3.2 开始编程 First Steps Towards Programming

Of course, we can use Python for more complicated tasks than adding two and two together. For instance, we can write an initial sub-sequence of the Fibonacci series as follows:

当然，我们可以用 Python 做比2加2更复杂的事。例如，我们可以用以下的方法输出菲波那契（Fibonacci）序列的子序列：

>>> # Fibonacci series:
... # the sum of two elements defines the next
... a, b = 0, 1
>>> while b < 10:
...       print b
...       a, b = b, a+b
...
1
1
2
3
5
8

This example introduces several new features.

示例中介绍了一些新功能：

The first line contains a multiple assignment: the variables a and b simultaneously get the new values 0 and 1. On the last line this is used again, demonstrating that the expressions on the right-hand side are all evaluated first before any of the assignments take place. The right-hand side expressions are evaluated from the left to the right.

第一行包括了复合参数：变量 a 和 b 同时被赋值为0和1。最后一行又一次使用了这种技术，证明了在赋值之前表达式右边先进行了运算。右边的表达式从左到右运算。

The while loop executes as long as the condition (here: b < 10) remains true. In Python, like in C, any non-zero integer value is true; zero is false. The condition may also be a string or list value, in fact any sequence; anything with a non-zero length is true, empty sequences are false. The test used in the example is a simple comparison. The standard comparison operators are written the same as in C: < (less than), > (greater than), == (equal to), <= (less than or equal to), >= (greater than or equal to) and != (not equal to).

while 循环运行在条件为真时执行。在 Python 中，类似于 C 任何非零值为真，零为假。这个条件也可以用于字符串或链表，事实上于对任何序列类型，长度非零时为真，空序列为假。示例所用的是一个简单的比较。标准的比较运算符写法和 C 相同： < （小于），> （大于），== （等于），<= （小于等于），>=（大于等于）和!= （不等于）。

The body of the loop is indented: indentation is Python's way of grouping statements. Python does not (yet!) provide an intelligent input line editing facility, so you have to type a tab or space(s) for each indented line. In practice you will prepare more complicated input for Python with a text editor; most text editors have an auto-indent facility. When a compound statement is entered interactively, it must be followed by a blank line to indicate completion (since the parser cannot guess when you have typed the last line). Note that each line within a basic block must be indented by the same amount.

循环体是缩进的：缩进是 Python 对语句分组的方法。 Python 还没有提供一个智能编辑功能，你要在每一个缩进行输入一个 tab 或（一个或多个）空格。实际上你可能会准备更为复杂的文本编辑器来编写你的 Python 程序，大多数文本编辑器都提供了自动缩进功能。交互式的输入一个复杂语句时，需要用一个空行表示完成（因为解释器没办法猜出你什么时候输入最后一行）。需要注意的是每一行都要有相同的缩进来标识这是同一个语句块。

The print statement writes the value of the expression(s) it is given. It differs from just writing the expression you want to write (as we did earlier in the calculator examples) in the way it handles multiple expressions and strings. Strings are printed without quotes, and a space is inserted between items, so you can format things nicely, like this:

print 语句打印给定表达式的值。它与你仅仅输入你需要的表达式（就像前面的计算器示例）不同，它可以同时输出多个表达式。字符串输出时没有引号，各项之间用一个空格分开，你可以很容易区分它们，如下所示：

>>> i = 256*256
>>> print 'The value of i is', i
The value of i is 65536

A trailing comma avoids the newline after the output:

print 语句末尾的逗号避免了输出中的换行：

>>> a, b = 0, 1
>>> while b < 1000:
...     print b,
...     a, b = b, a+b
...
1 1 2 3 5 8 13 21 34 55 89 144 233 377 610 987

Note that the interpreter inserts a newline before it prints the next prompt if the last line was not completed.

需要注意的是，如果最后一行仍没有写完，解释器会在它打印下一个命令时插入一个新行。