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「译」 分分钟学会一门语言之 Python 篇

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声明:原文版权属于 Louie Dinh,原文以 CC BY-SA 3.0 协议发布。

Python was created by Guido Van Rossum in the early 90's. It is now one of the most popular languages in existence. I fell in love with Python for its syntactic clarity. It's basically executable pseudocode.

Python 是 90 年代初由 Guido Van Rossum 创立的。它是当前最流行的程序语言之一。它那纯净的语法令我一见倾心,它简直就是可以运行的伪码。

Feedback would be highly appreciated! You can reach me at @louiedinh or louiedinh [at] [google's email service]

非常欢迎您提交反馈!您可以通过 @louiedinh 联系到我,也可以发邮件到 louiedinh 开头的 Google Email 账号。

Note: This article applies to Python 2.7 specifically, but should be applicable to Python 2.x. Look for another tour of Python 3 soon!

请注意:本文以 Python 2.7 为基准,但也应该适用于所有 2.X 版本。还要继续学习最新的 Python 3 哦!

# 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 evaluate to False.# All other values are True# None、0 以及空字符串和空列表都等于 False,# 除此以外的所有值都等于 True。0 == False #=> True"" == False #=> True###################################################### 2. Variables and Collections## 2. 变量和集合##################################################### Printing is pretty easy# 打印输出很简单print "I'm Python. Nice to meet you!"# No need to declare variables before assigning to them.# 在赋值给变量之前不需要声明some_var = 5 # Convention is to use lower_case_with_underscores # 变量名的约定是使用下划线分隔的小写单词some_var #=> 5# Accessing a previously unassigned variable is an exception.# See Control Flow to learn more about exception handling.# 访问一个未赋值的变量会产生一个异常。# 进一步了解异常处理,可参见下一节《控制流》。some_other_var # Raises a name error # 会抛出一个名称错误# if can be used as an expression# if 可以作为表达式来使用"yahoo!" if 3 > 2 else 2 #=> "yahoo!"# Lists store sequences# 列表用于存储序列li = []# You can start with a prefilled list# 我们先尝试一个预先填充好的列表other_li = [4, 5, 6]# Add stuff to the end of a list with append# 使用 append 方法把元素添加到列表的尾部li.append(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 numbers from 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)

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译者后记

哗众取宠?

此文一发,估计又会被喷:“分分钟学会?哗众取宠!Python 哪有那么简单!!!”

原文取自一个很有意思的网站 Learn X in Y minutes(分分钟学会一门语言),我确实被这个口号吸引住了;然后凭着对 Python 的好奇,拿来翻译。为了更准确地翻译出原文的用意,我自己还特意学习了这篇 中文版的 Python 基础教程。(当然,如果你发现了错误,请立即留言纠正,多谢!)

所以你看,一篇“哗众取宠”的文章本身不是坏事,只要它能勾起好奇、激发兴趣,为读者打开一扇门、展现一个新的世界,就已经功德圆满。

或许真的有人从这篇文章开始走进了 Python 的世界,然后改变了自己的人生、改变了整个世界?谁知道呢,反正我自己会一直翻译、一直传播、一直哗众取宠下去就是了。

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