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 = ""
  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:''

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。

 实例：
 >>>print(int(True))
 >>>1

 >>>print(int(False))
 >>>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。

 实例：
 >>>print(bool(0))
 >>>False

 >>>print(bool(1))
 >>>True

3、字符串

a、处理字符串的函数

 >>> s = "Welcome"
 >>> len(s)
 7
 >>> max(s)
 'o'
 >>> min(s)
 'W'

b、下标运算符

 >>> s = "Welcome"
 >>>for i in range(0, len(s), 2):
            print(s[i], end = '')
 >>>Wloe

 >>>s = "Welcome"
 >>>s[-1]
 'e'
 >>>s[-2]
 'm'

c、截取运算符

 >>> s = "Welcome"
 >>> s[1:4]
 'elc'
 >>> s[ :6]
 'Welcom'
 >>> s[4: ]
 'ome'
 >>> s[1:-1]
 'elcom'

d、in和not in 运算符

 >>> s = "Welcome"
 >>> 'come' in s
 True
 >>> 'come' not in s
 False

e、比较字符串

 >>> "green" == "glow"
 False
 >>> "green" != "glow"
 True
 >>> "green" > "glow"
 True
 >>> "green" < "glow"
 False
 >>> "green" <= "glow"
 False

f、搜索字串

 >>> s = "welcome to python"
 >>> s.endswith('thon')
 True
 >>> s.startswith("good")
 False
 >>> s.find("come")
 3
 >>> s.find("become")
 -1
 >>> s.find("o")
 4
 >>> s.rfind("o")
 15
 >>> s.count("o")
 3

g、转换字符串

 >>> s = "welcome to python"
 >>> s1 = s.capitalize()
 >>> s1
 'Welcome to python'
 >>> s2 = s.title()
 >>> s2
 'Welcome To Python'
 >>> s = "New England"
 >>> s3 = s.lower()
 >>> s3
 'new england'
 >>> s4 = s.upper()
 >>> s4
 'NEW ENGLAND'
 >>> s5 = s.swapcase()
 >>> s5
 'nEW eNGLAND'
 >>> s6 = s.replace("England", "Haven")
 >>> s6
 'New Haven'
 >>> s
 'New England'

H、删除字符串的空格

 >>> s = "   Welcome to Python\t"
 >>> s1 = s.lstrip()
 >>> s1
 'Welcome to Python\t'
 >>> s2 = s.rstrip()
 >>> s2
 '   Welcome to Python'
 >>> s3 = s.strip()
 >>> s3
 'Welcome to Python'

I、格式化字符串

 >>> s = "Welcome"
 >>> s1 = s.center(11)
 >>> s1
 '  Welcome  '
 >>> s2 = s.ljust(11)
 >>> s2
 'Welcome    '
 >>> s3 = s.rjust(11)
 >>> s3
 '    Welcome'

4、列表

a、列表使用的函数

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

b、下标运算符

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

c、列表截取

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

d、列表方法

 >>> list = [2,3,4,1,32,4]
 >>> list.append(19)
 >>> list
 [2, 3, 4, 1, 32, 4, 19]
 >>> list.count(4)
 2
 >>> list2 = [99,54]
 >>> list.extend(list2)
 >>> list
 [99, 25, 54, 99, 54, 99, 54]
 >>> list.insert(1,25)
 >>> list
 [99, 25, 25, 54, 99, 54, 99, 54]

