python基础篇第二篇

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一、数据运算

  举个例子一目了然就明白什么是运算符了;例子10+20=30,其中10,20为操作符 ,“+” 称为运算符。

python支持支持的类型运算符有:算术运算、比较(关系)运算符、赋值运算符、逻辑运算符、位运算符、成员运算符、身份运算符、运算符优先级,下面我们一个个来看。

 

1、算数运算:

假设变量a=10,变量b=20:

运算符描述实例
+ 加 - 两个对象相加 a + b 输出结果 30
- 减 - 得到负数或是一个数减去另一个数 a - b 输出结果 -10
* 乘 - 两个数相乘或是返回一个被重复若干次的字符串 a * b 输出结果 200
/ 除 - x除以y b / a 输出结果 2
% 取模 - 返回除法的余数 b % a 输出结果 0
** 幂 - 返回x的y次幂 a**b 为10的20次方, 输出结果 100000000000000000000
// 取整除 - 返回商的整数部分 9//2 输出结果 4 , 9.0//2.0 输出结果 4.0



 

 

 

 

 

 

练习实例:

 1 #!/usr/bin/env python
 2 # -*- coding :utf-8 -*-
 3 
 4 a = 10
 5 b = 20
 6 
 7 c = a + b   #两数相加
 8 print(c)
 9 
10 c = a - b   #两数相减
11 print(c)
12 
13 c = a * b   #两数相乘
14 print(c)
15 
16 c = a / b   #两数相除
17 print(c)
18 
19 c = a % b   #取模,返回除法的余数
20 print(c)
21 
22 c = a ** b  #幂(次方)
23 print(c)
24 
25 c = a // b  #取整数,返回商的整数部分
26 print(c)

 

以上练习实例执行结果

 1 C:\\Python\\Python35\\python.exe E:/Python课程/s13/day2/运算符.py
 2 30
 3 -10
 4 200
 5 0.5
 6 10
 7 100000000000000000000
 8 0
 9 
10 Process finished with exit code 0

 

2、比较运算符:

运算符描述实例
== 等于 - 比较对象是否相等 (a == b) 返回 False。 
!= 不等于 - 比较两个对象是否不相等 (a != b) 返回 true. 
<> 不等于 - 比较两个对象是否不相等(一般都用!=,在python3中已被移除) (a <> b) 返回 true。这个运算符类似 != 。
> 大于 - 返回x是否大于y (a > b) 返回 False。
< 小于 - 返回x是否小于y。所有比较运算符返回1表示真,返回0表示假。这分别与特殊的变量True和False等价。注意,这些变量名的大写。 (a < b) 返回 true。 
>= 大于等于 - 返回x是否大于等于y。 (a >= b) 返回 False。
<= 小于等于 - 返回x是否小于等于y。 (a <= b) 返回 true。 

 

实例练习:

 1 a=66
 2 b=88
 3 c=0
 4 
 5 a = 10
 6 b = 20
 7 8 
 9 if (a == b):        #等于
10     print(a等于b)
11 else:
12     print(a不等于b)
13 
14 if (a != b):        #不等于
15     print(a不等于b)
16 else:
17     print(a等于b)
18 
19 # if (a <> b):        #不等于(python2.x)
20 #     print(‘a不等于b‘)
21 # else:
22 #     print(‘a等于b‘)
23 
24 
25 if (a < b):         #小于
26     print(a小于b)
27 else:
28     print(a不小于b)
29 
30 if (a > b):         #大于
31     print(a大于b)
32 else:
33     print(a不大于b )
34 
35 
36 if (a <= b):        #小于等于
37     print(a小于等于b)
38 else:
39     print(不对)
40     
41 if (a >= b):        #大于等于
42     print(a大于等于b)
43 else:
44     print(不对)

以上实例执行结果:

C:\\Python\\Python35\\python.exe E:/Python课程/s13/day2/运算符.py
错误
a不等于b
错误
a小于b
错误
a小于等于b

Process finished with exit code 0

 

3、赋值运算符:

