03_迴圈 - HackMD

--- tags: python --- # 03_迴圈 ## for 迴圈 * 宣告迴圈種類(for) * 宣告一個疊代子 iterator (可自由命名) * 宣告一個迴圈要跑的sequence (list, dict...) ```python weekdays = ["Monday", "Tuesday", "Wednesday", "Thursday", "Friday"] for wk in weekdays: # 一次印出一天 print(wk) # Monday # Tuesday # Wednesday # Thursday # Friday # 從1數到5 # range()函數第一個參數為開始索引值(不填寫則預設為0) # range()函數第二個參數為結束索引值，但不包含結束索引值本身 for n in range(1, 6): # 需要數到5，因此第二參數填入5 + 1 print(n) # 1 # 2 # 3 # 4 # 5 ``` ### 印出九九乘法表 ```python for i in range(1, 10): for j in range(1, 10): print(f'{i} x {j} = {i * j}') ''' 1 x 1 = 1 1 x 2 = 2 1 x 3 = 3 ...中間略... 9 x 7 = 63 9 x 8 = 72 9 x 9 = 81 ''' ``` ### 用for迴圈做出sum()函數背後的邏輯 ```python nums = [2, 4, 5, 8, 10] print(sum(nums)) # 29 # 預設一個變數為0 summation = 0 # 將串列資料依次取出加進去 for num in nums: summation += num # 迴圈結束後印出結果 print(summation) # 29 ``` ### 用for迴圈遍歷一個字典 ```python dog = {'age': 3, 'breed': 'beagle', 'size': 'medium'} # 如果sequence是一個字典，迴圈只會印出Key for info in dog: print(info) # age # breed # beagle # 取得字典內的值，方法一 for info in dog: print(dog[info]) # 取得字典內的值，方法二 for value in dog.values(): print(value) # 3 # beagle # medium # 同時取得字典內的Key: Value for info, value in dog.items(): print(info, value) # age 3 # breed beagle # size medium ``` ### 收支計算 ```python ''' 透過迴圈計算餘額(balance)欄位計算每月紀錄所有income, expense, balance的加總 ''' records = [ {"income": 40000, "expense": 23000}, {"income": 60000, "expense": 54000}, {"income": 22000, "expense": 35000}, {"income": 32000, "expense": 40000}, {"income": 70000, "expense": 20000} ] # 預設income及expense加總為0 total_income = 0 total_expense = 0 for record in records: record['balance'] = record['income'] - record['expense'] total_income += record['income'] total_expense += record['expense'] print(records) # 印出加上balance欄位後的收支紀錄 print(total_income) # 224000 print(total_expense) # 172000 ``` ### 最常與for迴圈併用的函數enumerate() ```python bus_list = [ {'name': '643', 'arrive_time': 1}, {'name': '648', 'arrive_time': 3}, {'name': '綠1', 'arrive_time': 15}, {'name':'644','arrive_time': 30} ] # i為索引值，bus為迭代子 for i, bus in bus_list: name = bus['name'] time = bus['arrive_time'] report = f'第{i}班即將進站公車為{name}，將於{time}分鐘後抵達' print(report) # 第1班即將進站公車為643，將於1分鐘後抵達 # 第2班即將進站公車為648，將於3分鐘後抵達 # 第3班即將進站公車為綠1，將於15分鐘後抵達 # 第4班即將進站公車為644，將於30分鐘後抵達 ``` ### 用zip()函數一次跑多個sequence ```python name_list = ['seq1', 'seq2', 'seq3'] seq_list = ['ATTA', 'CGTA', 'ATCG'] for name, seq in zip(name_list, seq_list): seq_set = { 'name': name, 'seq': seq } seq_collection.append(seq_set) print(seq_collection) # [{'name': 'seq1', 'seq': 'ATTA'}, {'name': 'seq2', 'seq': 'CGTA'}, {'name': 'seq3', 'seq': 'ATCG'}] ``` ### 串列生成式使用生成式generator快速產生需求串列 ```python # 生成1到100的偶數串列 # 當n可以被2整除餘數為0時，即為偶數 even_nums = [n for n in range(1, 101) if n % 2 == 0] print(even_nums) # [2, 4, 6, 8, 10, 12, 14, 16, 18, 20, 22, 24, 26, 28, 30, 32, 34, 36, 38, 40, 42, 44, 46, 48, 50, 52, 54, 56, 58, 60, 62, 64, 66, 68, 70, 72, 74, 76, 78, 80, 82, 84, 86, 88, 90, 92, 94, 96, 98, 100] ``` ## while迴圈 * 不確定會執行幾次的迴圈就必須使用while迴圈 * 所有for迴圈都可以用while迴圈改寫，反之則不一定 ### while迴圈的結構 ```python while 某個判斷條件為`True`時: # 執行甚麼事 ``` ### 從0開始累加，+1+2+3..到多少時會超過1000 ```python # 預設總和為0 summation = 0 # 開始要加的數字為1 n = 1 # 紀錄每個被加過的數字 records = [] # 當總和還是<=1000，就讓迴圈繼續跑 while summation <= 1000: summation += n records.append(n) n += 1 print(records[-1]) # 最後一個被加的數字為45 print(summation) # 1035 ``` ### Fibonacci數列 ```python ''' fn = fn-1 + fn-2 試著取得第20個fibonacci數字是多少 ''' f1 = 1 f2 = 1 fibonacci = [f1, f2] # 當資料數量為20時，即<20為`False`，迴圈結束 while len(fibonacci) < 20: fib = fibonacci[-1] + fibonacci[-2] fibonacci.append(fib) print(fibonacci[-1]) # 6765 ``` > Written with [StackEdit](https://stackedit.io/).