True and True ==> True True or True ==> True
True and False ==> False True or False ==> True
False and True ==> False False or True ==> True
False and False ==> False False or False ==> False
a='b'
c='dd'
print(c or a)#是下面这个意思
if c:
print(c)
else:
print(a)
#结果：
dd
dd
print(c and a)
if c:
print(a)
else:
print(c)
#结果：
b
b
