclasses of exceptions as needed for
[`__getitem__`](https://docs.python.org/3/reference/datamodel.html#object.__getitem__):
  * Change superclass of `IndexOutOfBoundsError` to `IndexError`.
  * Change superclass of `UnknownColumnNameError` to `KeyError`.

---------

Co-authored-by: lars-reimann <[email protected]>

Author: lars-reimann

src/safeds/data/tabular/_column.py

@@ -2,7 +2,7 @@
 
 import typing
 from numbers import Number
-from typing import Any, Callable
+from typing import Any, Callable, Iterator
 
 import numpy as np
 import pandas as pd
@@ -34,6 +34,10 @@ def name(self) -> str:
         """
         return self._name
 
+    @property
+    def statistics(self) -> ColumnStatistics:
+        return ColumnStatistics(self)
+
     @property
     def type(self) -> ColumnType:
         """
@@ -46,9 +50,35 @@ def type(self) -> ColumnType:
         """
         return self._type
 
+    def __eq__(self, other: object) -> bool:
+        if not isinstance(other, Column):
+            return NotImplemented
+        if self is other:
+            return True
+        return self._data.equals(other._data) and self.name == other.name
+
     def __getitem__(self, index: int) -> Any:
         return self.get_value(index)
 
+    def __hash__(self) -> int:
+        return hash(self._data)
+
+    def __iter__(self) -> Iterator[Any]:
+        return iter(self._data)
+
+    def __len__(self) -> int:
+        return len(self._data)
+
+    def __repr__(self) -> str:
+        tmp = self._data.to_frame()
+        tmp.columns = [self.name]
+        return tmp.__repr__()
+
+    def __str__(self) -> str:
+        tmp = self._data.to_frame()
+        tmp.columns = [self.name]
+        return tmp.__str__()
+
     def get_value(self, index: int) -> Any:
         """
         Return column value at specified index, starting at 0.
@@ -73,10 +103,6 @@ def get_value(self, index: int) -> Any:
 
         return self._data[index]
 
-    @property
-    def statistics(self) -> ColumnStatistics:
-        return ColumnStatistics(self)
-
     def count(self) -> int:
         """
         Return the number of elements in the column.
@@ -223,26 +249,6 @@ def get_unique_values(self) -> list[typing.Any]:
         """
         return list(self._data.unique())
 
-    def __eq__(self, other: object) -> bool:
-        if not isinstance(other, Column):
-            return NotImplemented
-        if self is other:
-            return True
-        return self._data.equals(other._data) and self.name == other.name
-
-    def __hash__(self) -> int:
-        return hash(self._data)
-
-    def __str__(self) -> str:
-        tmp = self._data.to_frame()
-        tmp.columns = [self.name]
-        return tmp.__str__()
-
-    def __repr__(self) -> str:
-        tmp = self._data.to_frame()
-        tmp.columns = [self.name]
-        return tmp.__repr__()
-
     def _ipython_display_(self) -> DisplayHandle:
         """
         Return a display object for the column to be used in Jupyter Notebooks.
@@ -378,7 +384,6 @@ def sum(self) -> float:
         return self._column._data.sum()
 
     def variance(self) -> float:
-
         """
         Return the variance of the column. The column has to be numerical.
 
@@ -401,7 +406,6 @@ def variance(self) -> float:
         return self._column._data.var()
 
     def standard_deviation(self) -> float:
-
         """
         Return the standard deviation of the column. The column has to be numerical.
 

src/safeds/data/tabular/_row.py

@@ -16,6 +16,12 @@ def __init__(self, data: typing.Iterable, schema: TableSchema):
     def __getitem__(self, column_name: str) -> Any:
         return self.get_value(column_name)
 
+    def __iter__(self) -> typing.Iterator[Any]:
+        return iter(self.get_column_names())
+
+    def __len__(self) -> int:
+        return len(self._data)
+
     def get_value(self, column_name: str) -> Any:
         """
         Return the value of a specified column.
@@ -34,6 +40,17 @@ def get_value(self, column_name: str) -> Any:
             raise UnknownColumnNameError([column_name])
         return self._data[self.schema._get_column_index_by_name(column_name)]
 
