python笔记：时间，排序

# -- coding: utf-8 --
import random
import time

num_list = []

for i in xrange(1,10000):
    num_list.append(random.randint(1, 9999))

t = time.time()
num_list.sort(lambda x,y:cmp(y,x)) #自己实现cmp函数可以实现自定义的排序器，本例是逆序
print(time.time() - t)

#python3 中取消了sort的传参，使用key做为排序依据
#把学号按先按字母正序，再按数字逆序排列，a在b前，9在1前
stu_no = ["a001","y008","b003","a009","b004"]

stu_no.sort(key=lambda x:x[1:4],reverse=True)
print(stu_no)
stu_no.sort(key=lambda x:x[0:1])
print(stu_no)

# 第二种实现方式
names = ["a001","y008","b003","a009","b004"]

a_before_z = lambda x: str.isalpha(x) and ord(x)
nine_before_zero = lambda x: str.isdigit(x) and -int(x)
result = sorted(names, 
                key=lambda x: (a_before_z(x[:1]), nine_before_zero(x[1:])
                ))
# 输出 ['a009', 'a001', 'b004', 'b003', 'y008']

val = datetime.datetime(2014,11,11,12,12,12) #2012-11-11 12:12:12

nowtime = datetime.datetime.now()
before3Day = nowtime + datetime.timedelta(days=-3)

print(val < before3Day) #注意，必须类型相同才能用小于号比较

# -- coding: utf-8 -- 
import datetime, time
temp_datetime = datetime.datetime.strptime("20090101 121212", "%Y%m%d %H%M%S")
timestamp = temp_datetime.timestamp()
print(timestamp) # 1230783132.0

temp_datetime2 = datetime.datetime.fromtimestamp(
        float("1230783132.0")
    ).strftime('%Y-%m-%d %H:%M:%S')
print(temp_datetime2) # 2009-01-01 12:12:12

#星期
def weekday(input):
    weekday_arr = [u"星期一", u"星期二", u"星期三", u"星期四", u"星期五", u"星期六", u"星期日", ]
    return weekday_arr[input]
weekday(item.timestamp.weekday())

%a -> Sun
%A -> Sunday
%b -> May
%B -> May
%c -> Sun May 24 05:21:18 1970
%d -> 24
%f -> 000000
%H -> 05
%I -> 05
%j -> 144
%m -> 05
%M -> 21
%p -> AM
%S -> 18
%U -> 21
%w -> 0
%W -> 20
%x -> 05/24/70
%X -> 05:21:18
%y -> 70
%Y -> 1970
%z -> 
%Z -> 
%% -> %

from datetime import datetime
from dateutil import tz

# METHOD 1: Hardcode zones:
from_zone = tz.gettz('UTC')
to_zone = tz.gettz('America/New_York')

# METHOD 2: Auto-detect zones:
from_zone = tz.tzutc()
to_zone = tz.tzlocal()

# utc = datetime.utcnow()
utc = datetime.strptime('2011-01-21 02:37:21', '%Y-%m-%d %H:%M:%S')

# Tell the datetime object that it's in UTC time zone since 
# datetime objects are 'naive' by default
utc = utc.replace(tzinfo=from_zone)

# Convert time zone
central = utc.astimezone(to_zone)