Python Tips and Traps(一)

1、如果想得到一个列表的index和内容，可以通过enumerate快速实现

drinks = ['coffee','tea', 'milk', 'water']
for index, drink in enumerate(drinks):
    print ('Item {} is {}'.format(index, drink))
#Result
# Item 0 is coffee
# Item 1 is tea
# Item 2 is milk
# Item 3 is water

2、Python 中的set， 是一个无序不重复元素集，可以非常方便的进行关系测试和消除重复元素

# deduplicate a list fast
print (set(['ham', 'eggs','bacon','ham']))
# Result
# {'ham', 'eggs', 'bacon'}

# compare list to find difference/similarities 
# {} without "key":"value" pairs makes a set
menu = {'pancakes', 'ham', 'eggs', 'bacon'}
new_menu = {'coffee', 'ham', 'eggs', 'bagels', 'bacon'}

new_items = new_menu.difference(menu)
print ('try our new', ', '.join(new_items))

# Result: try our new coffee, bagels

discontinued_items = menu.difference(new_menu)
print ('sorry, we no longer have', ', '.join(discontinued_items))

# Result: sorry, we no longer have panckes

old_items = new_menu.intersection(menu)
print ('Or get the same old', ', '.join(old_items))

# Result: Or ger the same old eggs, ham, bacon

full_menu = new_menu.union(menu)
print ('At one time or another, we have served ', ','.join(full_menu))

3、namedtuple    生成可以使用名字来访问元素内容的tuple 子类，非常方便

import collectionshttp:
LightObject = collections.namedtuple('LightObject', ['shortname', 'otherprop'])
n = LightObject(shortname = 'something', otherprop = 'something else')
n.shortname  # something

4、deque 双段队列，最大好处就是可以从头部添加和删除对象 popleft()、 appendleft()

import collections
d = collections.deque('123456')
print d.popleft()  # '1'
d.appendleft('7')
print d #  deque(['7','2','3','4','5','6'])

5、Counter 同样是collections 中的，主要用来计数

import collections
c = collections.Counter('abcab')
print c #Couner({'a':2,'b':2,'c':1}

elements 方法返回一个迭代器，将生成Counter 知道的所有元素；most_common（n）生成一个序列，包含最常用的输入值及相应计数