python_day2学习笔记

基本数据类型

1、数字

int（整型）

　　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

  1 1）int --> string
  2 str是保留关键字，
  3 >>>a = 10
  4 >>>str1 = str(a)
  5 
  6 2)string --> int
  7 >>>x = "10"
  8 >>>y = int(x)

 1 >>> lists = ['a', 'b', 'e', 'c', 'd', 'a']
 2 >>> print '列表list转换为str:', ''.join(lists)
 3 结果：
 4 列表list转换为str: abecda
 5 
 6 >>>strs = 'hongten'
 7 >>>print '序列strs转换为list:', list(strs)
 8 结果：
 9 序列strs转换为list：['h', 'o', 'n', 'g', 't', 'e', 'n']
10 
11 >>>print '列表list转换为tuple:', tuple(lists)
12 结果：
13 列表list转换为tuple:（'h', 'o', 'n', 'g', 't', 'e', 'n'）
14 
15 >>>print '整数转换为字符chr:', chr(67)
16 结果：
17 整数转换为字符chr:'C'
18 
19 >>>print('字符chr转换为整数:', ord('C'))
20 结果：
21 字符chr转换为整数:67
22 
23 >>>print('整数转16进制数:', hex(12))
24 结果：：
25 整数转16进制数:'0xc'
26 
27 >>>print('整数转8进制数:', oct(12))
28 结果：
29 整数转8进制数:'014'

2、布尔值

在计算机内部，python使用1来表示True，而使用0来表示False。可以使用int数将布尔值转换为一个整数。

1 实例：
2 >>>print(int(True))
3 >>>1
4 
5 >>>print(int(False))
6 >>>0

也可以用bool函数将一个数字值转换成一个布尔值。如果值为0，这个函数返回False; 否则，这个函数总是返回True。

1 实例：
2 >>>print(bool(0))
3 >>>False
4 
5 >>>print(bool(1))
6 >>>True

3、字符串

a、处理字符串的函数

1 >>> s = "Welcome"
2 >>> len(s)
3 7
4 >>> max(s)
5 'o'
6 >>> min(s)
7 'W'

b、下标运算符

 1 >>> s = "Welcome"
 2 >>>for i in range(0, len(s), 2):
 3            print(s[i], end = '')
 4 >>>Wloe
 5 
 6 >>>s = "Welcome"
 7 >>>s[-1]
 8 'e'
 9 >>>s[-2]
10 'm'

c、截取运算符

1 >>> s = "Welcome"
2 >>> s[1:4]
3 'elc'
4 >>> s[ :6]
5 'Welcom'
6 >>> s[4: ]
7 'ome'
8 >>> s[1:-1]
9 'elcom'

d、in和not in 运算符

1 >>> s = "Welcome"
2 >>> 'come' in s
3 True
4 >>> 'come' not in s
5 False

e、比较字符串

 1 >>> "green" == "glow"
 2 False
 3 >>> "green" != "glow"
 4 True
 5 >>> "green" > "glow"
 6 True
 7 >>> "green" < "glow"
 8 False
 9 >>> "green" <= "glow"
10 False

f、搜索字串

 1 >>> s = "welcome to python"
 2 >>> s.endswith('thon')
 3 True
 4 >>> s.startswith("good")
 5 False
 6 >>> s.find("come")
 7 3
 8 >>> s.find("become")
 9 -1
10 >>> s.find("o")
11 4
12 >>> s.rfind("o")
13 15
14 >>> s.count("o")
15 3

g、转换字符串

 1 >>> s = "welcome to python"
 2 >>> s1 = s.capitalize()
 3 >>> s1
 4 'Welcome to python'
 5 >>> s2 = s.title()
 6 >>> s2
 7 'Welcome To Python'
 8 >>> s = "New England"
 9 >>> s3 = s.lower()
10 >>> s3
11 'new england'
12 >>> s4 = s.upper()
13 >>> s4
14 'NEW ENGLAND'
15 >>> s5 = s.swapcase()
16 >>> s5
17 'nEW eNGLAND'
18 >>> s6 = s.replace("England", "Haven")
19 >>> s6
20 'New Haven'
21 >>> s
22 'New England'

