Of course, we can use Python for more complicated tasks than adding two and two together. For instance, we can write an initial subsequence of the Fibonacci series as follows:
>>> # 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.
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.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: <
, >
, ==
, <=
, >=
and !=
.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:
>>> 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:
>>> 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.