运算符描述实例
= 简单的赋值运算符 c = a + b 将 a + b 的运算结果赋值为 c
+= 加法赋值运算符 c += a 等效于 c = c + a
-= 减法赋值运算符 c -= a 等效于 c = c - a
*= 乘法赋值运算符 c *= a 等效于 c = c * a
/= 除法赋值运算符 c /= a 等效于 c = c / a
%= 取模赋值运算符 c %= a 等效于 c = c % a
**= 幂赋值运算符 c **= a 等效于 c = c ** a
//= 取整除赋值运算符 c //= a 等效于 c = c // a

 

 

 

 

 

 

 

 

实例练习:

 1 a = 2
 2 b = 3
 3 c = 0
 4 
 5 c = a + b       #把a+b的变量和赋值给c变量
 6 print(c)
 7 
 8 c += a          #意思是c = c + a
 9 print(c)
10 
11 c -= a          #意思是c = c - a
12 print(c)
13 
14 c *= a          #意思是c = c * a
15 print(c)
16 
17 c /= a          #意思是c = c / a
18 print(c)
19 
20 c %= a          #意思是c = c % a
21 print(c)
22 
23 c **= a         #意思是c = c ** a
24 print(c)
25 
26 c //= a         #意思是c = c // a
27 print(c)

以上实例执行结果:

 1 C:\\Python\\Python35\\python.exe E:/Python课程/s13/day2/运算符.py
 2 5
 3 7
 4 5
 5 10
 6 5.0
 7 1.0
 8 1.0
 9 0.0
10 
11 Process finished with exit code 0

 

4、位运算符:

执行二进制运算

运算符描述实例
& 按位与运算符:参与运算的两个值,如果两个相应位都为1,则该位的结果为1,否则为0 (a & b) 输出结果 12 ,二进制解释: 0000 1100
| 按位或运算符:只要对应的二个二进位有一个为1时,结果位就为1。 (a | b) 输出结果 61 ,二进制解释: 0011 1101
^ 按位异或运算符:当两对应的二进位相异时,结果为1  (a ^ b) 输出结果 49 ,二进制解释: 0011 0001
~ 按位取反运算符:对数据的每个二进制位取反,即把1变为0,把0变为1  (~a ) 输出结果 -61 ,二进制解释: 1100 0011, 在一个有符号二进制数的补码形式。
<< 左移动运算符:运算数的各二进位全部左移若干位,由"<<"右边的数指定移动的位数,高位丢弃,低位补0。 a << 2 输出结果 240 ,二进制解释: 1111 0000
>> 右移动运算符:把">>"左边的运算数的各二进位全部右移若干位,">>"右边的数指定移动的位数  a >> 2 输出结果 15 ,二进制解释: 0000 1111

 

实例练习:

#!/usr/bin/env python3

a = 10
b = 60
c = 0

#一下是数字转成二进制的方法
#例如取10,60数字的二进制
#128    64    32    16    8    4    2    1
#0      0     0     0     1    0    1    0      =   10
#0      0     1     1     1    1    0    0      =   60
#0      0     0     0     1    0    0    0      =   8
#
# 所以数字10,60,的二进制分别为
#     10 = 1010
#     60 = 111100

c = a & b   #按位与运算符:二进制位置中相对应的为1的则为1,否则为0
print(c)
#128    64    32    16    8    4    2    1
#0      0     0     0     1    0    1    0      =   a = 10
#0      0     1     1     1    1    0    0      =   b = 60
#0      0     0     0     1    0    0    0      =   c = a & b = 8

c = a | b   #按位或运算符:只要对应的位置是1的时候就是1
print(c)
#128    64    32    16    8    4    2    1
#0      0     0     0     1    0    1    0      =   a = 10
#0      0     1     1     1    1    0    0      =   b = 60
#0      0     1     1     1    1    1    0      =   c = a | b = 62

c = a ^ b   #按位异或运算符:就是相对应的位置不一样的时候等于1
print(c)
#128    64    32    16    8    4    2    1
#0      0     0     0     1    0    1    0      =   a = 10
#0      0     1     1     1    1    0    0      =   b = 60
#0      0     1     1     0    1    1    0      =   c = a ^ b = 54



c = a << 2  #做移动运算符:往左边移动两位相当于 10*(2**2)左移n位就是乘以2的n次方
print(c)
#128    64    32    16    8    4    2    1
#0      0     0     0     1    0    1    0      =   a = 10
#0      0     1     0     1    0    0    0      =   c = a << 2 = 40

c = a >> 2  #右移动运算符:往右边移动两位 
print(c)
#128    64    32    16    8    4    2    1
#0      0     0     0     1    0    1    0      =   a = 10
#0      0     0     0     0    0    1    0      =   c = a >>2 = 2

