Merge pull request #239 from realpython/hashtable

Materials supplementing the hash table tutorial

Author: iansedano

hashtable/01_hashtable_prototype/01_define_a_custom_hashtable_class/hashtable.py

@@ -0,0 +1,9 @@
+# hashtable.py
+
+
+class HashTable:
+    def __init__(self, capacity):
+        self.values = capacity * [None]
+
+    def __len__(self):
+        return len(self.values)

hashtable/01_hashtable_prototype/01_define_a_custom_hashtable_class/test_hashtable.py

@@ -0,0 +1,15 @@
+# test_hashtable.py
+
+from hashtable import HashTable
+
+
+def test_should_create_hashtable():
+    assert HashTable(capacity=100) is not None
+
+
+def test_should_report_capacity():
+    assert len(HashTable(capacity=100)) == 100
+
+
+def test_should_create_empty_value_slots():
+    assert HashTable(capacity=3).values == [None, None, None]

hashtable/01_hashtable_prototype/02_insert_a_key_value_pair/hashtable.py

@@ -0,0 +1,15 @@
+# hashtable.py
+
+BLANK = object()
+
+
+class HashTable:
+    def __init__(self, capacity):
+        self.values = capacity * [BLANK]
+
+    def __len__(self):
+        return len(self.values)
+
+    def __setitem__(self, key, value):
+        index = hash(key) % len(self)
+        self.values[index] = value

hashtable/01_hashtable_prototype/02_insert_a_key_value_pair/test_hashtable.py

@@ -0,0 +1,39 @@
+# test_hashtable.py
+
+from hashtable import HashTable, BLANK
+
+
+def test_should_create_hashtable():
+    assert HashTable(capacity=100) is not None
+
+
+def test_should_report_capacity():
+    assert len(HashTable(capacity=100)) == 100
+
+
+def test_should_create_empty_value_slots():
+    assert HashTable(capacity=3).values == [BLANK, BLANK, BLANK]
+
+
+def test_should_insert_key_value_pairs():
+    hash_table = HashTable(capacity=100)
+
+    hash_table["hola"] = "hello"
+    hash_table[98.6] = 37
+    hash_table[False] = True
+
+    assert "hello" in hash_table.values
+    assert 37 in hash_table.values
+    assert True in hash_table.values
+
+    assert len(hash_table) == 100
+
+
+def test_should_not_contain_none_value_when_created():
+    assert None not in HashTable(capacity=100).values
+
+
+def test_should_insert_none_value():
+    hash_table = HashTable(capacity=100)
+    hash_table["key"] = None
+    assert None in hash_table.values

hashtable/01_hashtable_prototype/03_find_a_value_by_key/hashtable.py

@@ -0,0 +1,36 @@
+# hashtable.py
+
+BLANK = object()
+
+
+class HashTable:
+    def __init__(self, capacity):
+        self.values = capacity * [BLANK]
+
+    def __len__(self):
+        return len(self.values)
+
+    def __setitem__(self, key, value):
+        index = hash(key) % len(self)
+        self.values[index] = value
+
+    def __getitem__(self, key):
+        index = hash(key) % len(self)
+        value = self.values[index]
+        if value is BLANK:
+            raise KeyError(key)
+        return value
+
+    def __contains__(self, key):
+        try:
+            self[key]
+        except KeyError:
+            return False
+        else:
+            return True
+
+    def get(self, key, default=None):
+        try:
+            return self[key]
+        except KeyError:
+            return default

hashtable/01_hashtable_prototype/03_find_a_value_by_key/test_hashtable.py

@@ -0,0 +1,87 @@
+# test_hashtable.py
+
+import pytest
+
+from hashtable import HashTable, BLANK
+
+
+@pytest.fixture
+def hash_table():
+    sample_data = HashTable(capacity=100)
+    sample_data["hola"] = "hello"
+    sample_data[98.6] = 37
+    sample_data[False] = True
+    return sample_data
+
+
+def test_should_create_hashtable():
+    assert HashTable(capacity=100) is not None
+
+
+def test_should_report_capacity():
+    assert len(HashTable(capacity=100)) == 100
+
+
+def test_should_create_empty_value_slots():
+    assert HashTable(capacity=3).values == [BLANK, BLANK, BLANK]
+
+
+def test_should_insert_key_value_pairs():
+    hash_table = HashTable(capacity=100)
+
+    hash_table["hola"] = "hello"
+    hash_table[98.6] = 37
+    hash_table[False] = True
+
+    assert "hello" in hash_table.values
+    assert 37 in hash_table.values
+    assert True in hash_table.values
+
+    assert len(hash_table) == 100
+
+
+def test_should_not_contain_none_value_when_created():
+    assert None not in HashTable(capacity=100).values
+
+
+def test_should_insert_none_value():
+    hash_table = HashTable(capacity=100)
+    hash_table["key"] = None
+    assert None in hash_table.values
+
+
+def test_should_find_value_by_key(hash_table):
+    assert hash_table["hola"] == "hello"
+    assert hash_table[98.6] == 37
+    assert hash_table[False] is True
+
+
+def test_should_raise_error_on_missing_key():
+    hash_table = HashTable(capacity=100)
+    with pytest.raises(KeyError) as exception_info:
+        hash_table["missing_key"]
+    assert exception_info.value.args[0] == "missing_key"
+
+
+def test_should_find_key(hash_table):
+    assert "hola" in hash_table
+
+
+def test_should_not_find_key(hash_table):
+    assert "missing_key" not in hash_table
+
+
+def test_should_get_value(hash_table):
+    assert hash_table.get("hola") == "hello"
+
+
+def test_should_get_none_when_missing_key(hash_table):
+    assert hash_table.get("missing_key") is None
+
+
+def test_should_get_default_value_when_missing_key(hash_table):
+    assert hash_table.get("missing_key", "default") == "default"
+
+
+def test_should_get_value_with_default(hash_table):
+    assert hash_table.get("hola", "default") == "hello"

