python開發_python中的Boolean運算和真假值

python中的真假值：

Truth Value Testing

Any object can be tested for truth value, for use in an if or while condition or as operand of the Boolean operations below. The following values are considered false:

1.None

2.False

3.zero of any numeric type, for example, 0, 0.0, 0j.

4.any empty sequence, for example, '', (), [].

5.any empty mapping, for example, {}.

6.instances of user-defined classes, if the class defines a __bool__() or __len__() method, when that method returns the integer zero or bool value False. [1]

All other values are considered true — so objects of many types are always true.

Operations and built-in functions that have a Boolean result always return 0 or False for false and 1 or True for true, unless otherwise stated. (Important exception: the Boolean operations or and and always return one of their operands.)

總結：

#在python中，任何對象都可以判斷其真假值：True，False
#在if或while條件判斷中，下面的情況值為False：
#
# 1.None
# 2.Flase
# 3.數值為0的情況，如：0,0.0,0j
# 4.所有空序列，如：'',(),[]
# 5.所有空mapping，如：{}
# 6.instances of user-defined classes, if the class defines a __bool__() or __len__() method,
#    when that method returns the integer zero or bool value False.
#
# All other values are considered true — so objects of many types are always true.
#
#
# 在運算操作和內建函數返回Boolean結果0或者Flase表示false
#1或True表示true
#

python中的Boolean運算如下：

Boolean Operations

print('x or y -> if x is false,then y, else x ')
x, y = 2, 0
print('{} or {} = {}'.format(x, y, x or y))
x1, y1 = 0, 10
print('{} or {} = {}'.format(x1, y1, x1 or y1))
x2, y2 = 0, 0
print('{} or {} = {}'.format(x2, y2, x2 or y2))

print('#' * 50)
print('x and y -> if x is false,then x, else y ')
print('{} and {} = {}'.format(x, y, x and y))
x1, y1 = 0, 10
print('{} and {} = {}'.format(x1, y1, x1 and y1))
x2, y2 = 0, 0
print('{} and {} = {}'.format(x2, y2, x2 and y2))

print('#' * 50)
print('not x -> if x is false,then True,else False ')
x = 2
print('not {} = {}'.format(x, not x))
x = 0
print('not {} = {}'.format(x, not x))

 

運行效果：

Python 3.3.2 (v3.3.2:d047928ae3f6, May 16 2013, 00:03:43) [MSC v.1600 32 bit (Intel)] on win32
Type "copyright", "credits" or "license()" for more information.
>>> ================================ RESTART ================================
>>> 
x or y -> if x is false,then y, else x 
2 or 0 = 2
0 or 10 = 10
0 or 0 = 0
##################################################
x and y -> if x is false,then x, else y 
2 and 0 = 0
0 and 10 = 0
0 and 0 = 0
##################################################
not x -> if x is false,then True,else False 
not 2 = False
not 0 = True
>>>