5.1变量和表达式
例子5.1复利计算机（Simple Compound -Interest Calculation）
按照数字(int)类型输出:
<span style="font-size:18px;">import string
principal=1000 #Initial amount
rate =0.05 #Interest rate
numyears=5 #Number of years
year =1
while year <= numyears:
principal=principal*(1+rate)
print year ,principal
year+=1</span><span style="font-size:18px;">import string
principal=1000 #Initial amount
rate =0.05 #Interest rate
numyears=5 #Number of years
year =1
while year <= numyears:
principal=principal*(1+rate)
print str(year) +" " +str(principal)
year+=1</span>输出结果：<span style="font-size:18px;">1 1050.0 2 1102.5 3 1157.625 4 1215.50625 5 1276.2815625</span>Python语言的动态特性。最初，它被赋值给principal，当赋值动作发生改变的时候，principal最初的绑定值1000被丢弃。赋值结束，不但principal绑定的值发生了变化，它的类型也随着赋值动作发生了相应的变化。在本例子中，由于rate是一个浮点数，principal最终也是一个浮点数。
Python中每个语句以换行结束，当然你也可以在一行中写多个语句，但是各个语句之间要用分号分隔。
principal=1000；rate=0.05; numyears=5；
为了有一个更好的输出格式，可以用格式控制符：
<span style="font-size:18px;">print "%3d %0.2f" %(year,principal)</span>其中：%3d是将一个整数在宽度在宽度为3个字符的栏中右对齐，%0.2f 是将一个浮点数的小数点后部分转换为2位。
5.2 条件语句
<span style="font-size:18px;">a=10;b=60;
if a<b:
z=b
else:
z=a
print z</span>可以通过or,and 和not关键字建立任意的条件表达式：<span style="font-size:18px;">c=100
if a<=b and b<=c:
print "b is between a and c"
if not(b<a or b>c):
print "b is still btween a and c"</span>用elif语句可以检验多重条件（可以用来代替其它语言中的switch语句）<span style="font-size:18px;">a='+'
print a
if a=='+':
op='PLUS'
elif a=='-':
op='MINUS'
elif a=='*':
op='MULTLPLY'
else:
raise RuntimeError,"Unknown operator"
print op</span>5.3字符串
字符串是一个以0开始，整数索引的字符序列，要获得字符串s中的第i+1个字符，可以使用索引操作符s[i]:
<span style="font-size:18px;">a='Hello world' d=a[1] print d</span>
<span style="font-size:18px;">a='Hello world' c=a[0:5] d=a[6:] e=a[3:8] print a print c print d print e </span>连接字符串:可以使用(+)
<span style="font-size:18px;">num = "1" # string type num = "Let's go" # string type num = "He's \"old\"" # string type mail = """China: hello I am you! """ # special string format print mail string = 'xiaoyi' # get value by index copy = string[0] + string[1] + string[2:6] # note: [2:6] means [2 5] or[2 6) print copy = string[:4] # start from 1 copy = string[2:] # to end copy = string[::1] # step is 1, from start to end copy = string[::2] # step is 2 copy = string[-1] # means 'i', the last one copy = string[-4:-2:-1] # means 'yoa', -1 step controls direction </span>5.4 列表和元组(Lists & Tuples)
例如：names=["zhang","wang","li","zhao"]
<span style="font-size:18px;">#列表
names=["zhang","wang","li","zhao"]
a=names[0]
names[0]="fu"
# len()函数用来得到列表的长度
print len(names)
#append() 在末尾添加新的元素
names.append("pan")
#insert(index,aMember)把元素插入的index之前的位置
names.insert(2,"zhou")
print names
#b返回 下标为0 1的值
b=names[0:2]
c=names[2:]
#利用（+）运算符连接列表
str1=[1,2,3]+[4,5]
print "+连接符"
print str1
#列表元素可以是任意的 python对象
str2=[1,"zjgs",3.14,["Mark",7,9,[100,101]],10]
print str2
print str2[1]
print str2[3][2]
print str2[3][3][1]
</span><span style="font-size:18px;">4 ['fu', 'wang', 'zhou', 'li', 'zhao', 'pan'] +连接符 [1, 2, 3, 4, 5] [1, 'zjgs', 3.14, ['Mark', 7, 9, [100, 101]], 10] zjgs 9 101</span>
元组例子：
<span style="font-size:18px;">print "元组系列" tup=(1,4,5,-9,10) tup2=(7,) #添加一个额外的逗号 first_name="wang" last_name="gang" phone=123456789 person=(first_name,last_name,phone) print tup print tup2 print person</span>
<span style="font-size:18px;">#range(i,j)函数建立一个整数序列，从i开始到j为止（包括i，但是不包括j）
#若第一个被省略，则默认0，还可以有第三个参数，步进值
for i in range(1,10):
print "2 to the %d power is %d" %(i,2**i)
a=range(5)
print a
b=range(1,8)
print b
c=range(0,14,3)#步长为3
print c
stra="Hello world"
for strc in stra:
print strc
strd=["kjksjf","iuiukj","zjgs"]
# print the number of a list
for name in strd:
print name</span>2 to the 1 power is 2 2 to the 2 power is 4 2 to the 3 power is 8 2 to the 4 power is 16 2 to the 5 power is 32 2 to the 6 power is 64 2 to the 7 power is 128 2 to the 8 power is 256 2 to the 9 power is 512 [0, 1, 2, 3, 4] [1, 2, 3, 4, 5, 6, 7] [0, 3, 6, 9, 12] H e l l o w o r l d kjksjf iuiukj zjgs
原文地址：http://blog.csdn.net/u013476464/article/details/36408657
