# Single line comments start with a hash. # 单行注释由一个井号开头。 """ Multiline strings can be written using three "'s, and are often used as comments 三个双引号(或单引号)之间可以写多行字符串, 通常用来写注释。 """ #################################################### ## 1\. Primitive Datatypes and Operators ## 1\. 基本数据类型和操作符 #################################################### # You have numbers # 数字就是数字 3 #=> 3 # Math is what you would expect # 四则运算也是你所期望的那样 1 + 1 #=> 2 8 - 1 #=> 7 10 * 2 #=> 20 35 / 5 #=> 7 # Division is a bit tricky. It is integer division and floors the results # automatically. # 除法有一点棘手。 # 对于整数除法来说,计算结果会自动取整。 5 / 2 #=> 2 # To fix division we need to learn about floats. # 为了修正除法的问题,我们需要先学习浮点数。 2.0 # This is a float 2.0 # 这是一个浮点数 11.0 / 4.0 #=> 2.75 ahhh...much better 11.0 / 4.0 #=> 2.75 啊……这样就好多了 # Enforce precedence with parentheses # 使用小括号来强制计算的优先顺序 (1 + 3) * 2 #=> 8 # Boolean values are primitives # 布尔值也是基本数据类型 True False # negate with not # 使用 not 来取反 not True #=> False not False #=> True # Equality is == # 等式判断用 == 1 == 1 #=> True 2 == 1 #=> False # Inequality is != # 不等式判断是用 != 1 != 1 #=> False 2 != 1 #=> True # More comparisons # 还有更多的比较运算 1 True 1 > 10 #=> False 2 True 2 >= 2 #=> True # Comparisons can be chained! # 居然可以把比较运算串连起来! 1 True 2 False # Strings are created with " or ' # 使用 " 或 ' 来创建字符串 "This is a string." 'This is also a string.' # Strings can be added too! # 字符串也可以相加! "Hello " + "world!" #=> "Hello world!" # A string can be treated like a list of characters # 一个字符串可以视为一个字符的列表 # (译注:后面会讲到“列表”。) "This is a string"[0] #=> 'T' # % can be used to format strings, like this: # % 可以用来格式化字符串,就像这样: "%s can be %s" % ("strings", "interpolated") # A newer way to format strings is the format method. # This method is the preferred way # 后来又有一种格式化字符串的新方法:format 方法。 # 我们推荐使用这个方法。 "{0} can be {1}".format("strings", "formatted") # You can use keywords if you don't want to count. # 如果你不喜欢数数的话,可以使用关键字(变量)。 "{name} wants to eat {food}".format(name="Bob", food="lasagna") # None is an object # None 是一个对象 None #=> None # Don't use the equality `==` symbol to compare objects to None # Use `is` instead # 不要使用相等符号 `==` 来把对象和 None 进行比较, # 而要用 `is`。 "etc" is None #=> False None is None #=> True # The 'is' operator tests for object identity. This isn't # very useful when dealing with primitive values, but is # very useful when dealing with objects. # 这个 `is` 操作符用于比较两个对象的标识。 # (译注:对象一旦建立,其标识就不会改变,可以认为它就是对象的内存地址。) # 在处理基本数据类型时基本用不上, # 但它在处理对象时很有用。 # None, 0, and empty strings/lists all eval(1) #li is now [1] #li 现在是 [1] li.append(2) #li is now [1, 2] #li 现在是 [1, 2] li.append(4) #li is now [1, 2, 4] #li 现在是 [1, 2, 4] li.append(3) #li is now [1, 2, 4, 3] #li 现在是 [1, 2, 4, 3] # Remove from the end with pop # 使用 pop 来移除最后一个元素 li.pop() #=> 3 and li is now [1, 2, 4] #=> 3,然后 li 现在是 [1, 2, 4] # Let's put it back # 我们再把它放回去 li.append(3) # li is now [1, 2, 4, 3] again. # li 现在又是 [1, 2, 4, 3] 了 # Access a list like you would any array # 像访问其它语言的数组那样访问列表 li[0] #=> 1 # Look at the last element # 查询最后一个元素 li[-1] #=> 3 # Looking out of bounds is an IndexError # 越界查询会产生一个索引错误 li[4] # Raises an IndexError # 抛出一个索引错误 # You can look at ranges with slice syntax. # (It's a closed/open range for you mathy types.) # 你可以使用切片语法来查询列表的一个范围。 # (这个范围相当于数学中的左闭右开区间。) li[1:3] #=> [2, 4] # Omit the beginning # 省略开头 li[2:] #=> [4, 3] # Omit the end # 省略结尾 li[:3] #=> [1, 2, 4] # Remove arbitrary elements from a list with del # 使用 del 来删除列表中的任意元素 del li[2] # li is now [1, 2, 3] # li 现在是 [1, 2, 3] # You can add lists # 可以把列表相加 li + other_li #=> [1, 2, 3, 4, 5, 6] - Note: li and other_li is left alone #=> [1, 2, 3, 4, 5, 6] - 请留意 li 和 other_li 并不会被修改 # Concatenate lists with extend # 使用 extend 来合并列表 li.extend(other_li) # Now li is [1, 2, 3, 4, 5, 6] # 现在 li 是 [1, 2, 3, 4, 5, 6] # Check for existence in a list with in # 用 in 来检查是否存在于某个列表中 1 in li #=> True # Examine the length with len # 用 len 来检测列表的长度 len(li) #=> 6 # Tuples are like lists but are immutable. # 元组很像列表,但它是“不可变”的。 tup = (1, 2, 3) tup[0] #=> 1 tup[0] = 3 # Raises a TypeError # 抛出一个类型错误 # You can do all those list thingies on tuples too # 操作列表的方式通常也能用在元组身上 len(tup) #=> 3 tup + (4, 5, 6) #=> (1, 2, 3, 4, 5, 6) tup[:2] #=> (1, 2) 2 in tup #=> True # You can unpack tuples (or lists) into variables # 你可以把元组(或列表)中的元素解包赋值给多个变量 a, b, c = (1, 2, 3) # a is now 1, b is now 2 and c is now 3 # 现在 a 是 1,b 是 2,c 是 3 # Tuples are created by default if you leave out the parentheses # 如果你省去了小括号,那么元组会被自动创建 d, e, f = 4, 5, 6 # Now look how easy it is to swap two values # 再来看看交换两个值是多么简单。 e, d = d, e # d is now 5 and e is now 4 # 现在 d 是 5 而 e 是 4 # Dictionaries store mappings # 字典用于存储映射关系 empty_dict = {} # Here is a prefilled dictionary # 这是一个预先填充的字典 filled_dict = {"one": 1, "two": 2, "three": 3} # Look up values with [] # 使用 [] 来查询键值 filled_dict["one"] #=> 1 # Get all keys as a list # 将字典的所有键名获取为一个列表 filled_dict.keys() #=> ["three", "two", "one"] # Note - Dictionary key ordering is not guaranteed. # Your results might not match this exactly. # 请注意:无法保证字典键名的顺序如何排列。 # 你得到的结果可能跟上面的示例不一致。 # Get all values as a list # 将字典的所有键值获取为一个列表 filled_dict.values() #=> [3, 2, 1] # Note - Same as above regarding key ordering. # 请注意:顺序的问题和上面一样。 # Check for existence of keys in a dictionary with in # 使用 in 来检查一个字典是否包含某个键名 "one" in filled_dict #=> True 1 in filled_dict #=> False # Looking up a non-existing key is a KeyError # 查询一个不存在的键名会产生一个键名错误 filled_dict["four"] # KeyError # 键名错误 # Use get method to avoid the KeyError # 所以要使用 get 方法来避免键名错误 filled_dict.get("one") #=> 1 filled_dict.get("four") #=> None # The get method supports a default argument when the value is missing # get 方法支持传入一个默认值参数,将在取不到值时返回。 