+    def count(self) -> int:
+        """
+        Return the number of columns in this row.
+
+        Returns
+        -------
+        count : int
+            The number of columns.
+        """
+        return len(self._data)
+
     def has_column(self, column_name: str) -> bool:
         """
         Return whether the row contains a given column.

src/safeds/exceptions/_data_exceptions.py

@@ -1,4 +1,4 @@
-class UnknownColumnNameError(Exception):
+class UnknownColumnNameError(KeyError):
     """
     Exception raised for trying to access an invalid column name.
 
@@ -37,7 +37,7 @@ def __init__(self, column_name: str):
         super().__init__(f"Column '{column_name}' already exists.")
 
 
-class IndexOutOfBoundsError(Exception):
+class IndexOutOfBoundsError(IndexError):
     """
     Exception raised for trying to access an element by an index that does not exist in the underlying data.
 

tests/safeds/data/tabular/_column/test_column.py

@@ -9,7 +9,7 @@ def test_from_columns() -> None:
     assert column1._type == column2._type
 
 
-def negative_test_from_columns() -> None:
+def test_from_columns_negative() -> None:
     column1 = Column(pd.Series([1, 4]), "A")
     column2 = Column(pd.Series(["2", "5"]), "B")
 

tests/safeds/data/tabular/_column/test_count.py

@@ -1,7 +1,6 @@
-import pandas as pd
-from safeds.data.tabular import Table
+from safeds.data.tabular import Column
 
 
 def test_count_valid() -> None:
-    table = Table(pd.DataFrame(data={"col1": [1, 2, 3, 4, 5], "col2": [2, 3, 4, 5, 6]}))
-    assert table.get_column("col1").count() == 5
+    column = Column([1, 2, 3, 4, 5], "col1")
+    assert column.count() == 5

tests/safeds/data/tabular/_column/test_iter.py

@@ -0,0 +1,6 @@
+from safeds.data.tabular import Column
+
+
+def test_iter() -> None:
+    column = Column([0, "1"], "testColumn")
+    assert list(column) == [0, "1"]

tests/safeds/data/tabular/_column/test_len.py

@@ -0,0 +1,6 @@
+from safeds.data.tabular import Column
+
+
+def test_count_valid() -> None:
+    column = Column([1, 2, 3, 4, 5], "col1")
+    assert len(column) == 5

tests/safeds/data/tabular/_row/test_count.py

@@ -0,0 +1,12 @@
+from safeds.data.tabular import Row
+from safeds.data.tabular.typing import IntColumnType, StringColumnType, TableSchema
+
+
+def test_count() -> None:
+    row = Row(
+        [0, "1"],
+        TableSchema(
+            {"testColumn1": IntColumnType(), "testColumn2": StringColumnType()}
+        ),
+    )
+    assert row.count() == 2

tests/safeds/data/tabular/_row/test_iter.py

@@ -0,0 +1,12 @@
+from safeds.data.tabular import Row
+from safeds.data.tabular.typing import IntColumnType, StringColumnType, TableSchema
+
+
+def test_iter() -> None:
+    row = Row(
+        [0, "1"],
+        TableSchema(
+            {"testColumn1": IntColumnType(), "testColumn2": StringColumnType()}
+        ),
+    )
+    assert list(row) == ["testColumn1", "testColumn2"]

tests/safeds/data/tabular/_row/test_len.py

@@ -0,0 +1,12 @@
+from safeds.data.tabular import Row
+from safeds.data.tabular.typing import IntColumnType, StringColumnType, TableSchema
+
+
+def test_count() -> None:
+    row = Row(
+        [0, "1"],
+        TableSchema(
+            {"testColumn1": IntColumnType(), "testColumn2": StringColumnType()}
+        ),
+    )
+    assert len(row) == 2