以上事例执行结果:

C:\\Python\\Python35\\python.exe E:/Python课程/s13/day2/运算符.py
8
62
54
40
2

Process finished with exit code 0

 

5、逻辑运算符:

 假设变量 a 为 10, b为 20:

运算符逻辑表达式描述实例
and x and y 布尔"与" - 如果 x 为 False,x and y 返回 False,否则它返回 y 的计算值。 (a and b) 返回 20
or x or y 布尔"或" - 如果 x 是 True,它返回 True,否则它返回 y 的计算值。 (a or b) 返回 10
not not x 布尔"非" - 如果 x 为 True,返回 False 。如果 x 为 False,它返回 True。 not(a and b) 返回 False

 

 

 

 

 

6、成员运算符:

运算符描述实例
in 如果在指定的序列中找到值返回 True,否则返回 False。 x 在 y 序列中 , 如果 x 在 y 序列中返回 True。
not in 如果在指定的序列中没有找到值返回 True,否则返回 False。 x 不在 y 序列中 , 如果 x 不在 y 序列中返回 True。

 

 

 

 

二、数据类型:

 

1、数字数据类型

 包含四种:

int整型 如:23、333

long长整型:就是比较大比较长的数字

     在32位机器上,整数的位数为32位,取值范围为-2**31~2**31-1,即-2147483648~2147483647
     在64位系统上,整数的位数为64位,取值范围为-2**63~2**63-1,即-9223372036854775808~9223372036854775807

     大于以上范围着都属于长整型,只不过局限于python2中,在python3中已经不存在了!

float(浮点型):顾名思义就是带有小数点的数字,占8个字节(64位),其中52位表示底,11位表示指数,剩下的一位表示符号。

complex(复数):复数由实数部分和虚数部分组成,一般形式为x+yj,其中的x是复数的实数部分,y是复数的虚数部分,这里的x和y都是实数。  

    注:Python中存在小数字池:-5 ~ 257
 
其中使用的函数:
abs(x) 返回数字的绝对值,如abs(-10) 返回 10

 

