老程序员通过一篇文章快速学会python这门新语言

谁践踏了优雅 2022-07-15 05:29 184阅读 0赞

老程序员快速掌握一门新的语言，如果还是逐个看语法手册，太费时间了，通过一篇文章，无需太多解析，自己就可以看个大概了。接下来看看标准库，然后就可以开始干活了。
    
    先来看一个简单的任务：
    简单测试局域网中的电脑是否连通.这些电脑的ip范围从192.168.0.101到192.168.0.200.   
    import subprocess
    
    cmd="cmd.exe"
    begin=101
    end=200
    while begin<end:
    
        p=subprocess.Popen(cmd,shell=True,stdout=subprocess.PIPE,
                       stdin=subprocess.PIPE,
                       stderr=subprocess.PIPE)
        p.stdin.write("ping 192.168.1."+str(begin)+"\n")
    
        p.stdin.close()
        p.wait()
    
        print "execution result: %s"%p.stdout.read()
    
    这个程序保存之后可以直接运行.
    
    
    2 快速入门
    2.1 Hello world
        安装完Python之后,打开IDLE(Python GUI) , 该程序是Python语言解释器,你写的语句能够立即运行.我们写下一句著名的程序语句:
    
    print "Hello,world!"
    
        并按回车.你就能看到这句被K&R引入到程序世界的名言.
    
        在解释器中选择"File"--"New Window" 或快捷键 Ctrl+N , 打开一个新的编辑器.写下如下语句:
    
    print "Hello,world!"
    raw_input("Press enter key to close this window");
    
        保存为a.py文件.按F5,你就可以看到程序的运行结果了.这是Python的第二种运行方式.
    
        找到你保存的a.py文件,双击.也可以看到程序结果.Python的程序能够直接运行.
    
    2.2 国际化支持
        我们换一种方式来问候世界.新建一个编辑器并写如下代码:
    
    print "欢迎来到奥运中国!"
    raw_input("Press enter key to close this window");
    
        在你保存代码的时候,Python会提示你是否改变文件的字符集,结果如下:
    
    # -*- coding: cp936 -*- 
    
    print "欢迎来到奥运中国!"
    raw_input("Press enter key to close this window");
    
        将该字符集改为我们更熟悉的形式:
    
    # -*- coding: GBK -*- 
    
    print "欢迎来到奥运中国!" # 使用中文的例子
    raw_input("Press enter key to close this window");
    
        程序一样运行良好.
    2.3 方便易用的计算器
        用微软附带的计算器来计数实在太麻烦了.打开Python解释器,直接进行计算:
    
    a=100.0
    b=201.1
    c=2343
    print (a+b+c)/c
    
    2.4 字符串,ASCII和UNICODE
    
        可以如下打印出预定义输出格式的字符串:
    
    print """
    Usage: thingy [OPTIONS]
         -h                        Display this usage message
         -H hostname               Hostname to connect to
    """
    
        字符串是怎么访问的?请看这个例子:
    
    word="abcdefg"
    a=word[2]
    print "a is: "+a
    b=word[1:3]
    print "b is: "+b # index 1 and 2 elements of word.
    c=word[:2]
    print "c is: "+c # index 0 and 1 elements of word.
    d=word[0:]
    print "d is: "+d # All elements of word.
    e=word[:2]+word[2:]
    print "e is: "+e # All elements of word.
    f=word[-1]
    print "f is: "+f # The last elements of word.
    g=word[-4:-2]
    print "g is: "+g # index 3 and 4 elements of word.
    h=word[-2:]
    print "h is: "+h # The last two elements.
    i=word[:-2]
    print "i is: "+i # Everything except the last two characters
    l=len(word)
    print "Length of word is: "+ str(l)
    
        请注意ASCII和UNICODE字符串的区别:
    
    print "Input your Chinese name:"
    s=raw_input("Press enter to be continued");
    print "Your name is  : " +s;
    l=len(s)
    print "Length of your Chinese name in asc codes is:"+str(l);
    a=unicode(s,"GBK")
    l=len(a)
    print "I'm sorry we should use unicode char!Characters number of your Chinese \
    name in unicode is:"+str(l);
    
