变量、数据类型和运算符

本节目录

1、什么是变量?

2、常量

3、数字类型

4、布尔值

5、空值

6、运算符

什么是变量?

  变量是一种使用方便的占位符,用于引用计算机内存地址,使用变量并不需要了解变量在计算机内存中的地址,只要通过变量名引用变量就可以查看或更改变量的值(简单的说,变量就是一个用来存储数据的容器,方便后面的调用)

#声明变量

name=“Li”

  上述代码声明了一个变量,变量名为: name,变量name的值为:"Li"

  在Python中,等号=是赋值语句,可以把任意数据类型赋值给变量,同一个变量可以反复赋值,而且可以是不同类型的变量。这种变量本身类型不固定的语言称之为动态语言,与之对应的是静态语言。静态语言在定义变量时必须指定变量类型,如果赋值的时候类型不匹配,就会报错。例如Java是静态语言,和静态语言相比,动态语言更灵活,就是这个原因。

 

常量

  所谓常量就是不能变的变量,比如常用的数学常数π就是一个常量。在Python中,通常用全部大写的变量名表示常量:

PI=3.1415926

  但事实上PI仍然是一个变量,Python根本没有任何机制保证PI不会被改变,所以,用全部大写的变量名表示常量只是一个习惯上的用法,如果你一定要改变变量PI的值,也没人能拦住你。

 

数字类型

1、整数(int)

  Python可以处理任意大小的整数,当然包括负整数,在程序中的表示方法和数学上的写法一模一样,例如:1100-80800,等等。

计算机由于使用二进制,所以,有时候用十六进制表示整数比较方便,十六进制用0x前缀和0-9,a-f表示,例如:0xff000xa5b4c3d2,等等

class int(object):
    """
    int(x=0) -> int or long
    int(x, base=10) -> int or long
    
    Convert a number or string to an integer, or return 0 if no arguments
    are given.  If x is floating point, the conversion truncates towards zero.
    If x is outside the integer range, the function returns a long instead.
    
    If x is not a number or if base is given, then x must be a string or
    Unicode object representing an integer literal in the given base.  The
    literal can be preceded by '+' or '-' and be surrounded by whitespace.
    The base defaults to 10.  Valid bases are 0 and 2-36.  Base 0 means to
    interpret the base from the string as an integer literal.
    >>> int('0b100', base=0)
    4
    """
    def bit_length(self): 
        """ 返回表示该数字的时占用的最少位数 """
        """
        int.bit_length() -> int
        
        Number of bits necessary to represent self in binary.
        >>> bin(37)
        '0b100101'
        >>> (37).bit_length()
        6
        """
        return 0

    def conjugate(self, *args, **kwargs): # real signature unknown
        """ 返回该复数的共轭复数 """
        """ Returns self, the complex conjugate of any int. """
        pass

    def __abs__(self):
        """ 返回绝对值 """
        """ x.__abs__() <==> abs(x) """
        pass

    def __add__(self, y):
        """ x.__add__(y) <==> x+y """
        pass

    def __and__(self, y):
        """ x.__and__(y) <==> x&y """
        pass

    def __cmp__(self, y): 
        """ 比较两个数大小 """
        """ x.__cmp__(y) <==> cmp(x,y) """
        pass

    def __coerce__(self, y):
        """ 强制生成一个元组 """ 
        """ x.__coerce__(y) <==> coerce(x, y) """
        pass

    def __divmod__(self, y): 
        """ 相除,得到商和余数组成的元组 """ 
        """ x.__divmod__(y) <==> divmod(x, y) """
        pass

    def __div__(self, y): 
        """ x.__div__(y) <==> x/y """
        pass

    def __float__(self): 
        """ 转换为浮点类型 """ 
        """ x.__float__() <==> float(x) """
        pass

    def __floordiv__(self, y): 
        """ x.__floordiv__(y) <==> x//y """
        pass

    def __format__(self, *args, **kwargs): # real signature unknown
        pass

    def __getattribute__(self, name): 
        """ x.__getattribute__('name') <==> x.name """
        pass

