1. Python中的数据类型

1.1 基础数据类型

Numeric Types — int, float, long, complex

Booleans

Strings

1.2 Containers

lists, dictionaries, sets, tuples

1.2.1 list

list在Python中几乎等价于数组，但是是可调整大小的同时也可以包容不同类型的元素。

    xs = [3, 1, 2]   # Create a list
    print xs, xs[2]  # Prints "[3, 1, 2] 2"
    print xs[-1]     
              # Negative indices count from the end of the list; prints "2"
    xs[2] = 'foo'    # Lists can contain elements of different types
    print xs         # Prints "[3, 1, 'foo']"
    xs.append('bar') # Add a new element to the end of the list
    print xs         # Prints "[3, 1, 'foo', 'bar']"
    x = xs.pop()     # Remove and return the last element of the list
    print x, xs      # Prints "bar [3, 1, 'foo']"

Slicing：除了每次访问一个列表元素，Python还提供了一种简洁的语法去访问子列表，这被称为slicing:

    nums = range(5)    
    # range is a built-in function that creates a list of integers
    print nums         # Prints "[0, 1, 2, 3, 4]"
    print nums[2:4]    
    # Get a slice from index 2 to 4 (exclusive); prints "[2, 3]"
    print nums[2:]     
    # Get a slice from index 2 to the end; prints "[2, 3, 4]"
    print nums[:2]     
    # Get a slice from the start to index 2 (exclusive); prints "[0, 1]"
    print nums[:]      
    # Get a slice of the whole list; prints ["0, 1, 2, 3, 4]"
    print nums[:-1]    
    # Slice indices can be negative; prints ["0, 1, 2, 3]"
    nums[2:4] = [8, 9] # Assign a new sublist to a slice
    print nums         # Prints "[0, 1, 8, 9, 4]"

Loops：你可以用如下方法遍历列表元素：

    animals = ['cat', 'dog', 'monkey']
    for animal in animals:
        print animal
    # Prints "cat", "dog", "monkey", each on its own line.

如果你想使用循环结构得到元素的索引以及内容，使用内置的“enumerate”方法

    animals = ['cat', 'dog', 'monkey']
    for idx, animal in enumerate(animals):
        print '#%d: %s' % (idx + 1, animal)
    # Prints "#1: cat", "#2: dog", "#3: monkey", each on its own line

列表推导：在编程的时候我们经常会想要将一种数据类型转换成另一种。举个简单的例子，思考下面这段代码，它计算了数据的平方：

    nums = [0, 1, 2, 3, 4]
    squares = []
    for x in nums:
        squares.append(x ** 2)
    print squares   # Prints [0, 1, 4, 9, 16]

你也可以使用列表推导写出更简单的代码：

    nums = [0, 1, 2, 3, 4]
    squares = [x ** 2 for x in nums]
    print squares   # Prints [0, 1, 4, 9, 16]

列表推导还可以包含判断逻辑：

    nums = [0, 1, 2, 3, 4]
    even_squares = [x ** 2 for x in nums if x % 2 == 0]
    print even_squares  # Prints "[0, 4, 16]"

1.2.2 dictionaries

字典由键值对组成。就像JAVA里面的map，以及JavaScript中的Object。使用方法如下：

    d = {'cat': 'cute', 'dog': 'furry'}  
    # Create a new dictionary with some data
    print d['cat']       # Get an entry from a dictionary; prints "cute"
    print 'cat' in d     
    # Check if a dictionary has a given key; prints "True"
    d['fish'] = 'wet'    # Set an entry in a dictionary
    print d['fish']      # Prints "wet"
    # print d['monkey']  # KeyError: 'monkey' not a key of d
    print d.get('monkey', 'N/A')  
    # Get an element with a default; prints "N/A"
    print d.get('fish', 'N/A')    
    # Get an element with a default; prints "wet"
    del d['fish']        # Remove an element from a dictionary
    print d.get('fish', 'N/A') # "fish" is no longer a key; prints "N/A"

Loops：根据字典的键很容易进行迭代。

    d = {'person': 2, 'cat': 4, 'spider': 8}
    for animal in d:
        legs = d[animal]
        print 'A %s has %d legs' % (animal, legs)
    # Prints "A person has 2 legs", "A spider has 8 legs", "A cat has 4 legs"

如果你想获得键以及对应的值，使用iteritems方法

    d = {'person': 2, 'cat': 4, 'spider': 8}
    for animal, legs in d.iteritems():
        print 'A %s has %d legs' % (animal, legs)
    # Prints "A person has 2 legs", "A spider has 8 legs", "A cat has 4 legs"

Dictionary comprehensions:和推导列表差不多，不过可以更简单的构建字典。

    nums = [0, 1, 2, 3, 4]
    even_num_to_square = {x: x ** 2 for x in nums if x % 2 == 0}
    print even_num_to_square  # Prints "{0: 0, 2: 4, 4: 16}"

1.2.3 Sets

sets是离散元的无序集合。下面举个简单的例子

    animals = {'cat', 'dog'}
    print 'cat' in animals   
    # Check if an element is in a set; prints "True"
    print 'fish' in animals  # prints "False"
    animals.add('fish')      # Add an element to a set
    print 'fish' in animals  # Prints "True"
    print len(animals)       # Number of elements in a set; prints "3"
    animals.add('cat')       
    # Adding an element that is already in the set does nothing
    print len(animals)       # Prints "3"
    animals.remove('cat')    # Remove an element from a set
    print len(animals)       # Prints "2"

Loops：迭代集合的语法和迭代列表的一样，但是当集合是无序的时候，在便利集合中的元素时不要有排序的预期。

    animals = {'cat', 'dog', 'fish'}
    for idx, animal in enumerate(animals):
        print '#%d: %s' % (idx + 1, animal)
    # Prints "#1: fish", "#2: dog", "#3: cat"

Set comprehensions:和列表以及字典一样。我们可以很简单的构建一个集合：

    from math import sqrt
    nums = {int(sqrt(x)) for x in range(30)}
    print nums  # Prints "set([0, 1, 2, 3, 4, 5])"

1.2.4 Tuples

元组是一个有序列表。在很多方面和列表一样，有一点非常重要的不同就是元组可以在字典中被用作键而列表不行。例子：

    d = {(x, x + 1): x for x in range(10)}  # Create a dictionary with tuple keys
    t = (5, 6)       # Create a tuple
    print type(t)    # Prints "<type 'tuple'>"
    print d[t]       # Prints "5"
    print d[(1, 2)]  # Prints "1"