[ Python 常見問題 ] Restricting values of command line options

Source From Here 
Question 
How do I restrict the values of the argparse options? 

In the below code sau option should only accept a number of 0 or 1 and bg should only allow an integer. How can I implement this? 

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1. import os  
2. import sys, getopt  
3. import argparse  
4.   
5. def main ():  
6.     parser = argparse.ArgumentParser(description='Test script')  
7.     parser.add_argument('-sau','--set',action='store',dest='set',help=' Set flag',required=True)  
8.     parser.add_argument('-bg','--base_g',action='store',dest='base_g',help=' Base g',required=True)  
9.     results = parser.parse_args() # collect cmd line args  
10.     set = results.set  
11.     base_g = results.base_g  
12.   
13. if __name__ == '__main__':  
14.     main()  

How-To 
You can use the type and choices arguments of add_argument. To accept only '0' and '1', you'd do: 

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1. parser.add_argument(…, choices={"0", "1"})  

And to accept only integer numbers, you'd do: 

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1. parser.add_argument(…, type=int)  

Note that in choices, you’ll have to give the options in the type you specified as the type-argument. So to check for integers and allow only 0 and 1, you'd do: 

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1. parser.add_argument(…, type=int, choices={0, 1})  

Example: 

>>> import argparse 
>>> parser = argparse.ArgumentParser() 
>>> _ = parser.add_argument("-p", type=int, choices={0, 1}) 
>>> parser.parse_args(["-p", "0"]) 
Namespace(p=0)