[ Python 常見問題 ] Python argparse command line flags without arguments

Source From Here 
Question 
How do I add an optional flag to my command line args? eg. so I can write 

# python myprog.py

or 

# python myprog.py -w // No value required for argument -w

How-To 
As you have it, the argument w is expecting a value after -w on the command line. If you are just looking to flip a switch by setting a variable True or False, have a look at http://docs.python.org/dev/library/argparse.html#action (specifically store_true and store_false). e.g.: 
- test.py 

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1. #!/usr/bin/env python  
2. import argparse  
3.   
4. import argparse  
5.   
6. parser = argparse.ArgumentParser(description='For testing')  
7. parser.add_argument('-w', action='store_true', default=False)  
8. args = parser.parse_args()  
9.   
10. if args.w:  
11.     print("Turn on switch")  
12. else:  
13.     print("Turn off switch")  

Test it this way: 

# ./test.py 
Turn off switch 
# ./test.py -w 
Turn on switch