03 - 串列¶
- 序列型別
- 可變與不可變
- 序列共同介面
- 序列的應用
- 附錄-進階練習
In [1]:
my_list1 = ["a",2016,5566,"PyLadies"]
my_list2 = []
my_list3 = my_list1+[2016,2016.0]
my_list4 = [1,2,3]*3
print (my_list1,bool(my_list1))
print (my_list2,bool(my_list2))
print (my_list3)
print (my_list4)
In [2]:
# 索引值 0 , 1 , 2 , 3 , 4 , 5
my_list = ["a",2016,5566,"PyLadies",2016,2016.0] # 這是一個長度為6的串列
print ("The 4th element",my_list[3])
print ("The last element",my_list[-1]) # 等同於拿取索引=6-1=5的元素
print ("The second-last element",my_list[-2]) # 等同於拿取索引=6-2=4的元素
In [3]:
my_list = ["a",2016,5566,"PyLadies",2016,2016.0]
b = my_list[1]
my_list[2] = 2017
print(b)
print(my_list)
「字串」跟「串列」很像¶
- 字串的每個元素都是一個字元(字母或符號)
- 用同樣的方式存取元素
In [4]:
my_string = "PyLadies Taiwan"
print ("The 1st element of my_string = ",my_string[0])
print ("The 8th element of my_string = ",my_string[7])
print ("The last element of my_string = ",my_string[-1])
!注意¶
- 索引不能超過界線
In [5]:
print(my_string[20])
[練習]¶
這裡有一群按照身高排序的人，可以告訴我最高和最矮差了幾公分嗎？
(請不要直接 print(192-145)，試試看剛才學的串列取值)
people = [145,148,151,153,158,161,163,164,166,168,170,172,175,192]
Hint:¶
- 因為身高是有排序過的，最矮是第一個元素，最高是最後一個
=> 最後一個減第一個
判斷是否指向同一個物件¶
s is t、s is not t
In [6]:
a = 3
b = 3
c = a
print(a is b,a is c)
print(id(a),id(b),id(c))
a += 2 # a = 5
b = 4
print(a is b,a is c)
print(id(a),id(b),id(c))
不可變物件，進行運算、或是重新指向，都是直接指向新的物件。
In [7]:
l1 = ["a",2016,5566,"PyLadies"]
l2 = l1
print(l1 is l2,id(l1),id(l2))
In [8]:
l1 += ["Hi"]
print(l1 is l2,id(l1),id(l2))
print(l1)
print(l2)
In [9]:
l2[2] = 2017
print(l1 is l2,id(l1),id(l2))
print(l1)
print(l2)
!注意¶
- 可變物件不管怎麼修改，位置還是不會變的
- 如果有兩個名稱指向同一個可變物件，物件一修改，
兩個名稱取到的都會是同樣一個修改之後的物件
序列共同介面¶
前面提到的利用 序列[索引] 存取元素，也是共同介面之一！
In [10]:
my_string = "PyLadies Taiwan"
my_list = ["a",2016,5566,"PyLadies",2016,2016.0]
print ("Length of my_string = ",len(my_string))
print ("Length of my_list = ",len(my_list))
數值計算¶
max(串列)：序列中最大值min(串列)：序列中最小值sum(串列)：序列總和，針對全數字序列才有用
In [11]:
l = [3, 4, 2.1, 1]
s = "PyLadies"
print(max(l),min(l),sum(l))
print(max(s),min(s))
print(sum(s))
[練習]¶
統計全班的成績狀況：
- 全班最高分與最低分的落差為？ (Ans. 58)
- 全班分數的平均為？ (Ans. 71.4285...)
score_of_each_student = [85,70,54,87,98,66,40]
Hint:¶
- 平均：學生分數總和/學生總數
- 總數：序列長度
- 最高分：序列最大值
- 最低分：序列最小值
In [13]:
my_string = "PyLadies Taiwan"
if "PyLadies" in my_string:
print ("\"PyLadies\" found")
if "Python" in my_string:
print ("\"Python\" found")
if "Taiwan" in my_string:
print ("\"Taiwan\" found")
In [14]:
my_list = ["a",2016,5566,"PyLadies",2016,2016.0]
print(2016 in my_list)
print("2016" in my_list)
In [15]:
my_string = "PyLadies Taiwan"
my_list = ["a",2016,5566,"PyLadies",2016,2016.0]
print ("The time 'a' appears in my_string = ",my_string.count('a'))
print ("The time '2016' appears in my_string = ",my_list.count(2016))
想想看¶
要用什麼序列方法，找出以下這篇文章，出現幾次「in」
In [16]:
article = """
Bubble tea represents the "QQ" food texture that Taiwanese love.
The phrase refers to something that is especially chewy, like the tapioca balls that form the 'bubbles' in bubble tea.
It's said this unusual drink was invented out of boredom.
