defaultdict data structure. (huangsam#105)

j3r3mias · huangsam · web-flow · commit c5ae8bb05caa · 2023-10-19T03:44:34.000-07:00
* defaultdict data structure.

* E201.

* Using an EPS value to compare floats.

* E302.

* READMEs.

---------

Co-authored-by: Samuel Huang &lt;samhuang91@gmail.com&gt;
diff --git a/README.de.md b/README.de.md
@@ -92,6 +92,7 @@ Es gibt zwei Möglichkeiten, die Module auszuführen:
     - String: [String operations](ultimatepython/data_structures/string.py) (:cake:)
     - Deque: [deque](ultimatepython/data_structures/deque.py) (:exploding_head:)
     - Namedtuple: [namedtuple](ultimatepython/data_structures/namedtuple.py) (:exploding_head:)
+    - Defaultdict: [defaultdict](ultimatepython/data_structures/defaultdict.py) (:exploding_head:)
     - Time complexity: [cPython operations](https://wiki.python.org/moin/TimeComplexity) (:books:, :exploding_head:)
 4. **Klassen**
     - Basic class: [Basic definition](ultimatepython/classes/basic_class.py) (:cake:)
diff --git a/README.es.md b/README.es.md
@@ -91,6 +91,7 @@ Hay dos maneras de ejecutar los módulos:
     - Cadena: [Operaciones con strings](ultimatepython/data_structures/string.py) (:cake:)
     - Deque: [deque](ultimatepython/data_structures/deque.py) (:exploding_head:)
     - Namedtuple: [namedtuple](ultimatepython/data_structures/namedtuple.py) (:exploding_head:)
+    - Defaultdict: [defaultdict](ultimatepython/data_structures/defaultdict.py) (:exploding_head:)
     - Complejidad de tiempo: [Operaciones de cPython](https://wiki.python.org/moin/TimeComplexity) (:books:, :exploding_head:)
 4. **Clases**
     - Clase básica: [Definición de básica](ultimatepython/classes/basic_class.py) (:cake:)
diff --git a/README.ko.md b/README.ko.md
@@ -80,6 +80,7 @@ Repl.it와 같은 브라우저에서 실행할 수있는 독립형 모듈 모음
     - 문자열 : [문자열 연산](ultimatepython/data_structures/string.py) (:cake:)
     - Deque: [deque](ultimatepython/data_structures/deque.py) (:exploding_head:)
     - Namedtuple: [namedtuple](ultimatepython/data_structures/namedtuple.py) (:exploding_head:)
+    - Defaultdict: [defaultdict](ultimatepython/data_structures/defaultdict.py) (:exploding_head:)
     - 시간 복잡성 : [cPython 작업](https://wiki.python.org/moin/TimeComplexity) (:books:, :exploding_head:)
 4. **클래스**
     - 기본 클래스 : [기본 정의](ultimatepython/classes/basic_class.py) (:cake:)
diff --git a/README.md b/README.md
@@ -93,6 +93,7 @@ There are two ways of running the modules:
     - String: [String operations](ultimatepython/data_structures/string.py) (:cake:)
     - Deque: [deque](ultimatepython/data_structures/deque.py) (:exploding_head:)
     - Namedtuple: [namedtuple](ultimatepython/data_structures/namedtuple.py) (:exploding_head:)
+    - Defaultdict: [defaultdict](ultimatepython/data_structures/defaultdict.py) (:exploding_head:)
     - Time complexity: [cPython operations](https://wiki.python.org/moin/TimeComplexity) (:books:, :exploding_head:)
 4. **Classes**
     - Basic class: [Basic definition](ultimatepython/classes/basic_class.py) (:cake:)
diff --git a/README.zh_tw.md b/README.zh_tw.md
@@ -76,6 +76,7 @@ print("Ultimate Python 學習大綱")
     - 字串：[字串操作](ultimatepython/data_structures/string.py) (:cake:)
     - 雙端隊列：[deque](ultimatepython/data_structures/deque.py) (:exploding_head:)
     - Namedtuple: [namedtuple](ultimatepython/data_structures/namedtuple.py) (:exploding_head:)
+    - Defaultdict: [defaultdict](ultimatepython/data_structures/defaultdict.py) (:exploding_head:)
     - 時間複雜度：[cPython操作](https://wiki.python.org/moin/TimeComplexity) (:books:, :exploding_head:)
 4. **類別**
     - 基本類別：[基本定義](ultimatepython/classes/basic_class.py) (:cake:)
diff --git a/ultimatepython/data_structures/defaultdict.py b/ultimatepython/data_structures/defaultdict.py
@@ -0,0 +1,57 @@
+"""
+This module demonstrates the use of defaultdict, which is a dictionary that is
+possible to setup a default value in its creation.
+"""
+
+from collections import defaultdict
+
+# Module-level constants
+_GPA_MIN = 0.0
+_GPA_MAX = 4.0
+_EPS = 0.000001
+
+
+def main():
+    # Let's create a defaultdict with student keys and GPA values. The first
+    # parameter is called default_factory and it is the initialization value for
+    # first use of a key. It can be a common type or a function
+    student_gpa = defaultdict(float, [("john", 3.5), ("bob", 2.8), ("mary", 3.2)])
+
+    # There are three student records in this dictionary
+    assert len(student_gpa) == 3
+
+    # Each student has a name key and a GPA value
+    assert len(student_gpa.keys()) == len(student_gpa.values())
+
+    # We can get the names in isolation. Note that in Python 3.7 and
+    # above, dictionary entries are sorted in the order that they were
+    # defined or inserted
+    student_names = []
+    for student in student_gpa.keys():
+        student_names.append(student)
+    assert student_names == ["john", "bob", "mary"]
+
+    # We can get the GPA for a specific student
+    assert abs(student_gpa["john"] < 3.5) < _EPS
+
+    # And the defaultdict allow us to get the GPA of a student that is not in
+    # the data structure yet, returning a default value for float that is 0.0
+    assert student_gpa["jane"] == _GPA_MIN
+
+    # And now there are four student records in this dictionary
+    assert len(student_gpa) == 4
+
+    # You can set the default value in default_factory attribute
+    def set_default_to_gpa_max():
+        return _GPA_MAX
+
+    student_gpa.default_factory = set_default_to_gpa_max
+
+    assert student_gpa["rika"] == _GPA_MAX
+
+    # And now there are five student records in this dictionary
+    assert len(student_gpa) == 5
+
+
+if __name__ == "__main__":
+    main()