2、布尔值

  真或假(Ture、False)
  1 或 0
 
3、字符串(str)
例如:"hello world"  这就是字符串,其中字符串有很多种用法如下:
技术分享
  1 class str(basestring):
  2     """
  3     str(object=‘‘) -> string
  4     
  5     Return a nice string representation of the object.
  6     If the argument is a string, the return value is the same object.
  7     """
  8     def capitalize(self):  
  9         """ 首字母变大写 """
 10         """
 11         S.capitalize() -> string
 12         
 13         Return a copy of the string S with only its first character
 14         capitalized.
 15         """
 16         return ""
 17 
 18     def center(self, width, fillchar=None):  
 19         """ 内容居中,width:总长度;fillchar:空白处填充内容,默认无 """
 20         """
 21         S.center(width[, fillchar]) -> string
 22         
 23         Return S centered in a string of length width. Padding is
 24         done using the specified fill character (default is a space)
 25         """
 26         return ""
 27 
 28     def count(self, sub, start=None, end=None):  
 29         """ 子序列个数 """
 30         """
 31         S.count(sub[, start[, end]]) -> int
 32         
 33         Return the number of non-overlapping occurrences of substring sub in
 34         string S[start:end].  Optional arguments start and end are interpreted
 35         as in slice notation.
 36         """
 37         return 0
 38 
 39     def decode(self, encoding=None, errors=None):  
 40         """ 解码 """
 41         """
 42         S.decode([encoding[,errors]]) -> object
 43         
 44         Decodes S using the codec registered for encoding. encoding defaults
 45         to the default encoding. errors may be given to set a different error
 46         handling scheme. Default is ‘strict‘ meaning that encoding errors raise
 47         a UnicodeDecodeError. Other possible values are ‘ignore‘ and ‘replace‘
 48         as well as any other name registered with codecs.register_error that is
 49         able to handle UnicodeDecodeErrors.
 50         """
 51         return object()
 52 
 53     def encode(self, encoding=None, errors=None):  
 54         """ 编码,针对unicode """
 55         """
 56         S.encode([encoding[,errors]]) -> object
 57         
 58         Encodes S using the codec registered for encoding. encoding defaults
 59         to the default encoding. errors may be given to set a different error
 60         handling scheme. Default is ‘strict‘ meaning that encoding errors raise
 61         a UnicodeEncodeError. Other possible values are ‘ignore‘, ‘replace‘ and
 62         ‘xmlcharrefreplace‘ as well as any other name registered with
 63         codecs.register_error that is able to handle UnicodeEncodeErrors.
 64         """
 65         return object()
 66 
 67     def endswith(self, suffix, start=None, end=None):  
 68         """ 是否以 xxx 结束 """
 69         """
 70         S.endswith(suffix[, start[, end]]) -> bool
 71         
 72         Return True if S ends with the specified suffix, False otherwise.
 73         With optional start, test S beginning at that position.
 74         With optional end, stop comparing S at that position.
 75         suffix can also be a tuple of strings to try.
 76         """
 77         return False
 78 
 79     def expandtabs(self, tabsize=None):  
 80         """ 将tab转换成空格,默认一个tab转换成8个空格 """
 81         """
 82         S.expandtabs([tabsize]) -> string
 83         
 84         Return a copy of S where all tab characters are expanded using spaces.
 85         If tabsize is not given, a tab size of 8 characters is assumed.
 86         """
 87         return ""
 88 
 89     def find(self, sub, start=None, end=None):  
 90         """ 寻找子序列位置,如果没找到,返回 -1 """
 91         """
 92         S.find(sub [,start [,end]]) -> int
 93         
 94         Return the lowest index in S where substring sub is found,
 95         such that sub is contained within S[start:end].  Optional
 96         arguments start and end are interpreted as in slice notation.
 97         
 98         Return -1 on failure.
 99         """
100         return 0
101 
102     def format(*args, **kwargs): # known special case of str.format
103         """ 字符串格式化,动态参数,将函数式编程时细说 """
104         """
105         S.format(*args, **kwargs) -> string
106         
107         Return a formatted version of S, using substitutions from args and kwargs.
108         The substitutions are identified by braces (‘{‘ and ‘}‘).
109         """
110         pass
111 
112     def index(self, sub, start=None, end=None):  
113         """ 子序列位置,如果没找到,报错 """
114         S.index(sub [,start [,end]]) -> int
115         
116         Like S.find() but raise ValueError when the substring is not found.
117         """
118         return 0
119 
120     def isalnum(self):  
121         """ 是否是字母和数字 """
122         """
123         S.isalnum() -> bool
124         
125         Return True if all characters in S are alphanumeric
126         and there is at least one character in S, False otherwise.
127         """
128         return False
129 
130     def isalpha(self):  
131         """ 是否是字母 """
132         """
133         S.isalpha() -> bool
134         
135         Return True if all characters in S are alphabetic
136         and there is at least one character in S, False otherwise.
137         """
138         return False
139 
140     def isdigit(self):  
141         """ 是否是数字 """
142         """
143         S.isdigit() -> bool
144         
145         Return True if all characters in S are digits
146         and there is at least one character in S, False otherwise.
147         """
148         return False
149 
150     def islower(self):  
151         """ 是否小写 """
152         """
