Pythonic【15个代码示例】
Python由于语言的简洁性,让我们以人类思考的方式来写代码,新手更容易上手,老鸟更爱不释手。
要写出 Pythonic(优雅的、地道的、整洁的)代码,还要平时多观察那些大牛代码,Github 上有很多非常优秀的源代码值得阅读,比如:requests、flask、tornado,这里收集了一些常见的 Pythonic 写法,帮助你养成写优秀代码的习惯。
变量交换
- Bad
tmp = a a = b b = tmp
- Pythonic
a,b = b,a
列表推导
- Bad
my_list = [] for i in range(10): my_list.append(i*2)
- Pythonic
my_list = [i*2 for i in range(10)]
单行表达式
- 虽然列表推导式由于其简洁性及表达性,被广受推崇。
- 但是有许多可以写成单行的表达式,并不是好的做法。
- Bad
print 'one'; print 'two' if x == 1: print 'one' if <complex comparison> and <other complex comparison>: # do something
- Pythonic
print 'one' print 'two' if x == 1: print 'one' cond1 = <complex comparison> cond2 = <other complex comparison> if cond1 and cond2: # do something
带索引遍历
- Bad
for i in range(len(my_list)): print(i, "-->", my_list[i])
- Pythonic
for i,item in enumerate(my_list): print(i, "-->",item)
序列解包
- Pythonic
a, *rest = [1, 2, 3] # a = 1, rest = [2, 3] a, *middle, c = [1, 2, 3, 4] # a = 1, middle = [2, 3], c = 4 1
字符串拼接
- Bad
letters = ['s', 'p', 'a', 'm'] s="" for let in letters: s += let
- Pythonic
letters = ['s', 'p', 'a', 'm'] word = ''.join(letters)
真假判断
- Bad
if attr == True: print 'True!' if attr == None: print 'attr is None!'
- Pythonic
if attr: print 'attr is truthy!' if not attr: print 'attr is falsey!' if attr is None: print 'attr is None!'
访问字典元素
- Bad
d = {'hello': 'world'} if d.has_key('hello'): print d['hello'] # prints 'world' else: print 'default_value'
- Pythonic
d = {'hello': 'world'} print d.get('hello', 'default_value') # prints 'world' print d.get('thingy', 'default_value') # prints 'default_value' # Or: if 'hello' in d: print d['hello']
操作列表
- Bad
a = [3, 4, 5] b = [] for i in a: if i > 4: b.append(i)
- Pythonic
a = [3, 4, 5] b = [i for i in a if i > 4] # Or: b = filter(lambda x: x > 4, a)
- Bad
a = [3, 4, 5] for i in range(len(a)): a[i] += 3
- Pythonic
a = [3, 4, 5] a = [i + 3 for i in a] # Or: a = map(lambda i: i + 3, a)
文件读取
- Bad
f = open('file.txt') a = f.read() print a f.close()
- Pythonic
with open('file.txt') as f: for line in f: print line
代码续行
- Bad
my_very_big_string = """For a long time I used to go to bed early. Sometimes, \ when I had put out my candle, my eyes would close so quickly that I had not even \ time to say “I’m going to sleep.”""" from some.deep.module.inside.a.module import a_nice_function, another_nice_function, \ yet_another_nice_function
- Pythonic
my_very_big_string = ( "For a long time I used to go to bed early. Sometimes, " "when I had put out my candle, my eyes would close so quickly " "that I had not even time to say “I’m going to sleep.”" ) from some.deep.module.inside.a.module import ( a_nice_function, another_nice_function, yet_another_nice_function)
显式代码
- Bad
def make_complex(*args): x, y = args return dict(**locals())
- Pythonic
def make_complex(x, y): return {'x': x, 'y': y}
使用占位符
- Pythonic
filename = 'foobar.txt' basename, _, ext = filename.rpartition('.')
链式比较
- Bad
if age > 18 and age < 60: print("young man")
- Pythonic
if 18 < age < 60: print("young man")
- 理解了链式比较操作,那么你应该知道为什么下面这行代码输出的结果是 False
>>> False == False == True
False
三目运算
这个保留意见。随使用习惯就好。
- Bad
if a > 2: b = 2 else: b = 1 #b = 2
- Pythonic
a = 3 b = 2 if a > 2 else 1 #b = 2
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===============Talk is cheap, show me the code,bye-bye================