"""
print (article.count("in"))
「in」的確在文章出現4次：someth"in"g、"in"、dr"in"k、"in"vented
但如果我們想要的是代表單字的「in」，就需要把文章分割，再來計算！
序列的應用¶
In [17]:
s = "Hi PyLadies Taiwan"
l = s.split(" ")
print (l)
print (s.split(" ",1))
print (s)
print (l[0])
print (l[-1])
In [18]:
article = """
Bubble tea represents the "QQ" food texture that Taiwanese love.
The phrase refers to something that is especially chewy, like the tapioca balls that form the 'bubbles' in bubble tea.
It's said this unusual drink was invented out of boredom.
"""
那這篇文章出現幾次「tea」呢？
In [20]:
article = """
Bubble tea represents the "QQ" food texture that Taiwanese love.
The phrase refers to something that is especially chewy, like the tapioca balls that form the 'bubbles' in bubble tea.
It's said this unusual drink was invented out of boredom.
"""
可是文章中我們有看到兩次的tea，怎麼只算一次?
原因是因為split之後，是分成「tea」、「tea.」
這兩個是不同的字串，以count("tea")來說，就只會算到剛好等於「tea」的字
所以可以先將常用標點符號取代之後再來計算！
同樣道理，
如果是用要用in判斷，找「單字」是否存在字串中，
記得先分割成單字的字串才使用
In [23]:
my_string = "PyLadies Taiwan"
if "Py" in my_string:
print ("\"Py\" found in my_string")
my_string_list = my_string.split(" ")
if "Py" in my_string_list:
print ("\"Py\" found in my_string_list")
應用情境 - 日期正規化 (年-月-日 時:分:秒)¶
In [24]:
ebc_datetime = "2016-10-17 17:00"
back_datetime = "2016-10-11, 19:55"
ptt_datatime = "Tue Oct 18 23:22:05 2016"
format_ebc_datetime = ebc_datetime+":00"
format_back_datetime = back_datetime.replace(",","")+":00"
# ptt
ptt_split_list = ptt_datatime.split(" ")
ptt_year = ptt_split_list[-1]
ptt_month = ptt_split_list[1].replace("Oct","10")
ptt_date = ptt_split_list[2]
ptt_time = ptt_split_list[3]
format_ptt_datetime = "{}-{}-{} {}".format(ptt_year,ptt_month,ptt_date,ptt_time)
print (format_ebc_datetime)
print (format_back_datetime)
print (format_ptt_datetime)
應用情境 - 日期正規化 (年-月-日 時:分:秒) 24小時制¶
In [25]:
yahoo_datetime = "2016年10月18日 下午10:33"
temp_yahoo_date = yahoo_datetime.split(" ")[0].replace("年","-").replace("月","-")
temp_yahoo_date = temp_yahoo_date.replace("日","")
temp_yahoo_time = yahoo_datetime.split(" ")[-1]
temp_yahoo_hour = temp_yahoo_time.split(":")[0]
temp_yahoo_mins = temp_yahoo_time.split(":")[-1]
if "下午" in temp_yahoo_hour:
temp_yahoo_hour_int = int(temp_yahoo_hour.replace("下午",""))+12
temp_yahoo_hour = str(temp_yahoo_hour_int)
else:
temp_yahoo_hour_int = int(temp_yahoo_hour.replace("上午",""))
temp_yahoo_hour = str(temp_yahoo_hour_int)
format_yahoo_datetime = "{} {}:{}:00".format(temp_yahoo_date,temp_yahoo_hour,temp_yahoo_mins)
print (format_yahoo_datetime)
In [26]:
l = ["Hello","PyLadies","Taiwan"]
s = "Hi PyLadies"
print (" ".join(l))
print (".".join(s))
應用情境 - 正規化 ('人名1','人名2','人名3')¶
- 常用在SQL語法
In [27]:
l = ["Kelly","Mars","Maomao"]
s = "','".join(l)
print(s)
print("('{}')".format(s))
想想看¶
如果我要算這篇文章，每個單字出現幾次：
In [28]:
article = """Bubble tea represents the "QQ" food texture that Taiwanese love.
The phrase refers to something that is especially chewy, like the tapioca balls that form the 'bubbles' in bubble tea.
It's said this unusual drink was invented out of boredom.
"""
word_of_article = article.split(" ")
print(word_of_article[0],word_of_article.count(word_of_article[0]))
print(word_of_article[1],word_of_article.count(word_of_article[1]))
print(word_of_article[2],word_of_article.count(word_of_article[2]))
總不能一個個慢慢寫吧...
下一章節就會教到程式語言中很厲害的技巧：「迴圈」，
在任何程式語言中「串列」+「迴圈」基本上可以解決大部分的問題！
Hint:¶
keyin = input("請輸入您要計算的內容，限二個數字 ex: 2**3\n")
if "+" in keyin:
"以+號分割字串，從串列中分別取得兩個數字並貼上標籤，印出兩數相加"
elif "-" in keyin:
"以-號分割字串，從串列中分別取得兩個數字並貼上標籤，印出兩數相減"
.
.
.