 >>> list1 = [2,25,3,4,1,32,4,1,32,4,19,99,54]
 >>> list.pop(2)
 25
 >>> list1
 [2, 25, 4, 1, 32, 4, 1, 32, 4, 19, 99, 54]
 >>> list1 = [2,25,3,4,1,32,4,1,32,4,19,99,54]
 >>> list.pop(2)
 25
 >>> list
 [99, 25, 54, 99, 54, 99, 54]
 >>> list1
 [2, 25, 3, 4, 1, 32, 4, 1, 32, 4, 19, 99, 54]
 >>>
 >>>
 >>> list1.pop(2)
 3
 >>> list1
 [2, 25, 4, 1, 32, 4, 1, 32, 4, 19, 99, 54]
 >>> list1.pop()
 54
 >>> list1
 [2, 25, 4, 1, 32, 4, 1, 32, 4, 19, 99]
 >>> list1.remove(32)
 >>> list1
 [2, 25, 4, 1, 4, 1, 32, 4, 19, 99]
 >>> list1.reverse()
 >>> list1
 [99, 19, 4, 32, 1, 4, 1, 4, 25, 2] >>> list1.sort()
 >>> list1
 [1, 1, 2, 4, 4, 4, 19, 25, 32, 99]

e、enumerate遍历列表

 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。
 >>> a = [3,4,5,2,3,7,8,9]
 >>> for i in a:
 ...    print i
 ...
 3
 4
 5
 2
 3
 7
 8
 9

下面两种方法改进，如下举例：
 >>> for index,item in enumerate(a):
 ...     print index,item
 ...
 0 3
 1 4
 2 5
 3 2
 4 3
 5 7
 6 8
 7 9
 >>>
 >>>
 >>> for i in range(len(a)):
 ...    print i,a[i]
 ...
 0 3
 1 4
 2 5
 3 2
 4 3
 5 7
 6 8
 7 9
 >>>

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。

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

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

b、循环条目：

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

c、len函数：

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

d、检测一个关键字是否在字典中：

 >>>students = {'111-34-3434': 'John Smith', '132-56-6290': 'Peter'}
 >>> "111-34-3434" in students
 True
 >>> "998-34-3434" in students
 False
 >>>

e、相等性检测：

 >>> d1 = {"red":41, "blue":3}
 >>> d2 = {"blue":3, "red":41}
 >>> d1 == d2
 True
 >>> d1 != d2
 False
 >>>

f、字典方法：

 >>> students = {"111-34-3434":"John", "132-56-6290":"Peter"}
 >>> tuple(students.keys())
 ('111-34-3434', '132-56-6290')
 >>> tuple(students.values())
 ('John', 'Peter')
 >>> tuple(students.items())
 (('111-34-3434', 'John'), ('132-56-6290', 'Peter'))
 >>> students.get("111-34-3434")
 'John'
 >>> print(students.get("999-334-3434"))
 None
 >>> students.pop("111-34-3434")
 'John'
 >>> students
 {'132-56-6290': 'Peter'}
 >>> students.clear()
 >>> students
 {}
 >>>

 dic = {'k1' : 123,'k2' : 456,'k4' : 111}
 n = dic.fromkeys(['k1','k2','k3'],[])
 print(n)
 n['k1'].append('x')
 print(n)

 运行结果如下：
 {'k2': [], 'k1': [], 'k3': []}
 {'k2': ['x'], 'k1': ['x'], 'k3': ['x']}

 dic = {'k1' : 123,'k2' : 456,'k4' : 111}
 n = dic.fromkeys(['k1','k2','k3'],'alex')
 print(n)

 运行结果如下：
 {'k3': 'alex', 'k1': 'alex', 'k2': 'alex'}

 li = [11,22,44]
 new_dict = dict(enumerate(li))
 print(new_dict)

 运行结果如下：
 {0: 11, 1: 22, 2: 44}

 li = [11,22,44]
 new_dict = dict(enumerate(li,10))
 print(new_dict)

 运行结果如下：
 {10: 11, 11: 22, 12: 44}

 t = (11,22,['alex',{'k1':"v1"}])
 t[2][1]['k2'] = 123
 print(t)

 运行结果如下：
 (11, 22, ['alex', {'k1': 'v1', 'k2': 123}])

 t = (11,22,['alex',{'k1':"v1"}])
 t[2][1].update({'k2':123})
 print(t)

 运行结果如下：
 (11, 22, ['alex', {'k1': 'v1', 'k2': 123}])