filled_dict.get("one", 4) #=> 1 filled_dict.get("four", 4) #=> 4 # Setdefault method is a safe way to add new key-value pair into dictionary # Setdefault 方法可以安全地把新的名值对添加到字典里 filled_dict.setdefault("five", 5) #filled_dict["five"] is set to 5 #filled_dict["five"] 被设置为 5 filled_dict.setdefault("five", 6) #filled_dict["five"] is still 5 #filled_dict["five"] 仍然为 5 # Sets store ... well sets # set 用于保存集合 empty_set = set() # Initialize a set with a bunch of values # 使用一堆值来初始化一个集合 some_set = set([1,2,2,3,4]) # some_set is now set([1, 2, 3, 4]) # some_set 现在是 set([1, 2, 3, 4]) # Since Python 2.7, {} can be used to declare a set # 从 Python 2.7 开始,{} 可以用来声明一个集合 filled_set = {1, 2, 2, 3, 4} # => {1, 2, 3, 4} # (译注:集合是种无序不重复的元素集,因此重复的 2 被滤除了。) # (译注:{} 不会创建一个空集合,只会创建一个空字典。) # Add more items to a set # 把更多的元素添加进一个集合 filled_set.add(5) # filled_set is now {1, 2, 3, 4, 5} # filled_set 现在是 {1, 2, 3, 4, 5} # Do set intersection with & # 使用 & 来获取交集 other_set = {3, 4, 5, 6} filled_set & other_set #=> {3, 4, 5} # Do set union with | # 使用 | 来获取并集 filled_set | other_set #=> {1, 2, 3, 4, 5, 6} # Do set difference with - # 使用 - 来获取补集 {1,2,3,4} - {2,3,5} #=> {1, 4} # Check for existence in a set with in # 使用 in 来检查是否存在于某个集合中 2 in filled_set #=> True 10 in filled_set #=> False #################################################### ## 3\. Control Flow ## 3\. 控制流 #################################################### # Let's just make a variable # 我们先创建一个变量 some_var = 5 # Here is an if statement. Indentation is significant in python! # prints "some_var is smaller than 10" # 这里有一个条件语句。缩进在 Python 中可是很重要的哦! # 程序会打印出 "some_var is smaller than 10" # (译注:意为“some_var 比 10 小”。) if some_var > 10: print "some_var is totally bigger than 10." # (译注:意为“some_var 完全比 10 大”。) elif some_var prints out "x is 5 and y is 6" and returns 11 # (译注:意为“x 是 5 而且 y 是 6”,并返回 11) # Another way to call functions is with keyword arguments # 调用函数的另一种方式是传入关键字参数 add(y=6, x=5) # Keyword arguments can arrive in any order. # 关键字参数可以以任意顺序传入 # You can define functions that take a variable number of # positional arguments # 你可以定义一个函数,并让它接受可变数量的定位参数。 def varargs(*args): return args varargs(1, 2, 3) #=> (1,2,3) # You can define functions that take a variable number of # keyword arguments, as well # 你也可以定义一个函数,并让它接受可变数量的关键字参数。 def keyword_args(**kwargs): return kwargs # Let's call it to see what happens # 我们试着调用它,看看会发生什么: keyword_args(big="foot", loch="ness") #=> {"big": "foot", "loch": "ness"} # You can do both at once, if you like # 你还可以同时使用这两类参数,只要你愿意: def all_the_args(*args, **kwargs): print args print kwargs """ all_the_args(1, 2, a=3, b=4) prints: (1, 2) {"a": 3, "b": 4} """ # When calling functions, you can do the opposite of varargs/kwargs! # Use * to expand tuples and use ** to expand kwargs. # 在调用函数时,定位参数和关键字参数还可以反过来用。 # 使用 * 来展开元组,使用 ** 来展开关键字参数。 