    def __getnewargs__(self, *args, **kwargs): # real signature unknown
        """ 内部调用 __new__方法或创建对象时传入参数使用 """ 
        pass

    def __hash__(self): 
        """如果对象object为哈希表类型,返回对象object的哈希值。哈希值为整数。在字典查找中,哈希值用于快速比较字典的键。两个数值如果相等,则哈希值也相等。"""
        """ x.__hash__() <==> hash(x) """
        pass

    def __hex__(self): 
        """ 返回当前数的 十六进制 表示 """ 
        """ x.__hex__() <==> hex(x) """
        pass

    def __index__(self): 
        """ 用于切片,数字无意义 """
        """ x[y:z] <==> x[y.__index__():z.__index__()] """
        pass

    def __init__(self, x, base=10): # known special case of int.__init__
        """ 构造方法,执行 x = 123 或 x = int(10) 时,自动调用,暂时忽略 """ 
        """
        int(x=0) -> int or long
        int(x, base=10) -> int or long
        
        Convert a number or string to an integer, or return 0 if no arguments
        are given.  If x is floating point, the conversion truncates towards zero.
        If x is outside the integer range, the function returns a long instead.
        
        If x is not a number or if base is given, then x must be a string or
        Unicode object representing an integer literal in the given base.  The
        literal can be preceded by '+' or '-' and be surrounded by whitespace.
        The base defaults to 10.  Valid bases are 0 and 2-36.  Base 0 means to
        interpret the base from the string as an integer literal.
        >>> int('0b100', base=0)
        4
        # (copied from class doc)
        """
        pass

    def __int__(self): 
        """ 转换为整数 """ 
        """ x.__int__() <==> int(x) """
        pass

    def __invert__(self): 
        """ x.__invert__() <==> ~x """
        pass

    def __long__(self): 
        """ 转换为长整数 """ 
        """ x.__long__() <==> long(x) """
        pass

    def __lshift__(self, y): 
        """ x.__lshift__(y) <==> x<<y """
        pass

    def __mod__(self, y): 
        """ x.__mod__(y) <==> x%y """
        pass

    def __mul__(self, y): 
        """ x.__mul__(y) <==> x*y """
        pass

    def __neg__(self): 
        """ x.__neg__() <==> -x """
        pass

    @staticmethod # known case of __new__
    def __new__(S, *more): 
        """ T.__new__(S, ...) -> a new object with type S, a subtype of T """
        pass

    def __nonzero__(self): 
        """ x.__nonzero__() <==> x != 0 """
        pass

    def __oct__(self): 
        """ 返回改值的 八进制 表示 """ 
        """ x.__oct__() <==> oct(x) """
        pass

    def __or__(self, y): 
        """ x.__or__(y) <==> x|y """
        pass

    def __pos__(self): 
        """ x.__pos__() <==> +x """
        pass

    def __pow__(self, y, z=None): 
        """ 幂,次方 """ 
        """ x.__pow__(y[, z]) <==> pow(x, y[, z]) """
        pass

    def __radd__(self, y): 
        """ x.__radd__(y) <==> y+x """
        pass

    def __rand__(self, y): 
        """ x.__rand__(y) <==> y&x """
        pass

    def __rdivmod__(self, y): 
        """ x.__rdivmod__(y) <==> divmod(y, x) """
        pass

    def __rdiv__(self, y): 
        """ x.__rdiv__(y) <==> y/x """
        pass

    def __repr__(self): 
        """转化为解释器可读取的形式 """
        """ x.__repr__() <==> repr(x) """
        pass

    def __str__(self): 
        """转换为人阅读的形式,如果没有适于人阅读的解释形式的话,则返回解释器课阅读的形式"""
        """ x.__str__() <==> str(x) """
        pass

    def __rfloordiv__(self, y): 
        """ x.__rfloordiv__(y) <==> y//x """
        pass

    def __rlshift__(self, y): 
        """ x.__rlshift__(y) <==> y<<x """
        pass

