1. More on List
a) Functional Programming Tools：
filter(function, sequence): returns a sequence consisting of those items from the sequence for which function(item) is true.
如果sequence是string或tuple，则filter返回string或tuple；否则返回list
>>> def f(x): return x % 2 != 0 and x % 3 != 0
>>> filter(f, range(2, 25))
[5, 7, 11, 13, 17, 19, 23]
map(function, sequence): calls function(item) for each of the sequence's items and returns a list of the return values.
>>> def cube(x): return x*x*x
>>> map(cube, range(1, 11))
[1, 8, 27, 64, 125, 216, 343, 512, 729, 1000]
可以传多个sequence。但如果sequences长度不同，则短sequence对应于长sequence的items被视为None. => 如果做与None不符的操作会产生错误.
>>> seq = range(8)
>>> def add(x, y): return x+y
>>> map(add, seq, seq)
[0, 2, 4, 6, 8, 10, 12, 14]
reduce(function, sequence): returns a single value constructed by calling the binary function function on the first two items of the sequence, then on the result and the next item, and so on.
>>> def add(x,y): return x+y
>>> reduce(add, range(1, 11))
55
b) List Comprehensions
一种比map(), filter() and/or lambda 更为“精妙”的产生List的方法。
List Comprehension: [expression for ... [for ...][ if...]]. [for ...][ if...]] means 0 or more
如果expression是一个tuple，则必须括起来
>>> vec = [2, 4, 6]
>>> [3*x for x in vec if x > 3]
[12, 18]
>>> [[x,x**2] for x in vec] #expression is tuple
[[2, 4], [4, 16], [6, 36]]
>>> [(x, x**2) for x in vec]
[(2, 4), (4, 16), (6, 36)]
# operate on two lists
>>> vec1 = [2, 4, 6]
>>> vec2 = [4, 3, -9]
>>> [x+y for x in vec1 for y in vec2]
[6, 5, -7, 8, 7, -5, 10, 9, -3]
>>> [vec1[i]*vec2[i] for i in range(len(vec1))]
[8, 12, -54]
2. del statement
通过a) index，b) slices 删除list中的元素。也可删除变量
3. Tuple
A tuple consists of a number of values separated by commas.
Tuple允许嵌套，单个tuple输入时无需加括号，但如果作为一个元素用在其他表达式中，则需要加括号。
与string一样，tuple中的元素值也是不可更改的，但tuple可以包含mutable的对象，如list.
>>> empty = ()
>>> singleton = 'hello', # <-- note trailing comma
>>> len(empty)
0
>>> len(singleton)
1
>>> singleton
('hello',)
tuple packing: such as t = 12345, 54321, 'hello!', the values 12345, 54321 and 'hello!' are packed together in a tuple.
sequence unpacking: such as x, y, z = t. 左边变量列表中的元素个数必须与右边的tuple中元素个数相同
multiple assignment是tuple packing和sequence unpacking的组合
4. Sets
元素不允许重复的无序集合。支持并集，交集，差集和对称差集(symmetric difference)等集合操作
>>> basket = ['apple', 'orange', 'apple', 'pear', 'orange', 'banana']
>>> fruit = set(basket) # create a set without duplicates
>>> fruit
set(['orange', 'pear', 'apple', 'banana'])
>>> 'orange' in fruit # fast membership testing
True
>>> 'crabgrass' in fruit
False
>>> # Demonstrate set operations on unique letters from two words
>>> a = set('abracadabra')
>>> b = set('alacazam')
>>> a # unique letters in a
set(['a', 'r', 'b', 'c', 'd'])
>>> a - b # letters in a but not in b
set(['r', 'd', 'b'])
>>> a | b # letters in either a or b
set(['a', 'c', 'r', 'd', 'b', 'm', 'z', 'l'])
>>> a & b # letters in both a and b
set(['a', 'c'])
>>> a ^ b # letters in a or b but not both
set(['r', 'd', 'b', 'm', 'z', 'l'])
5. Dictionaries
dictionary = {key:value, key:value,...}
dictionaries中，key可以为string，number，tuple(tuple中不能包含mutable的对象，如list)。key是唯一的，当对其中一个key对应的元素赋值时，之前保存的值会被冲掉。用del可以删除dict中的key:value元素，如del dict["key1"]
key()返回包含所有key的list，无序。
has_key() or in 查看某个key是否包含在dict中
dict() 从key-value以tuple方式存储的list中构建dictionary
>>> dict([('sape', 4139), ('guido', 4127), ('jack', 4098)])
{'sape': 4139, 'jack': 4098, 'guido': 4127}
>>> dict([(x, x**2) for x in (2, 4, 6)]) # use a list comprehension
{2: 4, 4: 16, 6: 36}
>>> dict(sape=4139, guido=4127, jack=4098)
{'sape': 4139, 'jack': 4098, 'guido': 4127}
6. Looping Techniques
a) dictionaries
用 iteritems() 同时获得key和value
b) one sequence
用 enumerate() 同时获得index和value
c) two or more sequences
zip(seq1, seq2...)
d) a sequence in reversed
reversed(seq)
e) a sequence in sorted
sorted(seq): 生成一个新的有序的sequence
#dictionary
>>> knights = {'gallahad': 'the pure', 'robin': 'the brave'}
>>> for k, v in knights.iteritems():
print k, v
gallahad the pure
robin the brave
# a sequence
>>> for i, v in enumerate(['tic', 'tac', 'toe']):
print i, v
0 tic
1 tac
2 toe
# two or more sequences
>>> questions = ['name', 'quest', 'favorite color']
>>> answers = ['lancelot', 'the holy grail', 'blue']
>>> for q, a in zip(questions, answers):
print 'What is your %s? It is %s.' % (q, a)
What is your name? It is lancelot.
What is your quest? It is the holy grail.
# a sequence in reversed order
>>> for i in reversed(xrange(1,10,2)):
print i
9
7
5
3
1
# a sequence in sorted order
>>> basket = ['apple', 'orange', 'apple', 'pear', 'orange', 'banana']
>>> for f in sorted(set(basket)):
print f
apple
banana
orange
pear