Python语言实例开发代码分析

# 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  #=> 28  -  1  #=> 710  *  2  #=> 2035  /  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 float2.0 # 这是一个浮点数11.0  /  4.0  #=> 2.75 ahhh...much better11.0  /  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TrueFalse# negate with not# 使用 not 来取反not  True  #=> Falsenot  False  #=> True# Equality is ==# 等式判断用 ==1  ==  1  #=> True2  ==  1  #=> False# Inequality is !=# 不等式判断是用 !=1  !=  1  #=> False2  !=  1  #=> True# More comparisons# 还有更多的比较运算1  <  10  #=> True1  >  10  #=> False2  <=  2  #=> True2  >=  2  #=> True# Comparisons can be chained!# 居然可以把比较运算串连起来！1  <  2  <  3  #=> True2  <  3  <  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  #=> FalseNone  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]  #=> 1tup[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)  #=> 3tup  +  (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  #=> True1  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")  #=> 1filled_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)  #=> 1filled_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 5filled_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  #=> True10  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  <  10:    # This elif clause is optional. # 这里的 elif 子句是可选的    print  "some_var is smaller than 10."    # （译注：意为“some_var 比 10 小”。）else: # This is optional too.                # 这一句也是可选的    print  "some_var is indeed 10."    # （译注：意为“some_var 就是 10”。）"""For loops iterate over listsfor 循环可以遍历列表prints:如果要打印出：    dog is a mammal    cat is a mammal    mouse is a mammal"""for  animal in  ["dog",  "cat",  "mouse"]:    # You can use % to interpolate formatted strings    # 别忘了你可以使用 % 来格式化字符串    print  "%s is a mammal"  %  animal    # （译注：意为“%s 是哺乳动物”。）"""`range(number)` returns a list of numbersfrom zero to the given number`range(数字)` 会返回一个数字列表，这个列表将包含从零到给定的数字。prints:如果要打印出：    0    1    2    3"""for  i  in  range(4):    print  i"""While loops go until a condition is no longer met.while 循环会一直继续，直到条件不再满足。prints:如果要打印出：    0    1    2    3"""x  =  0while  x  <  4:    print  x    x  +=  1  # Shorthand for x = x + 1            # 这是 x = x + 1 的简写方式# Handle exceptions with a try/except block# 使用 try/except 代码块来处理异常# Works on Python 2.6 and up:# 适用于 Python 2.6 及以上版本：try:    # Use raise to raise an error    # 使用 raise 来抛出一个错误    raise  IndexError("This is an index error")    # 抛出一个索引错误：“这是一个索引错误”。except  IndexError  as  e:    pass    # Pass is just a no-op. Usually you would do recovery here.            # pass 只是一个空操作。通常你应该在这里做一些恢复工作。###################################################### 4. Functions## 4. 函数##################################################### Use def to create new functions# 使用 def 来创建新函数def  add(x,  y):    print  "x is %s and y is %s"  %  (x,  y)    # （译注：意为“x 是 %s 而且 y 是 %s”。）    return  x  +  y    # Return values with a return statement                    # 使用 return 语句来返回值# Calling functions with parameters# 调用函数并传入参数add(5,  6)  #=> 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  argsvarargs(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  adderadd_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  mathprint  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,  floorprint  ceil(3.7)  #=> 4.0print  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  mmath.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  mathdir(math)