    2.5 使用List
        类似Java里的List,这是一种方便易用的数据类型:
    
    word=['a','b','c','d','e','f','g']
    a=word[2]
    print "a is: "+a
    b=word[1:3]
    print "b is: "
    print b # index 1 and 2 elements of word.
    c=word[:2]
    print "c is: "
    print c # index 0 and 1 elements of word.
    d=word[0:]
    print "d is: "
    print d # All elements of word.
    e=word[:2]+word[2:]
    print "e is: "
    print e # All elements of word.
    f=word[-1]
    print "f is: "
    print f # The last elements of word.
    g=word[-4:-2]
    print "g is: "
    print g # index 3 and 4 elements of word.
    h=word[-2:]
    print "h is: "
    print h # The last two elements.
    i=word[:-2]
    print "i is: "
    print i # Everything except the last two characters
    l=len(word)
    print "Length of word is: "+ str(l)
    print "Adds new element"
    word.append('h')
    print word
    
    2.6 条件和循环语句
    # Multi-way decision
    x=int(raw_input("Please enter an integer:"))
    if x<0:
        x=0
        print "Negative changed to zero"
    
    elif x==0:
        print "Zero"
    
    else:
        print "More"
    
    
    # Loops List
    a = ['cat', 'window', 'defenestrate']
    for x in a:
        print x, len(x)
    
    2.7 如何定义函数
    # Define and invoke function.
    def sum(a,b):
        return a+b
    
    
    func = sum
    r = func(5,6)
    print r
    
    # Defines function with default argument
    def add(a,b=2):
        return a+b
    r=add(1)
    print r
    r=add(1,5)
    print r
    
        并且,介绍一个方便好用的函数:
    
    # The range() function
    a =range(5,10)
    print a
    a = range(-2,-7)
    print a
    a = range(-7,-2)
    print a
    a = range(-2,-11,-3) # The 3rd parameter stands for step
    print a
    
    2.8 文件I/O
    spath="D:/download/baa.txt"
    f=open(spath,"w") # Opens file for writing.Creates this file doesn't exist.
    f.write("First line 1.\n")
    f.writelines("First line 2.")
    
    f.close()
    
    f=open(spath,"r") # Opens file for reading
    
    for line in f:
        print line
    
    f.close()
    
    2.9 异常处理
    
    s=raw_input("Input your age:")
    if s =="":
        raise Exception("Input must no be empty.")
    
    try:
        i=int(s)
    except ValueError:
        print "Could not convert data to an integer."
    except:
        print "Unknown exception!"
    else: # It is useful for code that must be executed if the try clause does not raise an exception
        print "You are %d" % i," years old"
    finally: # Clean up action
        print "Goodbye!"
    
    
    2.10 类和继承
    class Base:
        def __init__(self):
            self.data = []
        def add(self, x):
            self.data.append(x)
        def addtwice(self, x):
            self.add(x)
            self.add(x)
    
    # Child extends Base
    class Child(Base):
        def plus(self,a,b):
            return a+b
    
    oChild =Child()
    oChild.add("str1")
    print oChild.data
    print oChild.plus(2,3)
    
    
    2.11 包机制
        每一个.py文件称为一个module,module之间可以互相导入.请参看以下例子:
    # a.py
    def add_func(a,b):
        return a+b
    
    # b.py
    from a import add_func # Also can be : import a
    
    print "Import add_func from module a"
    print "Result of 1 plus 2 is: "
    print add_func(1,2)    # If using "import a" , then here should be "a.add_func"
    
    
        module可以定义在包里面.Python定义包的方式稍微有点古怪,假设我们有一个parent文件夹,该文件夹有一个child子文件夹.child中有一个module a.py . 如何让Python知道这个文件层次结构?很简单,每个目录都放一个名为_init_.py 的文件.该文件内容可以为空.这个层次结构如下所示: 
    parent 
      --__init_.py
      --child
        -- __init_.py
        --a.py
    
    b.py
    
        那么Python如何找到我们定义的module?在标准包sys中,path属性记录了Python的包路径.你可以将之打印出来:
    
    import sys
    
    print sys.path
    
        通常我们可以将module的包路径放到环境变量PYTHONPATH中,该环境变量会自动添加到sys.path属性.另一种方便的方法是编程中直接指定我们的module路径到sys.path 中:
    
    import sys
    sys.path.append('D:\\download')
    
    from parent.child.a import add_func
    
    
    print sys.path
    
    print "Import add_func from module a"
    print "Result of 1 plus 2 is: "
    print add_func(1,2)