2.变量类型-python笔记

变量赋值

  变量的本质是，开辟的一块内存，用来存放值。给变量赋值很容易：

#!/usr/local/bin/python2.7count1=100count2=1000.9count3="What the fuck."print count1,'\n',count2,'\n',count3

连续赋同一个值：a=b=c=1，那么a b c共享同一块存储区，存储的值为1.

连续分别赋值：a,b,c = 2, 4, "hey"那就是三个不同变量。

基本数据类型

数字Numbers

赋值：val=20   val2=3.242等。不管是什么数值类型，直接赋值即可。

删除赋值：del val,val2

python支持的四种数值类型：int long float complex。例子如下表

字符串String

引号之间的字符，构成字符串。

可以用+将两个字符串连起来，用*使得字符串重复自身，变长。

    

另外，字符串的子串，可以用[:]提取出来。比如：

#!/usr/bin/pythonstr = 'Hello World!'print str          # 打印全字符串print str[0]       # 打印第一个字符Hprint str[2:5]     # 打印第三到第五个字符print str[2:]      # 打印从第三个字符到末尾的所有字符print str * 2      # Prints string two timesprint str + "TEST" # Prints concatenated string

列表List

列表用[ ]标识。是python最通用的复合数据类型。看这段代码就明白。

#!/usr/bin/pythonlist = [ 'abcd', 786 , 2.23, 'john', 70.2 ]tinylist = [123, 'john']print list          # Prints complete listprint list[0]       # Prints first element of the listprint list[1:3]     # Prints elements starting from 2nd till 3rd print list[2:]      # Prints elements starting from 3rd elementprint tinylist * 2  # Prints list two timesprint list + tinylist # Prints concatenated lists

列表的元素用逗号隔开，是可以对某元素多次赋值的。

元组Tuple

元组用()标识。内部元素用逗号隔开。但是元素不能二次赋值，相当于只读列表。

#!/usr/bin/pythontuple = ( 'abcd', 786 , 2.23, 'john', 70.2  )tinytuple = (123, 'john')print tuple           # Prints complete listprint tuple[0]        # Prints first element of the listprint tuple[1:3]      # Prints elements starting from 2nd till 3rd print tuple[2:]       # Prints elements starting from 3rd elementprint tinytuple * 2   # Prints list two timesprint tuple + tinytuple # Prints concatenated lists

字典Dictionary

字典用{ }标识。字典由索引(key)和它对应的值value组成。

#!/usr/bin/pythondict = {}dict['one'] = "This is one"dict[2]     = "This is two"tinydict = {'name': 'john','code':6734, 'dept': 'sales'}print dict['one']       # Prints value for 'one' keyprint dict[2]           # Prints value for 2 keyprint tinydict          # Prints complete dictionaryprint tinydict.keys()   # Prints all the keysprint tinydict.values() # Prints all the values

对字典dict，one 、2就是索引。而"This is one"和"This is two"就是相对应的值。

字典的元素是没有排序的。

dict.keys()返回所有key，dict.values()返回所有value值。

变量类型转换

int(x [,base])
Converts x to an integer. base specifies the base if x is a string.

long(x [,base] )
Converts x to a long integer. base specifies the base if x is a string.

float(x)
Converts x to a floating-point number.

complex(real [,imag])
Creates a complex number.

str(x)
Converts object x to a string representation.

repr(x)
Converts object x to an expression string.

eval(str)
Evaluates a string and returns an object.

tuple(s)
Converts s to a tuple.

list(s)
Converts s to a list.

set(s)
Converts s to a set.

dict(d)
Creates a dictionary. d must be a sequence of (key,value) tuples.

frozenset(s)
Converts s to a frozen set.

chr(x)
Converts an integer to a character.

unichr(x)
Converts an integer to a Unicode character.

ord(x)
Converts a single character to its integer value.

hex(x)
Converts an integer to a hexadecimal string.

oct(x)
Converts an integer to an octal string.