153         S.islower() -> bool
154         
155         Return True if all cased characters in S are lowercase and there is
156         at least one cased character in S, False otherwise.
157         """
158         return False
159 
160     def isspace(self):  
161         """
162         S.isspace() -> bool
163         
164         Return True if all characters in S are whitespace
165         and there is at least one character in S, False otherwise.
166         """
167         return False
168 
169     def istitle(self):  
170         """
171         S.istitle() -> bool
172         
173         Return True if S is a titlecased string and there is at least one
174         character in S, i.e. uppercase characters may only follow uncased
175         characters and lowercase characters only cased ones. Return False
176         otherwise.
177         """
178         return False
179 
180     def isupper(self):  
181         """
182         S.isupper() -> bool
183         
184         Return True if all cased characters in S are uppercase and there is
185         at least one cased character in S, False otherwise.
186         """
187         return False
188 
189     def join(self, iterable):  
190         """ 连接 """
191         """
192         S.join(iterable) -> string
193         
194         Return a string which is the concatenation of the strings in the
195         iterable.  The separator between elements is S.
196         """
197         return ""
198 
199     def ljust(self, width, fillchar=None):  
200         """ 内容左对齐,右侧填充 """
201         """
202         S.ljust(width[, fillchar]) -> string
203         
204         Return S left-justified in a string of length width. Padding is
205         done using the specified fill character (default is a space).
206         """
207         return ""
208 
209     def lower(self):  
210         """ 变小写 """
211         """
212         S.lower() -> string
213         
214         Return a copy of the string S converted to lowercase.
215         """
216         return ""
217 
218     def lstrip(self, chars=None):  
219         """ 移除左侧空白 """
220         """
221         S.lstrip([chars]) -> string or unicode
222         
223         Return a copy of the string S with leading whitespace removed.
224         If chars is given and not None, remove characters in chars instead.
225         If chars is unicode, S will be converted to unicode before stripping
226         """
227         return ""
228 
229     def partition(self, sep):  
230         """ 分割,前,中,后三部分 """
231         """
232         S.partition(sep) -> (head, sep, tail)
233         
234         Search for the separator sep in S, and return the part before it,
235         the separator itself, and the part after it.  If the separator is not
236         found, return S and two empty strings.
237         """
238         pass
239 
240     def replace(self, old, new, count=None):  
241         """ 替换 """
242         """
243         S.replace(old, new[, count]) -> string
244         
245         Return a copy of string S with all occurrences of substring
246         old replaced by new.  If the optional argument count is
247         given, only the first count occurrences are replaced.
248         """
249         return ""
250 
251     def rfind(self, sub, start=None, end=None):  
252         """
253         S.rfind(sub [,start [,end]]) -> int
254         
255         Return the highest index in S where substring sub is found,
256         such that sub is contained within S[start:end].  Optional
257         arguments start and end are interpreted as in slice notation.
258         
259         Return -1 on failure.
260         """
261         return 0
262 
263     def rindex(self, sub, start=None, end=None):  
264         """
265         S.rindex(sub [,start [,end]]) -> int
266         
267         Like S.rfind() but raise ValueError when the substring is not found.
268         """
269         return 0
270 
271     def rjust(self, width, fillchar=None):  
272         """
273         S.rjust(width[, fillchar]) -> string
274         
275         Return S right-justified in a string of length width. Padding is
276         done using the specified fill character (default is a space)
277         """
278         return ""
279 
280     def rpartition(self, sep):  
281         """
282         S.rpartition(sep) -> (head, sep, tail)
283         
284         Search for the separator sep in S, starting at the end of S, and return
285         the part before it, the separator itself, and the part after it.  If the
286         separator is not found, return two empty strings and S.
287         """
288         pass
289 
290     def rsplit(self, sep=None, maxsplit=None):  
291         """
292         S.rsplit([sep [,maxsplit]]) -> list of strings
293         
294         Return a list of the words in the string S, using sep as the
295         delimiter string, starting at the end of the string and working
296         to the front.  If maxsplit is given, at most maxsplit splits are
297         done. If sep is not specified or is None, any whitespace string
298         is a separator.
299         """
300         return []
301 
302     def rstrip(self, chars=None):  
303         """
304         S.rstrip([chars]) -> string or unicode
305         
306         Return a copy of the string S with trailing whitespace removed.
307         If chars is given and not None, remove characters in chars instead.
308         If chars is unicode, S will be converted to unicode before stripping
309         """
310         return ""
311 
312     def split(sel

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