GET absolute path of current file

import os
CUR_PATH = os.path.abspath(os.path.dirname(__file__))

you can combine CUR_PATH with os.path.pardir to make a parent path of CUR_PATH,
by using os.path.join(CUR_PATH, os.path.pardir).

Return the last value if a seires a value is all True, otherwise get the first value equavilent to False

rc = 1 and 2 and 3
>>> rc
3
rc2 = 'aa' and False and 0
>>> rc2

False

Make a tmp file

import tempfile
file_descriptor, file_path = tempfile.mkstemp()

Copy multiple object in a list

1.  `['obj'] * 10`
2.  `list(itertools.repeat('obj', 10))`

Else if in single expression

List Comprehension

>>> [i if i < 0 else (i, 2) if i%2 == 0 else "good" if 1 < i < 10 else 'bad' for i in range(10)]
[(0, 2), 'bad', (2, 2), 'good', (4, 2), 'good', (6, 2), 'good', (8, 2), 'good']

lambda function

complicate_lambda_func = lambda *args, **kwargs: \
    "No message" if len(args) + len(kwargs) < 2  \
    else "Yes, sir!" if ('id' in kwargs and kwargs['id'] == 'General') \
    else "There is no door for you" if 'alibaba' in args \
    else "It's already long enough, let's top here"

>>> complicate_lambda_func(1,2,3)
"It's already long enough, let's top here"
>>> complicate_lambda_func(command='fuck me', id='General')
'Yes, sir!'
>>> complicate_lambda_func("老乡", "开门啊", "我是", 'alibaba')
'There is no door for you'

看完上面两个例子，我越发觉得elif是源自于 else value if conditon 的表达方式了。
不过与elif不同的时候，上述例子的else if表达式最后一定得跟一个单纯的else语，不然报错在等着你！

If you use a comma in the end of your print statement, you will not print newline character(python2.7):

>>> for i in range(6):
...     print i,
...
0 1 2 3 4 5

More discussions

Unpacking Argument Lists

在python里你可以使用*来给函数定义可接受任意个参数。同时你也可以用*来将一个iterator unpack成一系列args传给函数!
str, list, tuple, dict都可以使用这个技术，不过dict出来的参数顺序可能是乱的，因为hash的特性。 

def print_args(*args):
    print " -- ".join(map(str, args))

# Str
>>> print_args(*"Monster")
M -- o -- n -- s -- t -- e -- r

# List
>>> print_args(*range(5))
0 -- 1 -- 2 -- 3 -- 4

# Tuple
>>> print_args(*("Harry Poter", "Princess White"))
Harry Poter -- Princess White

# Dict
>>> print_args(*{"a":1, "b":2, "c":3, "d":4})
a -- c -- b -- d

Unpacking keyword args

Mapping object可以用**来unpacking, 但是key必须是字符串。 

def print_kwargs(**kwargs):
    for i, j in kwargs.items():
        print i, '\t', j

>>> print_kwargs(**{"a": 1, "b": 2})
a   1
b   2

你也可以自定义一个对象，只要它有__getitem__和keys两个方法并且有符合规范的处理逻辑， 它也能被**unpacking.
stackoverflow相关讨论

class MyMapping(object):
    def __getitem__(self, key):
        if int(key) in range(5):
            return "Mapping and unpacking!"

    def keys(self):
        return map(str, range(5))

>>> my_mapping = MyMapping()
>>> print_kwargs(**my_mapping)

1   Mapping and unpacking!
0   Mapping and unpacking!
3   Mapping and unpacking!
2   Mapping and unpacking!
4   Mapping and unpacking!

调用运算结果的属性。

在Python里，如何将一个函数名指给一个运算结果的属性？
你只需要将运算结果用()包裹起来，接着便可把()当成一个对象，调用它的属性了！ 

from datetime import datetime
unix_start_date = datetime.fromtimestamp(0)
current_date = datetime.now()
delta_date = (current_date - unix_start_date).days

Format String with dictionray variables

 my_dict = {
    "my_name": "Liu ting",
    "my_age": 13,
    "my_boss": "Liu lao gen",
    "adjective1": "Handsome",
    "adjective2": "Dirty",
    "python_toy": set(["Secondary life", "Love me", "You bold bold!"]), {"Idol": "DggggJ", "Hijastra": "XOK"}, ["P", "Y", "T", "H", "O", "N"]),
}

print "大家好，我叫{my_name}, 今年{my_age}岁，我的老板叫{my_boss}, 他有时候{adjective1},有时候{adjective2}, 我最爱的玩具是: \n\n{python_toy}".format(**my_dict)

对原函数/类方法进行inspect/审查的decorator

 import random

def function_inspector(func):
    def new_func(*args, **kwargs):
        Lucky_number = [6, 7, 8, 9]
        result = func(*args, **kwargs)
        if type(result) == int and result in Lucky_number:
            return result, "You are Lucky"
        else:
            return result
    return new_func

@function_inspector
def lottery():
     return random.choice(range(10))

>>> lottery()
3
>>> lottery()
(8, 'You are Lucky')


def method_inspector(method):
    BANNED_WEBSITES = ['google', 'facebook', 'youtube', 'twitter']
    BANNED_WORDS = ['法轮功', '共产党']

    def new_method(self, *args, **kwargs):  # 此处的self参数是为了对类方法进行inspect所加
        if getattr(self, 'name', None) in BANNED_WEBSITES:
            return "404 网站无法访问"
        result = method(self, *args, **kwargs)
        for i in result:
            if type(i) != str:
                continue
            for banned_word in BANNED_WORDS:
                if banned_word in i:
                    return "该网站含有不恰当内容"
        return result

    return new_method

将任意字符串变成全局变量

  target_string = raw_input()
  command_1 = 'global %s' % target_string
  exec(command_1)
  globals()[target_string] = your_value

