Python学习入门基础教程(learning Python)--3.2 if-else分支语句 .

if-else分支语句结构的特点是当conditon条件满足时，执行if下的语句块，当condition条件不满足时执行else下的语句块，也就是说根据条件来控制让某些语句执行，某些语句不被执行。

if-else语法结构如下：
[python]view plaincopyprint?if conditon：

(tab) statement1

(tab) statement2

(tab) statement3

etc.

else：

(tab) statement1

(tab) statement2

(tab) statement3

etc.

if conditon：
(tab) statement1
(tab) statement2
(tab) statement3
etc.
else：
(tab) statement1
(tab) statement2
(tab) statement3
etc.

需要注意的是(a)在if的condition之后要有冒号'：'，else后边也要有一个冒号':',(2)if和else其下的每条语句都要用TAB键缩进。if-else条件控制分支语句的逻辑流程图如下图所示。



接下来沿用上节的例子，使用以下Python的if-else结构进行程序设计。

[python]view plaincopyprint?def input_info():

mat = int(raw_input("plz input your mathtic record: "))

eng = int(raw_input("plz input your english record: "))

his = int(raw_input("plz input your history record: "))

process_info(mat, eng, his)

def process_info(m, e, h):

ave = (m + e + h) / 3

if ave > 90:

print("Congratulation! ave = ", ave)

else:

print("Need improve! ave = ", ave)

def main():

input_info()

main()

def input_info():
mat = int(raw_input("plz input your mathtic record: "))
eng = int(raw_input("plz input your english record: "))
his = int(raw_input("plz input your history record: "))
process_info(mat, eng, his)

def process_info(m, e, h):
ave = (m + e + h) / 3
if ave > 90:
print("Congratulation! ave = ", ave)
else:
print("Need improve! ave = ", ave)

def main():
input_info()

main()

程序的运行结果如下图所示。