python-13常用内建模块

1-datetime

#1-获取当前日期和时间
from datetime import datetime
now = datetime.now() #当前时间
print(now) #2015-05-18 16:28:07.198690

#2-获取指定日期的时间
dt = datetime(2015,4,19,12,20)
print(dt) #2015-04-19 12:20:00

#3-datetime转换为timestamp
dt = datetime(2015,4,19,12,20)
print(dt.timestamp()) #1429417200.0 把datetime转换为timestamp

#某些编程语言（如Java和JavaScript）的timestamp使用整数表示毫秒数，
#这种情况下只需要把timestamp除以1000就得到Python的浮点表示方法。


#4-timestamp转换为datetime
t= 1429417200.0
print(datetime.fromtimestamp(t)) #2015-04-19 12:20:00

#5-str转换为datetime
cday = datetime.strptime('2015-6-1 18:19:59', '%Y-%m-%d %H:%M:%S')
print(cday) #2015-06-01 18:19:59

#6-datetime转换为str
now = datetime.now()
print(now.strftime('%a, %b %d %H:%M')) #Mon, May 05 16:28

#7-datetime加减
from datetime import datetime, timedelta
now = datetime.now()
now + timedelta(days=2, hours=12)

#8-本地时间转换为UTC时间

2-collections

#1-namedtuple 命名tuple
from collections import namedtuple
Point = namedtuple('Point', ['x','y'])
p = Point(1,2)
print(p.y)

#2-deque deque是为了高效实现插入和删除操作的双向列表，
from collections import deque
q = deque(['a', 'b', 'c'])
q.append('x')
q.appendleft('y')
print(q)

#3-defaultdict
#使用dict时，如果引用的Key不存在，就会抛出KeyError。
#如果希望key不存在时，返回一个默认值，就可以用defaultdict：
from collections import defaultdict
dd = defaultdict(lambda: 'N/A')
dd['key1'] = 'abc'

#4-OrderedDict 按选插入就选输出
from collections import OrderedDict
od = OrderedDict([('a', 1), ('b', 2), ('c', 3)])

#5-Counter 统计字符出现的个数：
from collections import Counter
c = Counter()
for ch in 'programming':
    c[ch] = c[ch] + 1
print(c)