H、删除字符串的空格

 1 >>> s = "   Welcome to Python	"
 2 >>> s1 = s.lstrip()
 3 >>> s1
 4 'Welcome to Python	'
 5 >>> s2 = s.rstrip()
 6 >>> s2
 7 '   Welcome to Python'
 8 >>> s3 = s.strip()
 9 >>> s3
10 'Welcome to Python'

I、格式化字符串

 1 >>> s = "Welcome"
 2 >>> s1 = s.center(11)
 3 >>> s1
 4 '  Welcome  '
 5 >>> s2 = s.ljust(11)
 6 >>> s2
 7 'Welcome    '
 8 >>> s3 = s.rjust(11)
 9 >>> s3
10 '    Welcome'

4、列表

a、列表使用的函数

1 >>> list = [2,3,4,1,32]
2 >>> len(list)
3 5
4 >>> max(list)
5 32
6 >>> min(list)
7 1
8 >>> sum(list)
9 42

b、下标运算符

1 >>> list = [2,3,5,2,33,21]
2 >>> list[-1]
3 21
4 >>> list[-3]
5 2

c、列表截取

 1 >>> list = [2,3,5,2,33,21]
 2 >>> list[2:4]
 3 [5, 2]
 4 >>> list[:2]
 5 [2, 3]
 6 >>> list[3:]
 7 [2, 33, 21]
 8 >>> list[1:-3]
 9 [3, 5]
10 >>> list[-4:-2]
11 [5, 2]

d、列表方法

 1 >>> list = [2,3,4,1,32,4]
 2 >>> list.append(19)
 3 >>> list
 4 [2, 3, 4, 1, 32, 4, 19]
 5 >>> list.count(4)
 6 2
 7 >>> list2 = [99,54]
 8 >>> list.extend(list2)
 9 >>> list
10 [99, 25, 54, 99, 54, 99, 54]
11 >>> list.insert(1,25)
12 >>> list
13 [99, 25, 25, 54, 99, 54, 99, 54]

 1 >>> list1 = [2,25,3,4,1,32,4,1,32,4,19,99,54]
 2 >>> list.pop(2)
 3 25
 4 >>> list1
 5 [2, 25, 4, 1, 32, 4, 1, 32, 4, 19, 99, 54]
 6 >>> list1 = [2,25,3,4,1,32,4,1,32,4,19,99,54]
 7 >>> list.pop(2)
 8 25
 9 >>> list
10 [99, 25, 54, 99, 54, 99, 54]
11 >>> list1
12 [2, 25, 3, 4, 1, 32, 4, 1, 32, 4, 19, 99, 54]
13 >>>
14 >>>
15 >>> list1.pop(2)
16 3
17 >>> list1
18 [2, 25, 4, 1, 32, 4, 1, 32, 4, 19, 99, 54]
19 >>> list1.pop()
20 54
21 >>> list1
22 [2, 25, 4, 1, 32, 4, 1, 32, 4, 19, 99]
23 >>> list1.remove(32)
24 >>> list1
25 [2, 25, 4, 1, 4, 1, 32, 4, 19, 99]
26 >>> list1.reverse()
27 >>> list1
28 [99, 19, 4, 32, 1, 4, 1, 4, 25, 2]29 >>> list1.sort()
30 >>> list1
31 [1, 1, 2, 4, 4, 4, 19, 25, 32, 99]

e、enumerate遍历列表

 1 使用如下的方式遍历一个列表，但是缺点是无法读取索引index。
 2 >>> a = [3,4,5,2,3,7,8,9]
 3 >>> for i in a:
 4 ...    print i
 5 ...
 6 3
 7 4
 8 5
 9 2
10 3
11 7
12 8
13 9
14 

下面两种方法改进，如下举例：
17 >>> for index,item in enumerate(a):
18 ...     print index,item
19 ...
20 0 3
21 1 4
22 2 5
23 3 2
24 4 3
25 5 7
26 6 8
27 7 9
28 >>>
29 >>>
30 >>> for i in range(len(a)):
31 ...    print i,a[i]
32 ...
33 0 3
34 1 4
35 2 5
36 3 2
37 4 3
38 5 7
39 6 8
40 7 9
41 >>>

