1.7 15个Pythonic的代码示例¶
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，这里小明收集了一些常见的 Pythonic 写法，帮助你养成写优秀代码的习惯。
02. 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)]
03. 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
04. 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)
05. 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
06. 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)
07. 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!'
08. 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']
09. 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)
10. 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
11. 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)
12. 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}
14. 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
15. 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
