Python骚操作

遍历列表

array = [1, 2, 3, 4, 5]

for i in range(len(array)):
    print (i, array[I])

# Pythonic 
for i, item in enumerate(array):
    print (i, item)

对列表的操作

array = [1, 2, 3, 4, 5]

new_array = []
for item in array:
    new_array.append(str(item))

# Pythonic
new_array = [str(item) for item in array]

# Generator
new_array = (str(item) for item in array)

# 函数式
new_array = map(str, array)

列表推导

# 生成列表
[ i*i for i in range(10) if i % 2 == 0 ]
# 生成集合
{ i*i for i in range(10) if i % 2 == 0 }
# 生成字典
{ i:i for i in range(10) if i % 2 == 0 }

上下文管理器

file = open('file', 'w')
file.write(123)
file.close()

# Pythonic
with open('file', 'w') as file:
    file.write(123)

条件判断

if x is True:
    y = 1
else:
    y = -1

# Pythonic
y = 1 if x is True else -1

构造矩阵

y = [0 for _ in range(100000000)]
# Pythonic
y = [0] * 100000000

装饰器

def logic(x):
    if x < 0:
        return False
    print (x)
    return True

#Pythonic
def check_gt_zero(func):
    def wrapper(x):
        if x < 0:
            return False
        return func(x)
    return wrapper 

@check_gt_zero
def logic(x):
    print (x)
    return True

变量交换

temp = y
y = x
x = temp

# Pythonic
x, y = y, x

切片

array = [1, 2, 3, 4, 5]

l = len(array)
for i in range(l/2):
    temp = array[l - i - 1]
    array[l - i - 1] = array[I]
    array[i] = temp

array = list(reversed(array))
# Pythonic
array = array[::-1]

读取文件

CHUNK_SIZE = 1024

with open('test.json') as f:
    chunk = f.read(CHUNK_SIZE)
    while chunk:
        if chunk:
            print(chunk)
        chunk = f.read(CHUNK_SIZE)

from functools import partial
# Pythonic
with open('test.json') as f:
    for piece in iter(partial(f.read, CHUNK_SIZE), ''):
        print (piece)

# Lambda
with open('test.json') as f:
    for piece in iter(lambda: f.read(CHUNK_SIZE), ''):
        print (piece)

for-else和try-else语法

is_for_finished = True

try:
    for item in array:
        print (item)
        # raise Exception
except:
    is_for_finished = False

if is_for_finished is True:
    print ('complete')

# Pythonic
for item in array:
    print (item)
    # raise Exception
else:
    print ('complete')

try:
    print ('try')
    # raise Exception
except Exception:
    print ('exception')
else:
    print ('complete')

函数参数解压

def draw_point(x, y):
    # do some magic

point_foo = (3, 4)
point_bar = {'y': 3, 'x': 2}

draw_point(*point_foo)
draw_point(**point_bar)

列表/元组解压

first, second, *rest = (1,2,3,4,5,6,7,8)

"Print To"语法

print ("hello world", file=open("myfile", "w"))

字典缺省值

d = {}

try:
    d['count'] = d['count'] + 1
except KeyError:
    d['count'] = 0

# Pythonic
d['count'] = d.get('count', 0) + 1

链式比较符

if x < 100 and x > 0:
    print(x)

# Pythonic
if 0 < x < 100:
    print(x)

多行字符串

s = ("longlongstringiii"
    "iiiiiiiii"
    "iiiiiii")

in表达式

if 'string'.find('ring') > 0:
    print ('find')

# Pythonic
if 'ring' in 'string':
    print ('find')

for r in ['ring', 'ring1', 'ring2']:
    if r == 'ring':
        print ('find')

# Pythonic
if 'ring' in ['ring', 'ring1', 'ring2']:
    print('find')

字符串连接

array = ['a', 'b', 'c', 'd', 'e']
s = array[0]
for char in array[1:]:
    s += ',' + char

# Pythonic
s = ','.join(array)

列表合并字典

keys = ['a', 'b', 'c']
values = [1, 2, 3]

d = {}
for key, value in zip(keys, values):
    d[key] = value

# Better
d = dict(zip(keys, values))

# Pythonic
d = {key: value for key, value in zip(keys, values)}

all和any

flag = True
for cond in conditions:
    if cond is False:
        flag = False
        break
# Pythonic
flag = all(conditions)

flag = False
for cond in conditions:
    if cond is True:
        flag = True
        break
# Pythonic
flag = any(conditions)

or

not_null_string = '' or 'string1' or 'string2'
# string1

方法提取

for item in ['b', 'c']:
    array.append(item)
# Faster
append = array.append
for item in ['b', 'c']:
    append(item)

单例模式

from [module] import [single_instance]

用<>代替!=

In [1]: from __future__ import barry_as_FLUFL

In [2]: 1 == 1
Out[2]: True

In [3]: 1 != 1
  File "<ipython-input-3-1ec724d2c3b1>", line 1
    1 != 1
       ^
SyntaxError: invalid syntax

In [4]: 1 <> 1
Out[4]: False

格式化一个json文件

python -m json.tool test.json
echo '{"json":"obj"}' | python -m json.tool # 管道

开启本地目录的HTTP服务器

python3 -m http.server 8080