Python中那些 Pythonic的写法详解

age = 18
if age > 18 and age < 60:
print("young man")

if 18 < age < 60:
print("young man")

> False == False == True 
False

if gender == 'male':
text = '男'
else:
text = '女'

text = '男' if gender == 'male' else '女'

if attr == True:
do_something()
if len(values) != 0: # 判断列表是否为空
do_something()

if attr:
do_something()
if values:
do_something()

flagfound = False
for i in mylist:
if i == theflag:
flagfound = True
break
process(i)
if not flagfound:
raise ValueError("List argument missing terminal flag.")

for i in mylist:
if i == theflag:
break
process(i)
else:
raise ValueError("List argument missing terminal flag.")

s1 = "foofish.net"
s2 = "vttalk"
s3 = "welcome to %s and following %s" % (s1, s2)

s3 = "welcome to {blog} and following {wechat}".format(blog="foofish.net", wechat="vttalk")

items = range(10)
# 奇数
odd_items = []
for i in items:
if i % 2 != 0:
odd_items.append(i)
# 拷贝
copy_items = []
for i in items:
copy_items.append(i)

# 第1到第4个元素的范围区间
sub_items = items[1:4]
# 奇数
odd_items = items[1::2]
#拷贝
copy_items = items[::] 或者 items[:]

--------------------------
| P | y | t | h | o | n |
--------------------------
 0 1 2 3 4 5 
 -6 -5 -4 -3 -2 -1
--------------------------

def fib(n):
a, b = 0, 1
result = []
while b < n:
result.append(b)
a, b = b, a+b
return result

def fib(n):
a, b = 0, 1
while a < n:
yield a
a, b = b, a + b

d = {'name': 'foo'}
if d.has_key('name'):
print(d['name'])
else:
print('unkonw')

d.get("name", "unknow")

data = [('foo', 10), ('bar', 20), ('foo', 39), ('bar', 49)]
groups = {}
for (key, value) in data:
if key in groups:
groups[key].append(value)
else:
groups[key] = [value]

#　第一种方式
groups = {}
for (key, value) in data:
groups.setdefault(key, []).append(value)

# 第二种方式
from collections import defaultdict
groups = defaultdict(list)
for (key, value) in data:
groups[key].append(value)

numbers = [1,2,3]
my_dict = dict([(number,number*2) for number in numbers])
print(my_dict) # {1: 2, 2: 4, 3: 6}

numbers = [1, 2, 3]
my_dict = {number: number * 2 for number in numbers}
print(my_dict) # {1: 2, 2: 4, 3: 6}

# 还可以指定过滤条件
my_dict = {number: number * 2 for number in numbers if number > 1}
print(my_dict) # {2: 4, 3: 6}