Python从0开始--学习旅程3
一、Python控制流
1、Python if分支语句
if 单分支语法
if condition:
statement
statement
...
例子：
In [1]: count = int(raw_input('Plz enter your math record: '))
...: if count >= 80:
...: print 'Larger than eighty!'
...:
Plz enter your math record: 87
Larger than eighty!
if 双分支语法
if condition:
statement
statement
...
else:
statement
statement
...
例子
In [2]: count = int(raw_input('Plz enter your math record: '))
...: if count >= 80:
...: print 'Larger than eighty!'
...: else:
...: print 'Lower than eighty!'
...:
Plz enter your math record: 72
Lower than eighty!
In [3]: sex = raw_input('Plz tell me your gender: ')
...: if sex == 'male':
...: print 'Man'
...: else:
...: print 'Woman'
...:
Plz tell me your gender: female
Woman
if 多分支语法
if condition:
statement
statement
...
elif condition:
statement
statement
...
elif condition:
statement
statement
...
else:
statement
statement
...
例子
In [4]: count = int(raw_input('Plz enter your math record: '))
...: print count
...: if count < 60:
...: print 'Bad! Come on!'
...: elif count <= 80:
...: print 'Good! Plz study harder'
...: else:
...: print 'Best! You chaojibang'
...:
Plz enter your math record: 33
33
Bad! Come on!
In [5]: count = int(raw_input('Plz enter your math record: '))
...: print count
...: if count < 60:
...: print 'Bad! Come on!'
...: elif count <= 80:
...: print 'Good! Plz study harder'
...: else:
...: print 'Best! You chaojibang'
...:
Plz enter your math record: 89
89
Best! You chaojibang
二、Python 循环语句while
while循环的语法
i = 1
while condition:
statement1
statement2
...
i = i + 1
else:
statement1
statement2
...
这里的循环计数器i必须在循环体外附一个值，同时在循环体内也必须累加，实现循环。
例子：计算等差数列的和
In [6]: i = 1
...: x1 = 1
...: d = 3
...: s = 1
...: while i < 100:
...: x1 = x1 + d
...: s = s + x1
...: i = i + 1
...: print 'Sum of arithmetic progression: ', s
...:
Sum of arithmetic progression: 14950
三、Python 循环语句for
for target in sequences:
statements
sequences可以是列表（list）、元主（tuple）、字符串（srings）文件（files）。
例子
sequences为列表：
In [7]: ls = [1,2,3,'liu','shun','xiang',10,33.9]
...: for c in ls:
...: print c
...: else:
...: print 'End for'
...:
1
2
3
liu
shun
xiang
10
33.9
End for
sequences为元组
In [8]: tuple1 = (2,10,44,range(1,13,3))
In [9]: tuple1
Out[9]: (2, 10, 44, [1, 4, 7, 10])
In [10]: for f in tuple1:
...: print f
...:
2
10
44
[1, 4, 7, 10]
sequences为字符串
In [12]: s1 = 'Snake.Liu'
...: i = 1
...: for c in s1:
...: print format(i, '2.0f'), c
...: i = i + 1
...: else:
...: print 'Out for'
...:
1 S
2 n
3 a
4 k
5 e
6 .
7 L
8 i
9 u
Out for
二、Python自定义函数
自定义函数语法
def function_name(parameters):
statement1
statement2
statement3
...
有关自定义函数有以下几点说明：
1）参数parameters可有可无，有的话，函数运算时必须对应给出参数的值
2）无需括号将函数体括起来
3）函数名后面的冒号不可少，且换行后需缩进
例子：
In [13]: def test_a():
...: print 'Hello World'
...: print 'Liushuxniang'
...: print 'Start Programing'
...: test_a()
...: print 'End Programing'
...:
Start Programing
Hello World
Liushuxniang
End Programing
In [14]: def test_b(x,y):
...: import math
...: p = x + y
...: q = math.pow(x,2) + math.pow(y,3)
...: print 'x=',x
...: print 'y=',y
...: print 'p=',p
...: print 'q=',q
...:
In [15]: test_b(10,3)
x= 10
y= 3
p= 13
q= 127.0
有返回值的自定义函数
def function_name(parameters):
statement1
statement2
...
return value
例子：
In [16]: def my_function(x,y):
...: import math
...: z = float(format(math.log10(x) + math.log1p(y),'.2f'))
...: return x,y,z #或者return(x, y, z)
...:
...: x,y,z = my_function(10,2)
...: print x,y,z
...:
10 2 2.1
含默认参数值的函数
def function_name(parameter1,parameter2 = value, parameter3 = value):
statememt1
statement2
statememt3
...
In [17]: def test( x, y = 3, z = 10 ):
...: import math
...: p = math.pow(x,y) + y*z
...: q = 100*math.log(math.pow(x,y))/z
...: return p, float(format(q,'.2f'))
...:
...: p, q = test(10)
...:
In [18]: print p,q
1030.0 69.08
三、下期预告
第三方扩展库的安装和使用