在python中打印一個變量

Question

我有這個在一個類中設置A或B的python代碼。我想打印什麼這個類接收：

if options.A: 
    print "setting A" 
    class TmpClass(A): pass 
else: 
    print "nothing set in the command line => setting to B" 
    class TmpClass(B): pass 

print "selected=",TmpClass 

我想看看A或B的輸出，但我看到：

selected= TmpClass 

Answer 1

你的代碼是幹什麼的，翻譯成英文是：

if option.A has a value that evaluates to True: 
    define an empty class called "TmpClass" that inherits from the object called "A" 
otherwise: 
    define an empty class called "TmpClass" that inherits from the object called "B" 

現在，如果什麼代碼實際上做的確實是您的本意，我猜測是，你想要什麼可以知道是否你的班級是以A或B爲基礎的......如果我是對的，那麼你想要在最後有一行：

print('TmpClass inherits from : %s' % TmpClass.__bases__) 

HTH！

Answer 2

A和B是傳遞給類在這裏正式參數， A和B

的不是實際值

Answer 3

您可以分配類變量，而無需創建它們的實例：

if options.A: 
    print "setting A" 
    TmpClass = A 
else: 
    print "nothing set in the command line => setting to B" 
    TmpClass = B 

print "selected=",TmpClass 

Answer 4

你可以看看使用isinstance（）。例如：

class MyBaseClass(): 
    def __init__(self): 
     self.cType = 'Base' 

    def whichClass(self): 
     print 'Class type = {0}'.format(self.cType) 

     if isinstance(self,DerivedClassA): 
      print 'Derived Class A' 
     elif isinstance(self,DerivedClassB): 
      print 'Derived Class B' 
     elif isinstance(self,MyBaseClass): 
      print 'Not A or B' 
     else: 
      print 'Unknown Class' 

class DerivedClassA(MyBaseClass): 
    def __init__(self): 
     self.cType = 'Class A' 

class DerivedClassB(MyBaseClass): 
    def __init__(self): 
     self.cType = 'Class B' 


Then Run: 

base = MyBaseClass() 
a = DerivedClassA() 
b = DerivedClassB() 
a.whichClass() 
>> Class type = Class A 
>> Derived Class A 
b.whichClass() 
>> Class type = Class B 
>> Derived Class B 
base.whichClass() 
>> Class type = Base 
>> Not A or B