    def __rmod__(self, y): 
        """ x.__rmod__(y) <==> y%x """
        pass

    def __rmul__(self, y): 
        """ x.__rmul__(y) <==> y*x """
        pass

    def __ror__(self, y): 
        """ x.__ror__(y) <==> y|x """
        pass

    def __rpow__(self, x, z=None): 
        """ y.__rpow__(x[, z]) <==> pow(x, y[, z]) """
        pass

    def __rrshift__(self, y): 
        """ x.__rrshift__(y) <==> y>>x """
        pass

    def __rshift__(self, y): 
        """ x.__rshift__(y) <==> x>>y """
        pass

    def __rsub__(self, y): 
        """ x.__rsub__(y) <==> y-x """
        pass

    def __rtruediv__(self, y): 
        """ x.__rtruediv__(y) <==> y/x """
        pass

    def __rxor__(self, y): 
        """ x.__rxor__(y) <==> y^x """
        pass

    def __sub__(self, y): 
        """ x.__sub__(y) <==> x-y """
        pass

    def __truediv__(self, y): 
        """ x.__truediv__(y) <==> x/y """
        pass

    def __trunc__(self, *args, **kwargs): 
        """ 返回数值被截取为整形的值,在整形中无意义 """
        pass

    def __xor__(self, y): 
        """ x.__xor__(y) <==> x^y """
        pass

    denominator = property(lambda self: object(), lambda self, v: None, lambda self: None)  # default
    """ 分母 = 1 """
    """the denominator of a rational number in lowest terms"""

    imag = property(lambda self: object(), lambda self, v: None, lambda self: None)  # default
    """ 虚数,无意义 """
    """the imaginary part of a complex number"""

    numerator = property(lambda self: object(), lambda self, v: None, lambda self: None)  # default
    """ 分子 = 数字大小 """
    """the numerator of a rational number in lowest terms"""

    real = property(lambda self: object(), lambda self, v: None, lambda self: None)  # default
    """ 实属,无意义 """
    """the real part of a complex number"""
复制代码
int

 

 

2、浮点数(float)

  浮点数也就是小数,之所以称为浮点数,是因为按照科学记数法表示时,一个浮点数的小数点位置是可变的,比如,1.23x109和12.3x108是完全相等的。浮点数可以用数学写法,如1.233.14-9.01,等等。但是对于很大或很小的浮点数,就必须用科学计数法表示,把10用e替代,1.23x109就是1.23e9,或者12.3e8,0.000012可以写成1.2e-5,等等。

  整数和浮点数在计算机内部存储的方式是不同的,整数运算永远是精确的(除法难道也是精确的?是的!),而浮点数运算则可能会有四舍五入的误差。

3、复数(complex)

  与数学中的复数概念一致,z=a+bj,a是实数部分,b是虚数部分,a和b都是浮点数类型,虚数部分用j或J标识

例:5.6+3j, -8.2+9j

  这三种类型存在一种逐渐“扩展”的关系:整数->浮点数->复数(整数是浮点数的特例,浮点数是复数的特例)

  不同的数字类型可以进行混合运算,运算后生成结果为最宽类型

 例:

#(整数+浮点数=浮点数)
>>> 125+2.0
127.0

布尔值

  布尔值和布尔代数的表示完全一致,一个布尔值只有TrueFalse两种值,要么是True,要么是False,在Python中,可以直接用TrueFalse表示布尔值(请注意大小写),也可以通过布尔运算计算出来:

>> True
True
>>> False
False
>>> 8> 9
False
>>> 6> 5
True

  布尔值可以用andornot运算。and运算是与运算,只有所有都为Trueand运算结果才是True

 空值

  空值是Python里一个特殊的值,用None表示。None不能理解为0,因为0是有意义的,而None是一个特殊的空值。

运算符

1、算数运算:

 

2、比较运算:

 

3、赋值运算:

 

4、逻辑运算:

 

5、成员运算:

posted @ 2017-01-12 13:27  似是故人来~  阅读(284)  评论(0编辑  收藏  举报