先給個數據鏈接：Head First Python 數據集

第五章的問題是幫助Kelly教練獲得每個運動員跑得最快的三個時間

數據集：

• 首先，數據雜亂無章先進行初步處理

按逗號分隔；

把冒號、‘-’都換成‘.’，統一數據格式；

排序

# 時間格式化函數 def sanitize(time_string):if '-' in time_string:splitter = '-'elif ':' in time_string:splitter = ':'else:return(time_string)(mins, secs) = time_string.split(splitter)return(mins + '.' + secs)# 讀取文件內的時間數據 try:with open('james.txt') as jaf:data = jaf.readline()james = data.strip().split(',')with open('julie.txt') as juf:data = juf.readline()julie = data.strip().split(',')with open('mikey.txt') as mif:data = mif.readline()mikey = data.strip().split(',')with open('sarah.txt') as saf:data = saf.readline()sarah = data.strip().split(',') except IOError as err:print("File Error: " + str(err))c_james = [] c_julie = [] c_mikey = [] c_sarah = []# 列表轉換 for each_item in james:c_james.append(sanitize(each_item)) for each_item in julie:c_julie.append(sanitize(each_item)) for each_item in mikey:c_mikey.append(sanitize(each_item)) for each_item in sarah:c_sarah.append(sanitize(each_item)) # 排序輸出 print(sorted(c_james)) print(sorted(c_julie)) print(sorted(c_mikey)) print(sorted(c_sarah))

• 推導列表
• 上面在做列表轉換時，依然有點復雜，代碼重復多，下面我們采用列表推導的方式進行列表轉換

# 時間格式化函數 def sanitize(time_string):if '-' in time_string:splitter = '-'elif ':' in time_string:splitter = ':'else:return(time_string)(mins, secs) = time_string.split(splitter)return(mins + '.' + secs)# 讀取文件內的時間數據 try:with open('james.txt') as jaf:data = jaf.readline()james = data.strip().split(',')with open('julie.txt') as juf:data = juf.readline()julie = data.strip().split(',')with open('mikey.txt') as mif:data = mif.readline()mikey = data.strip().split(',')with open('sarah.txt') as saf:data = saf.readline()sarah = data.strip().split(',') except IOError as err:print("File Error: " + str(err))# 列表轉換 c_james = [sanitize(each_item) for each_item in james] c_julie = [sanitize(each_item) for each_item in julie] c_mikey = [sanitize(each_item) for each_item in mikey] c_sarah = [sanitize(each_item) for each_item in sarah]# 排序輸出 print(sorted(c_james)) print(sorted(c_julie)) print(sorted(c_mikey)) print(sorted(c_sarah))

• 再回到最初的問題上：最快的三個時間（顯然也不能重復）
• 最快的三個時間很簡單，用c_james[0:3]就可以得到，但是，這里存在著重復數據，怎樣去除重復呢？
• 一個辦法是使用迭代的辦法，每當插入數據時，先判斷這個數據在列表中是否已存在，存在則舍棄

# 時間格式化函數 def sanitize(time_string):if '-' in time_string:splitter = '-'elif ':' in time_string:splitter = ':'else:return(time_string)(mins, secs) = time_string.split(splitter)return(mins + '.' + secs)# 讀取文件內的時間數據 try:with open('james.txt') as jaf:data = jaf.readline()james = data.strip().split(',')with open('julie.txt') as juf:data = juf.readline()julie = data.strip().split(',')with open('mikey.txt') as mif:data = mif.readline()mikey = data.strip().split(',')with open('sarah.txt') as saf:data = saf.readline()sarah = data.strip().split(',') except IOError as err:print("File Error: " + str(err))# 列表轉換 james = sorted([sanitize(each_item) for each_item in james]) julie = sorted([sanitize(each_item) for each_item in julie]) mikey = sorted([sanitize(each_item) for each_item in mikey]) sarah = sorted([sanitize(each_item) for each_item in sarah])# 排序輸出 u_james = [] for t in james:if t not in u_james:u_james.append(t) print(u_james[0:3]) u_julie = [] for t in julie:if t not in u_julie:u_julie.append(t) print(u_julie[0:3]) u_mikey = [] for t in mikey:if t not in u_mikey:u_mikey.append(t) print(u_mikey[0:3]) u_sarah = [] for t in sarah:if t not in u_sarah:u_sarah.append(t) print(u_sarah[0:3])

• 此外，Python還給我們提供了集合，集合的特點是無序、無重復
• set() 創建一個空集合

# 時間格式化函數 def sanitize(time_string):if '-' in time_string:splitter = '-'elif ':' in time_string:splitter = ':'else:return(time_string)(mins, secs) = time_string.split(splitter)return(mins + '.' + secs)# 讀取文件內的時間數據 try:with open('james.txt') as jaf:data = jaf.readline()james = data.strip().split(',')with open('julie.txt') as juf:data = juf.readline()julie = data.strip().split(',')with open('mikey.txt') as mif:data = mif.readline()mikey = data.strip().split(',')with open('sarah.txt') as saf:data = saf.readline()sarah = data.strip().split(',') except IOError as err:print("File Error: " + str(err))# 列表轉換、排序、輸出 james = sorted(set([sanitize(each_item) for each_item in james]))[0:3] print(james) julie = sorted(set([sanitize(each_item) for each_item in julie]))[0:3] print(julie) mikey = sorted(set([sanitize(each_item) for each_item in mikey]))[0:3] print(mikey) sarah = sorted(set([sanitize(each_item) for each_item in sarah]))[0:3] print(sarah)

• 文件讀取部分依然有許多重復，封裝文件讀取部分

# 時間格式化函數 def sanitize(time_string):if '-' in time_string:splitter = '-'elif ':' in time_string:splitter = ':'else:return(time_string)(mins, secs) = time_string.split(splitter)return(mins + '.' + secs)# 對文件讀取進行封裝 def reader(file):try:with open(file) as datafile:return (datafile.readline().strip().split(','))except IOError as err:print("File Error: " + str(err))return (None) # 讀取文件內的時間數據 james = reader('james.txt') julie = reader('julie.txt') mikey = reader('mikey.txt') sarah = reader('sarah.txt')# 列表轉換、排序、輸出 james = sorted(set([sanitize(each_item) for each_item in james]))[0:3] print(james) julie = sorted(set([sanitize(each_item) for each_item in julie]))[0:3] print(julie) mikey = sorted(set([sanitize(each_item) for each_item in mikey]))[0:3] print(mikey) sarah = sorted(set([sanitize(each_item) for each_item in sarah]))[0:3] print(sarah)

• BULLET　POINTS
• 排序的兩種方法，list.sort()"原地"排序，sorted(list)“復制”排序，幾乎可以對任何數據結構排序。
• 向sort()或sotred()傳入reverse=True可以按降序排序。
• 如果有一下代碼

new_l = [] for t in old_l:new_l.append(len(t))

使用列表推導重寫這個代碼，可以寫作：

new_l = [len(t) for t in old_l]

• 要訪問列表中多個數據，可以使用分片。例如：my_list[0:3]，這會訪問0，1，2三個位置的數據。

• 使用set()工廠方法可以創建一個集合。

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