在全局变量中执行字符串命令

exec默认是在locals()变量环境里执行语句，如果想要在全局变量环境里执行的话

你需要使用 exec 'my_command' in globals()
如果需要在本地和global的混合环境里执行命令，你使用exec 'my_command' in globals(), locals()

相关讨论 官方文档

查看一个OBJ的代码依赖关系

import traceback
# inside something
for i in traceback.extract_stack:
    print i

查看一个变量是否是函数

hasattr(var, '__call__')

反转变量True False属性

a = "Hi"
a = not a
a
False
a = not a
a
True

小心浮点数

在python2.7里，你指定一个值，st=0.7999999999999，你调用该值，得到0.7999999999999， 你print它， 你得到的是。。0.8

让你的程序运行指定的时长

import signal
import sys

def terminate_func(*args, **params):
    # do your final things here before exit
    sys.exit(0)

signal.signal(signal.SIGALRM, terminate_func)
signal.alarm(100)   # after 100 seconds of running, execute terminate_func

The running time isn't precise, like signal.alarm(100) could use 100.00013332 seconds. 注意，使用SIGALRM来绑定func时，func需要用*args和**kwargs来接受任意参数，不然会报错

python2做除法时直接求浮点数

>>>from __future__ import division
>>>2/3
0.6666666666666666
>>>3/3
1.0

在python 3中，此种除法方式是default行为

将url中特殊字符(% + alphanum表示的那些字符)进行转换

import urllib
converted_str = urllib.unquote(raw_url_str)

将一个大列表以n的跨度切割成若干小列表

new_list = [raw_list[i:i+n] for i in range(0, len(raw_list), n)]

使用文件名字符进行from m import *操作

agent = importlib.import_module(module_name)
globals().update(vars(agent))

将一个python数据转换成json格式

import json
converted_json_data = json.dumps(raw_python_data)

让一个python文件打印自己的所有内容！

print open(__file__).read()

在cent-OS上给python安装mysql模块

# First you shall install mysql-devel, such as:
yum install mysql-devel
# Then install mysql module in python
pip install mysql

一句话反转字典键值对

inv_map = {v:k for k,v in my_dict.items()}

简单粗暴解决各类utf-8编码问题

# coding: utf-8
import sys
reload(sys)
sys.setdefaultencoding("utf-8")

查看当前python进程使用的内存大小

import resource
mem_usage = resource.getrusage(resource.RUSAGE_SELF)
print mem_usage.ru_maxrss

# OSX 下的单位是byte, 而Linux下的单位是kilobyte
# 将RUSAGE_SELF 换成 RUSAGE_CHILDREN 来查看子进程的内存占用

判断一个对象的大小

# 方法1
import sys
sys.getsizeof(object[, default])

# 方法2
object.__sizeof__()

判断一个对象是否是iterable

if hasattr(my_obj, '__iter__')

获得当前文件路径

import os
os.path.dirname(os.ptah.abspath(__file__))      # 文件存储路径
os.getcwd()                                     # 当前所在的执行路径

检测一个对象是否是字符串(包括普通字符和unicode字符)

isinstance(obj, basestring)

Write several statement in a line.(using ;)

salary=1000; bonus=1200; print salary + bonus

Log detailed error info without exit python process

import traceback
import sys
try:
    eval('Your Arbitary Code here')
except:
    print 'This is diy error log'
    print traceback.format_exc()
    print sys.exc_info()

SyntaxError can only be caught when the code executed in eval or exec. Try remove eval and quote, you'll know what I mean.

Arithmatic operation

  • convert a string coded in base-n system into decimal number

    int(str, base_n)
e.g: int('0xAE', 16)

DATA STRUCTURE

SET OPERATION

UNION               s | t           #  all elements in s and t, except duplicate
INTERSECTION        s & t           #  elements that are in s and t
DIFERENCE           s - t           #  element in s but not in t
SYMMETRIC_DIFFER    s ^ t           #  equal to (s - t) | (t - s), means that element in t or s that are not appeared in both set

DATETIME AND TIME

获取当前某个日期午夜的datetime对象

# 假定我们拿到了传入的datetime_obj
from datetime import datetime
mid_night = datetime.combine(datetime_obj.date(), datetime.min.time())

# 一个判断传入字符串是否是当日零点的函数
def is_midnight(date_str, date_format="%Y-%m-%d %H:%M:%S"):
    """检查字符串是否是当日的午夜。"""
    datetime_obj = datetime.strptime(date_str, date_format)
    datetime_midnight = datetime.combine(datetime_obj.date(), datetime.min.time())
    return datetime_obj == datetime_midnight

获取当前自然日的日期字符串

from datetime import datetime
natural_date = str(datetime.now().date())

Formate Year/Month/Day without 0 padding

    import datetime
    "{dt.year}{dt.month}{dt.day}".format(dt=datetime.datetime.now())

This will delete the key-value pair if key in my_dict, otherwise defualt_value will be returned, so you won't get an error when key isn't in my_dict

快速将字符串解析成datetime对象

需要先安装py-dateutil

from dateutil import parser
datetime_obj = parser.parse(datetime_str, fuzzy=True)

fuzzy=True会开启模糊模式，忽略一些parser不能识别的字符

快速打印格式化的当前年月日和时分秒

import time
time.strftime('%F %T')
# %F 是年月日在time模块里的快捷表示，%T是时分秒的快捷表示, 样例：2015-01-01 00:00:00

  • if List_A exists, iter over List_A, otherwise iter over List_B

      for i in List_A or List_B:
      print i

  • delete one item from a dict

      my_dict.pop(key, default_value)

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