What is Dict

用其他的方式來宣告

ex_dict = dict([["bday", 928], ["name", "Kain"]]) #傳入一個List/Tuple 
# 每個元素為一個鍵值對 可用List/Tuple

What is Dict

Dictionary 字典
用大括號來宣告
最大的特色是可以用數字之外的物件來取值

ex_dict = {"bday": 928} #這裡以字串為例
ex_list = [928]
print(ex_list["bday"], ex_list[0])

Key-Value Pairs 鍵值對

What is Dict

mon_list = ["Jan", "Feb", "Mar", ..., "Sep"]
mon_dict = {"一月": "Jan", "二月": "Feb", "三月": "Mar", "九月": "Sep"}
print(mon_list[0], mon_dict["一月"])

What is Dict

萬一資料不是有順序的呢？

location_dict = {"台北": "Taipei", "桃園": "Taoyuan"}

What is Dict

ex_dict = {"Mutated": "變異的", "Crab": "螃蟹"}
print(ex_dict["Mutated"]) #一個長得很像字典的範例 
print(ex_dict["變異的"]) # 不能反向！
print(ex_dict["Dior"]) # 不能找沒在字典裡面的

最後兩行會導致Key Error
都是因為字典內沒有對應Key導致

Practice

用三種方式宣告一個字典

keys_list = ["名字", "屬性", "顏色"]
value_list = ["皮卡丘", "雷系", "顏色"]

Practice

用三種方式宣告一個字典

keys_list = ["名字", "屬性", "顏色"]
value_list = ["皮卡丘", "雷系", "顏色"]
# Hints:
# 用大括號
# 用dict()及雙層list
# (bonus) 

How do Dict works

Dict 是用一個酷東西"Hash"來實作的

這裡是參考資料 不會講

How do Dict works

Hashable:
String, Tuple, Numbers, Frozen Set, Lambda Function(?)

好玩的參考資料

Usage

新增

info = {}
info["Kain"] = 928
print(info["Kain"])

Usage

修改

info = {"Kain": 928}
info["Kain"] = "B09"
print(info["Kain"])

Usage

刪除

info = {"Kain":928}
info.pop("Kain")
print("Kain" in info)

Usage

刪除

info = {"Kain": 928}
del info["Kain"]
print("Kain" in info) # 確認 "Kain"-928 還在不在

Usage

全部刪除！

info = {"Kain":928, ""}
info.clear() 

Usage

迭代

calories = {"apple":243, "banana":132, "candy":432}
for i in calories:
    print(i) 

for會迭代Key:Value裡面的Key

Usage

迭代(Key)

calories = {"apple":243, "banana":132, "candy":432}
for i in calories.keys():
    print(i) 

Usage

迭代(Value)

calories = {"apple":243, "banana":132, "candy":432}
for i in calories.values():
    print(i) 

Usage

迭代(Key,Value)

calories = {"apple":243, "banana":132, "candy":432}
for i in calories.items():
    print(i) 

會將 (Key,Value) 組合成Tuple來迭代

Usage

合併兩個字典

dict_a = {"學校": "CKHS", "年級": "10th"}
dict_b = {"類組": "三", "校排": "10%"}
dict_c = merge(dict_a,dict_b)??? #這是psudo-code 不要記

Usage

合併兩個字典
用update
用星號爆開

dict_c = {**dict_a, **dict_b} # c為合併後的字典
dict_a.update(dict_b) # a為合併後的字典
#暴雷：之後可以用星號 *list_a / **dict_a 炸開並傳入func當作參數

Combo Skills

What is Key Error

student = {}
student["Kain"] = "B09"
print(student["Jolin"])

Combo Skills

先檢查再取值

if "Jolin" in student:
    print(student["Jolin"])

Combo Skills

也可以用Method

print(student.get("Jolin")) 

Quiz

1. 給定任意Dict 請輸出一個Key-Value對調的dict (要比下面的更好)
2. 給出一個Dict 把下面的版本弄壞

ans_dict = dict()
for k,v in given_dict.item():
    ans_dict[v] = k

Set

• unordered
• hashable elements only
• mutable
  • frozenset for immutable usage
• NO duplicated elements

Set

dict_a = {}
set_a = set(["Vokda","Rum","Gin","Orange Juice"])
set_a.add("Tequila")
set_a.remove("Orange Juice")

Set

src : learnbyexample

Set

Union

set_a = {1, 2, 3, 5, 8, 13}
set_b = {2, 3, 5, 7, 11, 13}
print(set_a.union(set_b))
print(set_a | set_b) # Elegant!

Set

Intersection

set_a = {1, 2, 3, 5, 8, 13}
set_b = {2, 3, 5, 7, 11, 13}
print(set_a.intersection(set_b))
print(set_a & set_b) # Elegant!

Set

Difference

set_a = {1, 2, 3, 5, 8, 13}
set_b = {2, 3, 5, 7, 11, 13}
print(set_a.difference(set_b))
print(set_a-set_b) # Elegant!

Set

Symmetric Difference

set_a = {1, 2, 3, 5, 8, 13}
set_b = {2, 3, 5, 7, 11, 13}
print(set_a.symmetric_difference(set_b))
print(set_a^set_b) # Elegant!

Set

src: Spy X Family

Function

f(x) = 9 x + 28
f(100) = 928
f(3) = ?
f(?) = 73

定義妥善的f需要有

• 定義域/值域
• 好的演算法

e.g. \(\sin(x), \tan(x)\)

Hash Function

好的Hash Function需要有

• hard to reverse
• easy to compute
• \(x=y \leftrightarrow h(x) = h(y)\)
• Given \(h(x)\), hard to find \(x\)

e.g. SHA256 SHA512

Hash Function

• 保護密碼
• 將定義域的東西壓進值域
• 誰是臥底（？）

Hash Function

f(x) = x%17
g(x) = 2x + 3

Hash Fucntion

f(x) = x裡字母a的數量