5、元组

元组跟列表类似，但是元组中的元素是固定的，也就是说，一旦一个元组被创建，就无法对元组中的元素进行添加、删除、替代或重新排序。

1 >>> tuple1 = ("green", "red", "blue")
2 >>> print tuple1
3 ('green', 'red', 'blue')
4 >>> tuple2 = tuple([7,1,2,23,4,5])
5 >>> print tuple2
6 (7, 1, 2, 23, 4, 5)

6、字典

字典是一个存储键值对集合的容器对象。它通过使用关键字实现快速、删除和更新值。

如创建字典语句：

students =  {”111-34-3434“:"John", "132-56-6290":"Peter"}

a、添加、删除举例：

1 >>> students = {"111-34-3434" : "John", "132-56-6290" : "Peter"}
2 >>> students["234-56-9010"] = "Susan"  #从字典添加条目
3 >>> students["234-56-9010"]
4 'Susan'
5 >>> del students["234-56-9010"]  #从字典删除一个条目

b、循环条目：

1 >>>students = {'111-34-3434': 'John Smith', '132-56-6290': 'Peter'}
2 >>> for key in students:
3 ...     print(key + ":" + str(students[key]))
4 ...
5 111-34-3434:John Smith
6 132-56-6290:Peter

c、len函数：

1 >>>students = {'111-34-3434': 'John Smith', '132-56-6290': 'Peter'}
2 >>>len(students)
3 2

d、检测一个关键字是否在字典中：

1 >>>students = {'111-34-3434': 'John Smith', '132-56-6290': 'Peter'}
2 >>> "111-34-3434" in students
3 True
4 >>> "998-34-3434" in students
5 False
6 >>>

e、相等性检测：

1 >>> d1 = {"red":41, "blue":3}
2 >>> d2 = {"blue":3, "red":41}
3 >>> d1 == d2
4 True
5 >>> d1 != d2
6 False
7 >>>

f、字典方法：

 1 >>> students = {"111-34-3434":"John", "132-56-6290":"Peter"}
 2 >>> tuple(students.keys())
 3 ('111-34-3434', '132-56-6290')
 4 >>> tuple(students.values())
 5 ('John', 'Peter')
 6 >>> tuple(students.items())
 7 (('111-34-3434', 'John'), ('132-56-6290', 'Peter'))
 8 >>> students.get("111-34-3434")
 9 'John'
10 >>> print(students.get("999-334-3434"))
11 None
12 >>> students.pop("111-34-3434")
13 'John'
14 >>> students
15 {'132-56-6290': 'Peter'}
16 >>> students.clear()
17 >>> students
18 {}
19 >>>

 1 dic = {'k1' : 123,'k2' : 456,'k4' : 111}
 2 n = dic.fromkeys(['k1','k2','k3'],[])
 3 print(n)
 4 n['k1'].append('x')
 5 print(n)
 6 
 7 运行结果如下：
 8 {'k2': [], 'k1': [], 'k3': []}
 9 {'k2': ['x'], 'k1': ['x'], 'k3': ['x']}
10 
11 dic = {'k1' : 123,'k2' : 456,'k4' : 111}
12 n = dic.fromkeys(['k1','k2','k3'],'alex')
13 print(n)
14 
15 运行结果如下：
16 {'k3': 'alex', 'k1': 'alex', 'k2': 'alex'}
17 
18 li = [11,22,44]
19 new_dict = dict(enumerate(li))
20 print(new_dict)
21 
22 运行结果如下：
23 {0: 11, 1: 22, 2: 44}
24 
25 
26 li = [11,22,44]
27 new_dict = dict(enumerate(li,10))
28 print(new_dict)
29 
30 运行结果如下：
31 {10: 11, 11: 22, 12: 44}
32 
33 t = (11,22,['alex',{'k1':"v1"}])
34 t[2][1]['k2'] = 123
35 print(t)
36 
37 运行结果如下：
38 (11, 22, ['alex', {'k1': 'v1', 'k2': 123}])
39 
40 t = (11,22,['alex',{'k1':"v1"}])
41 t[2][1].update({'k2':123})
42 print(t)
43 
44 运行结果如下：
45 (11, 22, ['alex', {'k1': 'v1', 'k2': 123}])