Pythonic

這樣寫才 Python

正如寫程式應盡量套用 API，不要老是自己也寫一堆程式碼，把事情變得雜亂。寫 Python 也應該盡量用它特有的表達方式，程式碼看起來才會簡潔，不要把事情變複雜。

例如從其它程式語言過來的人，要交換 a 和 b 變數的資料時，會這樣寫程式：

temp = a a = b b = temp
但在 Python 的話，建議這樣寫：

a, b = b, a
不然一看就知道是從別的語言過來寫 Python 的人，一點也不 Pythonic。

學習寫 Pythonic 的程式碼，就跟懂得套用 API 寫程式是一樣的，並不是什麼高深的技術，而是有沒有善用現成的資源解決問題。所以不要覺得學完 Python 還要學 Pythonic 很討厭，Pythonic 是能把程式寫得更簡單的議題，而不是什麼高深的程式技術，其實去了解 Pythonic 會感到愉快，慶幸自己沒再繼續當冤大頭。

Example 2

# Programming a = ['a', 'aa', 'aaa'] b = a[0] c = a[1] d = a[2] # Pythonic a = ['a', 'aa', 'aaa'] (b, c, d) = a

Example 3

# Programming if a < b and b < c and c < d: pass # Pythonic if a < b < c < d: pass

Example 4

# Programming if a > 0 and a < 10: pass # Pythonic if 0 < a < 10: pass

Example 5

# Programming if f() == True: pass if f() == False: pass # Pythonic if f(): pass if not f(): pass

Example 6

# Programming if len(a) == 0: pass if len(a): pass # Pythonic if not a: pass if a: pass

Example 7

# Programming if a=='a' or a=='aa' or a=='aaa': pass # Pythonic if a in ('a', 'aa', 'aaa'): pass

Example 8

# Programming a = 123 if a: b = 'yes' else: b = 'no' # Pythonic a = 123 b = 'yes' if a else 'no'

Example 9

# Programming a = {'k':'v', 'kk':'vv', 'kkk':'vvv'} b = dict() for key, value in a.items(): b[value] = key # Pythonic a = {'k':'v', 'kk':'vv', 'kkk':'vvv'} b = {value:key for key, value in a.items()}

Example 10

# Programming f = open('file.txt', 'w') try: f.write('') finally: f.close() # Pythonic with open('file.txt', 'w') as f: f.write('')

很 Pythonic 的寫法

還有一些能將複雜程式寫法，用 Python 內建函式加以簡化的範例，會讓你的程式更 Pythonic，讓人覺得你寫 Python 經驗老到。

但不這麼寫就不 Pythonic 嗎？看起來不是，好像是「可以這樣寫 Python 程式」，而不是「務必這樣寫 Python 程式」，因此這些範例另外放～

Example 11

# Programming a = ['a', 'aa', 'aaa'] n = 0 while n < len(a): print(n, a[n]) n += 1 # Pythonic a = ['a','aa','aaa'] for n, x in enumerate(a): print(n, x)

Example 12

# Programming a = 123 if type(a) is type(1): pass # Pythonic a = 123 if isinstance(a, int): pass

Example 13

# Programming a = {'k':'v', 'kk':'vv', 'kkk':'vvv'} b = dict() for key, value in a.items(): b[value] = key # Pythonic a = {'k':'v', 'kk':'vv', 'kkk':'vvv'} a = dict(zip(a.values(), a.keys())) # 比 Example 9 簡單易懂

Example 14

# Programming a = {'aaa':111} b = 0 if 'aaa' in a: b = a['aaa'] else: b = 222 # Pythonic a = {'aaa':111} b = a.get('aaa', 222)

Example 15

# Programming a = ['a', 'aa', 'aaa'] b = '' for n in a: b += n + ':' b = b[:-1] # Pythonic a = ['a', 'aa', 'aaa'] b = ':'.join(a)

Example 16

# Programming a = 'abc' if a[:2] == 'ab': pass # Pythonic a = 'abc' if a.startswith('ab'): pass # 別忘了還有 endswith()

其他建議事項

Example 17

# Programming f = lambda x, y: x + y f(1, 2) # Pythonic def f(x, y): return x + y f(1, 2) # lambda 不是用來產生具名函式，而是用來表現匿名函數。既然要具名，用 def 才對味。

Example 18

# Programming # 沒想過函式傳回多值 # Pythonic def f(): return ('aaa', 'bbb') (a, b) = f()