if a != None:

>>> x = 1

>>> not x

False

>>> x = [1]

>>> not x

False

>>> x = 0

>>> not x

True

>>> x = [0] # You don't want to fall in this one.

>>> not x

False

在python中 None, False, 空字符串"", 0, 空列表[], 空字典{}, 空元组()都相当于False ，即：
not None == not False == not '' == not 0 == not [] == not {} == not ()

if a != None:

其意思是a!=none,则执行:后面的语句

转载于:https://www.cnblogs.com/fcfc940503/p/11095009.html

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