Python语法(一)

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1.两种解释器

CPython由C写成；

Jython由Java写成，特点包括

         只要有 Java 虚拟机，就能运行Jython
         拥有访问 Java 包与类库的能力
         为 Java 开发环境提供了脚本引擎
         能够很容易的测试 Java 类库
         提供访问 Java 原生异常处理的能力
        继承了 JavaBeans 特性和内省能力
        鼓励 Python 到Java 的开发（反之亦然）
         GUI 开发人员可以访问 Java 的 AWT/Swing 库
        利用了 Java 原生垃圾收集器（CPython 未实现此功能）

2.交互式解释器

>>> primary prompt:expecting the next Python statement

...secondary prompt:indicates that the interpreter is waiting for additional input to complete the current statement

主提示符下，'''表示要输入多行

次提示符下，输入if statement 回车后，缩进然后输入执行语句最后空行回车表示输入完成

3.print用法

>>>print variable #输出 variable content

>>>variables #输出 'variable content'

>>>_ #last evaluated expression

    logfile = open('/tmp/mylog.txt', 'a')
    print >> logfile, 'Fatal error: invalid input!' #redirect output to file named logfile
    logfile.close()

    >>> user = raw_input('Enter login name: ')#built-in function to obtain user input from command line
    Enter login name: root
    >>> print 'Your login is:', user
    Your login is: root    # comma seperate two variables

>>>print"%s words %d" %("python",10)

循环中，print item会为每一个item添加换行符，而print item, 则会用空格代替换行

4.Lists and Tuples

lists and tuples can store different types of objects.

Lists are enclosed in brackets ( [ ] ) and their elements and size can be changed. Tuples are
enclosed in parentheses ( ( ) ) and cannot be updated (although their contents may be). Tuples can be thought of for now as “read-only” lists.

>>> aList = [1, 2, 3, 4]
>>> aList
[1, 2, 3, 4]
>>> aList[0]
1
>>> aList[2:]
[3, 4]
>>> aList[:3]
[1, 2, 3]
>>> aList[1] = 5
>>> aList
[1, 5, 3, 4]
Slice access to a tuple is similar, except it cannot be modified:
>>> aTuple = ('robots', 77, 93, 'try')
>>> aTuple
('robots', 77, 93, 'try')
>>> aTuple[:3]
('robots', 77, 93)
>>> aTuple[1] = 5
Traceback (innermost last):
File "<stdin>", line 1, in ?
TypeError: object doesn't support item assignment

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