hashtable/01_hashtable_prototype/04_delete_a_key_value_pair/hashtable.py

@@ -0,0 +1,43 @@
+# hashtable.py
+
+BLANK = object()
+
+
+class HashTable:
+    def __init__(self, capacity):
+        self.values = capacity * [BLANK]
+
+    def __len__(self):
+        return len(self.values)
+
+    def __delitem__(self, key):
+        if key in self:
+            self[key] = BLANK
+        else:
+            raise KeyError(key)
+
+    def __setitem__(self, key, value):
+        self.values[self._index(key)] = value
+
+    def __getitem__(self, key):
+        value = self.values[self._index(key)]
+        if value is BLANK:
+            raise KeyError(key)
+        return value
+
+    def __contains__(self, key):
+        try:
+            self[key]
+        except KeyError:
+            return False
+        else:
+            return True
+
+    def get(self, key, default=None):
+        try:
+            return self[key]
+        except KeyError:
+            return default
+
+    def _index(self, key):
+        return hash(key) % len(self)

hashtable/01_hashtable_prototype/04_delete_a_key_value_pair/test_hashtable.py

@@ -0,0 +1,105 @@
+# test_hashtable.py
+
+import pytest
+
+from hashtable import HashTable, BLANK
+
+
+@pytest.fixture
+def hash_table():
+    sample_data = HashTable(capacity=100)
+    sample_data["hola"] = "hello"
+    sample_data[98.6] = 37
+    sample_data[False] = True
+    return sample_data
+
+
+def test_should_create_hashtable():
+    assert HashTable(capacity=100) is not None
+
+
+def test_should_report_capacity():
+    assert len(HashTable(capacity=100)) == 100
+
+
+def test_should_create_empty_value_slots():
+    assert HashTable(capacity=3).values == [BLANK, BLANK, BLANK]
+
+
+def test_should_insert_key_value_pairs():
+    hash_table = HashTable(capacity=100)
+
+    hash_table["hola"] = "hello"
+    hash_table[98.6] = 37
+    hash_table[False] = True
+
+    assert "hello" in hash_table.values
+    assert 37 in hash_table.values
+    assert True in hash_table.values
+
+    assert len(hash_table) == 100
+
+
+def test_should_not_contain_none_value_when_created():
+    assert None not in HashTable(capacity=100).values
+
+
+def test_should_insert_none_value():
+    hash_table = HashTable(capacity=100)
+    hash_table["key"] = None
+    assert None in hash_table.values
+
+
+def test_should_find_value_by_key(hash_table):
+    assert hash_table["hola"] == "hello"
+    assert hash_table[98.6] == 37
+    assert hash_table[False] is True
+
+
+def test_should_raise_error_on_missing_key():
+    hash_table = HashTable(capacity=100)
+    with pytest.raises(KeyError) as exception_info:
+        hash_table["missing_key"]
+    assert exception_info.value.args[0] == "missing_key"
+
+
+def test_should_find_key(hash_table):
+    assert "hola" in hash_table
+
+
+def test_should_not_find_key(hash_table):
+    assert "missing_key" not in hash_table
+
+
+def test_should_get_value(hash_table):
+    assert hash_table.get("hola") == "hello"
+
+
+def test_should_get_none_when_missing_key(hash_table):
+    assert hash_table.get("missing_key") is None
+
+
+def test_should_get_default_value_when_missing_key(hash_table):
+    assert hash_table.get("missing_key", "default") == "default"
+
+
+def test_should_get_value_with_default(hash_table):
+    assert hash_table.get("hola", "default") == "hello"
+
+
+def test_should_delete_key_value_pair(hash_table):
+    assert "hola" in hash_table
+    assert "hello" in hash_table.values
+    assert len(hash_table) == 100
+
+    del hash_table["hola"]
+
+    assert "hola" not in hash_table
+    assert "hello" not in hash_table.values
+    assert len(hash_table) == 100
+
+
+def test_should_raise_key_error_when_deleting(hash_table):
+    with pytest.raises(KeyError) as exception_info:
+        del hash_table["missing_key"]
+    assert exception_info.value.args[0] == "missing_key"