args = (1, 2, 3, 4) kwargs = {"a": 3, "b": 4} all_the_args(*args) # equivalent to foo(1, 2, 3, 4) # 相当于 all_the_args(1, 2, 3, 4) all_the_args(**kwargs) # equivalent to foo(a=3, b=4) # 相当于 all_the_args(a=3, b=4) all_the_args(*args, **kwargs) # equivalent to foo(1, 2, 3, 4, a=3, b=4) # 相当于 all_the_args(1, 2, 3, 4, a=3, b=4) # Python has first class functions # 函数在 Python 中是一等公民 def create_adder(x): def adder(y): return x + y return adder add_10 = create_adder(10) add_10(3) #=> 13 # There are also anonymous functions # 还有匿名函数 (lambda x: x > 2)(3) #=> True # There are built-in higher order functions # 还有一些内建的高阶函数 map(add_10, [1,2,3]) #=> [11, 12, 13] filter(lambda x: x > 5, [3, 4, 5, 6, 7]) #=> [6, 7] # We can use list comprehensions for nice maps and filters # 我们可以使用列表推导式来模拟 map 和 filter [add_10(i) for i in [1, 2, 3]] #=> [11, 12, 13] [x for x in [3, 4, 5, 6, 7] if x > 5] #=> [6, 7] #################################################### ## 5\. Classes ## 5\. 类 #################################################### # We subclass from object to get a class. # 我们可以从对象中继承,来得到一个类。 class Human(object): # A class attribute. It is shared by all instances of this class # 下面是一个类属性。它将被这个类的所有实例共享。 species = "H. sapiens" # Basic initializer # 基本的初始化函数(构造函数) def __init__(self, name): # Assign the argument to the instance's name attribute # 把参数赋值为实例的 name 属性 self.name = name # An instance method. All methods take self as the first argument # 下面是一个实例方法。所有方法都以 self 作为第一个参数。 def say(self, msg): return "%s: %s" % (self.name, msg) # A class method is shared among all instances # They are called with the calling class as the first argument # 类方法会被所有实例共享。 # 类方法在调用时,会将类本身作为第一个函数传入。 @classmethod def get_species(cls): return cls.species # A static method is called without a class or instance reference # 静态方法在调用时,不会传入类或实例的引用。 @staticmethod def grunt(): return "*grunt*" # Instantiate a class # 实例化一个类 i = Human(name="Ian") print i.say("hi") # prints out "Ian: hi" # 打印出 "Ian: hi" j = Human("Joel") print j.say("hello") # prints out "Joel: hello" # 打印出 "Joel: hello" # Call our class method # 调用我们的类方法 i.get_species() #=> "H. sapiens" # Change the shared attribute # 修改共享属性 Human.species = "H. neanderthalensis" i.get_species() #=> "H. neanderthalensis" j.get_species() #=> "H. neanderthalensis" # Call the static method # 调用静态方法 Human.grunt() #=> "*grunt*" #################################################### ## 6\. Modules ## 6\. 模块 #################################################### # You can import modules # 你可以导入模块 import math print math.sqrt(16) #=> 4 # You can get specific functions from a module # 也可以从一个模块中获取指定的函数 from math import ceil, floor print ceil(3.7) #=> 4.0 print floor(3.7) #=> 3.0 # You can import all functions from a module. # Warning: this is not recommended # 你可以从一个模块中导入所有函数 # 警告:不建议使用这种方式 from math import * # You can shorten module names # 你可以缩短模块的名称 import math as m math.sqrt(16) == m.sqrt(16) #=> True # Python modules are just ordinary python files. You # can write your own, and import them. The name of the # module is the same as the name of the file. # Python 模块就是普通的 Python 文件。 # 你可以编写你自己的模块,然后导入它们。 # 模块的名称与文件名相同。 # You can find out which functions and attributes # defines a module. # 你可以查出一个模块里有哪些函数和属性 import math dir(math)
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