Python4：DataStructure

1.Introduction

数据结构基本上就是可以处理一些数据的结构。或者说，它们是用来存储一组相关数据的。在Python中有三种内建的数据结构——列表、元组和字典。

2.列表

list是处理一组有序项目的数据结构，即可以在一个列表中存储一个序列的项目。假想有一个购物列表，上面记载着要买的东西，就容易理解列表了。只不过在你的购物表上，可能每样东西都独自占有一行，而在Python中，在每个项目之间用逗号分割。
列表中的项目应该包括在方括号中，这样Python就知道你是在指明一个列表。一旦创建了一个列表，就可以添加、删除或是搜索列表中的项目。由于可以增加或删除项目，我们说列表是可变的数据类型，即这种类型是可以被改变的。

#using_list.py
#This is my shopping list
shoplist =['apple','mango','carrot','banana'];
print 'i have', len(shoplist), 'items to purchase';

print 'There items are :';
for item in shoplist:
    print item;

print '\n I also have to buy rice.';

shoplist.append('rice');
print 'My shopping list is now ', shoplist;

print 'I will sort my list now';
shoplist.sort();
print 'Sorted shopping list is ',shoplist;

print 'The first item I will buy is',shoplist[0];
olditem = shoplist[0];
del shoplist[0];
print 'I bought the',olditem;
print 'My shopping list is now ',shoplist;

3.元组

元组和列表十分类似，只不过元组和字符串一样是不可变的，即不能修改元组。元组通过圆括号中用逗号分割的项目定义。元组通常用在使语句或用户定义的函数能够安全地采用一组值的时候，即被使用的元组的值不会改变。

#using_tuple.py
zoo = ('wolf','elephant','penguin');
print 'number of animals in the zoo is ', len(zoo);

new_zoo = ['monkey','dolphin',zoo];
print 'number of animals in the new zoo is ', len(new_zoo);

print 'All animals in the new zoo are ', new_zoo;
print 'Animals brought from old zoo are :',new_zoo[2];
print 'Last animal brought from old zoo is :',new_zoo[2][2];

4.字典

字典类似于通过联系人名字查找地址和联系人详细情况的地址簿，即，把键（名字）和值（详细情况）联系在一起。注意，键必须是唯一的。
键值对在字典中以这样的方式标记：d = {key1 : value1, key2 : value2 }。注意它们的键/值对用冒
号分割，而各个对用逗号分割，所有这些都包括在花括号中。
记住字典中的键/值对是没有顺序的。如果想要一个特定的顺序，那么应该在使用前对它们排序。字典是dict类的实例/对象。

#using_dict.py
#ab = address book
ab = {'Swaroop'  :'[email protected]',
      'Larry'    :'[email protected]',
      'Matsumoto':'[email protected]',
      'Spammer'  :'[email protected]'
      };
print "Swaroop's address is %s :", ab['Swaroop'];
#adding a key/value pair
ab['Guido'] = '[email protected]';

#deleting key/value pair
del ab['Spammer'];
print '\nThere are %d contacts in the address-book\n' % len(ab);

for name, address in ab.items():
    print 'contact %s at %s' % (name,address);

if 'Guido' in ab:
    print "\nGuido's address is %s" % ab['Guido'];

5.序列

列表、元组和字符串都是序列。序列的两个主要特点是索引操作符和切片操作符。索引操作符让我们可以从序列中抓取一个特定项目。切片操作符让我们能够获取序列的一个切片，即一部分序列。

#using_sqe.py
shoplist = ['apple','mango','carrot','banana'];

# Indexing or 'Subscription' operation
print 'Item 0 is',  shoplist[0]
print 'Item 1 is',  shoplist[1]
print 'Item 2 is',  shoplist[2]
print 'Item 3 is',  shoplist[3]
print 'Item -1 is', shoplist[-1]
print 'Item -2 is', shoplist[-2]

# Slicing on a list
print 'Item 1 to 3 is',    shoplist[1:3]
print 'Item 2 to end is',  shoplist[2:]
print 'Item 1 to -1 is',   shoplist[1:-1]
print 'Item start-end is', shoplist[:]

# Slicing on a string
name = 'swaroop'
print 'characters 1 to 3 is',    name[1:3]
print 'characters 2 to end is',  name[2:]
print 'characters 1 to -1 is',   name[1:-1]
print 'characters start-end is', name[:]

6.reference

当创建一个对象并给它赋一个变量的时候，这个变量仅仅引用那个对象，而不是表示这个对象本身！也就是说，变量名指向你计算机中存储那个对象的内存。这称作名称到对象的绑定。一般说来，不需要担心这个，只是在引用上有些细微的效果需要注意。示例如下：

#using_reference.py
print 'Simple Assignment'
shoplist = ['apple', 'mango', 'carrot', 'banana']
mylist = shoplist # mylist is just another name pointing to the same object!
del shoplist[0]
print 'shoplist is', shoplist
print 'mylist is', mylist
# notice that both shoplist and mylist both print the same list without
# the 'apple' confirming that they point to the same object
print 'Copy by making a full slice'
mylist = shoplist[:] # make a copy by doing a full slice
del mylist[0] # remove first item
print 'shoplist is', shoplist
print 'mylist is', mylist
# notice that now the two lists are different

7.String

# String_method.py
name = 'Swaroop' # This is a string object
if name.startswith('Swa'):
    print 'Yes, the string starts with "Swa"'
if 'a' in name:
    print 'Yes, it contains the string "a"'
if name.find('war') != -1:
    print 'Yes, it contains the string "war"'
    delimiter = '_*_'
    mylist = ['Brazil', 'Russia', 'India', 'China']
    print delimiter.join(mylist)