Python argparse command line flags without arguments

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   I tried   parser add argument  -w     But I just get an error message saying   Usage  -w W  error  argument -w  expected one argument   which I take it means that it wants an argument value for the -w option  What s the way of just accepting a flag    I m finding http   docs python org library argparse html rather opaque on this question

User · Answer

Adding a quick snippet to have it ready to execute:

Source: myparser.py

import argparse
parser = argparse.ArgumentParser(description="Flip a switch by setting a flag")
parser.add_argument('-w', action='store_true')

args = parser.parse_args()
print args.w

Usage:

python myparser.py -w
>> True

User · Answer

Your script is right  But by default is of None type  So it considers true of any other value other than None is assigned to args argument name variable  I would suggest you to add a action  quot store true quot   This would make the True False type of flag  If used its True else False  import argparse parser   argparse ArgumentParser  parser-name   parser add argument  quot -f quot   quot --flag quot  action  quot store true quot  help  quot just a flag argument quot    usage   python3 script py -f  After parsing when checked with args f it returns true  args   parser parse args   print args f    gt  gt  gt true

User · Answer

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 here  specifically store true and store false  import argparse  parser   argparse ArgumentParser   parser add argument  -w   action  store true    where action  store true  implies default False  Conversely  you could haveaction  store false   which implies default True

User · Answer

Here s a quick way to do it  won t require anything besides sys   though functionality is limited    flag    --flag  in sys argv 1     1   is in case if the full file name is --flag

[python] Python argparse command line flags without arguments

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