标签：python2.7自学笔记1——使用python作为计算器
1、number
数字可以直接在python运算，使用圆括号分组
In [1]: 2+2 Out[1]: 4 In [2]: 50-5*6 Out[2]: 20 In [3]: (50-5.0*6)/4 Out[3]: 5.0 In [4]: 8/5.0 Out[4]: 1.6
在进行除法/的时候，如果2个除数都是int型，则返回的值也为整型int：
如果有1个除数为浮点型float，则结果值为浮点型float；
使用运算符//做除法，则返回的值为除后取整
使用%做除法取余数；
In [5]: 17/3 Out[5]: 5 In [6]: 17/3.0 Out[6]: 5.666666666666667 In [7]: 17//3.0 Out[7]: 5.0 In [8]: 17%3 Out[8]: 2
使用**来计算乘方：
In [9]: 5**2 Out[9]: 25 In [10]: 2**7 Out[10]: 128
使用=号赋值：
In [11]: width=20 In [12]: height=5*9 In [13]: width * height Out[13]: 900
如果一个变量没有定义，那么直接使用它会出错：
In [14]: n --------------------------------------------------------------------------- NameError Traceback (most recent call last) <ipython-input-14-fe13119fb084> in <module>() ----> 1 n NameError: name ‘n‘ is not defined
整型和浮点类型的转换：
In [15]: 3*3.75/1.5 Out[15]: 7.5 In [16]: 7.0/2 Out[16]: 3.5
可以将最后打印的计算结果直接给“_”符号
In [17]: tax=12.5/100 In [18]: price=100.50 In [19]: tax * price Out[19]: 12.5625 In [20]: price+_ Out[20]: 113.0625 In [21]: round(_,2) Out[21]: 113.06
2、String
可以使用单引号‘‘和双引号来直接引用String,反斜杠可以转义引号：
In [22]: ‘spam eggs‘ Out[22]: ‘spam eggs‘ In [23]: ‘doesn\‘t‘ Out[23]: "doesn‘t" In [24]: "doesn‘t" Out[24]: "doesn‘t" In [25]: ‘"Yes," he said.‘ Out[25]: ‘"Yes," he said.‘ In [26]: "\"Yes,\" he said." Out[26]: ‘"Yes," he said.‘ In [27]: ‘"Isn\‘t," she said.‘ Out[27]: ‘"Isn\‘t," she said.‘
使用print命令可以忽略字符引号，并且可以打印特殊意义符号：
In [28]: ‘"Isn\‘t," she said.‘ Out[28]: ‘"Isn\‘t," she said.‘ In [29]: print ‘"Isn\‘t," she said.‘ "Isn‘t," she said. In [30]: s = ‘First line.\nSecond line.‘ In [31]: s Out[31]: ‘First line.\nSecond line.‘ In [32]: print s First line. Second line.
如果不想打印特殊字符，可以在第一个引号前面加r：
In [33]: print ‘C:\some\name‘ C:\some ame In [34]: print r‘C\some\name‘ C\some\name
使用三元引号可以将多行放在一行里面，但在第一个引号后面加\符号则还是会使用多行模式：
In [38]: print """ ....: Usage: thingy [OPTIONS] ....: -h Display this usage message ....: -H hostname Hostname to connect to ....: """ Usage: thingy [OPTIONS] -h Display this usage message -H hostname Hostname to connect to
String可以使用+号连接或者*号运算
In [40]: 3 * ‘un‘ + ‘ium‘ Out[40]: ‘unununium‘
连接多个字符串可以使用以下方式：
In [42]: ‘Py‘ ‘thon‘ Out[42]: ‘Python‘
使用+符号可以将变量与字符串相连接：
In [43]: prefix = ‘Py‘ In [44]: prefix + ‘thon‘ Out[44]: ‘Python‘
当需要将比较长的字符串连接在一起的时候，使用引号的方式比较有用：
In [45]: text = (‘Put several strings within parentheses ‘ ....: ‘to have them joined together.‘) In [46]: text Out[46]: ‘Put several strings within parentheses to have them joined together.‘
字符串可以有索引：
In [47]: word = ‘Python‘ In [48]: word[0] Out[48]: ‘P‘ In [49]: word[5] Out[49]: ‘n‘ In [50]: word[-1] Out[50]: ‘n‘ In [51]: word[-2] Out[51]: ‘o‘ In [52]: word[-6] Out[52]: ‘P‘
字符串的切片：
In [53]: word[0:2] Out[53]: ‘Py‘ In [54]: word[2:5] Out[54]: ‘tho‘ In [55]: word[:2] + word[2:] Out[55]: ‘Python‘ In [56]: word[:4] + word[4:] Out[56]: ‘Python‘
字符串切片索引示意：
+---+---+---+---+---+---+ | P | y | t | h | o | n | +---+---+---+---+---+---+ 0 1 2 3 4 5 6 -6 -5 -4 -3 -2 -1
超过索引顺序的切片可以比较友好的处理：
In [68]: word[4:42] Out[68]: ‘on‘ In [69]: word[42:]
String不能被改变：
In [69]: word[0] = ‘J‘ --------------------------------------------------------------------------- TypeError Traceback (most recent call last) <ipython-input-69-197b67ffdd83> in <module>() ----> 1 word[0] = ‘J‘ TypeError: ‘str‘ object does not support item assignment
如果需要不同的字符串，可以生成新的字符串：
In [70]: ‘J‘ + word[1:] Out[70]: ‘Jython‘ In [71]: word[:2] + ‘py‘ Out[71]: ‘Pypy‘
使用内置的len函数可以计算字符串的长度：
In [72]: len(word) Out[72]: 6
本文出自 “平凡之路” 博客，请务必保留此出处http://linjohn.blog.51cto.com/1026193/1608530
标签：python2.7自学笔记1——使用python作为计算器
原文地址：http://linjohn.blog.51cto.com/1026193/1608530
