argparse store false if unspecified
PythonCommand Line-ArgumentsArgparsePython Problem Overview
parser.add_argument('-auto', action='store_true')
How can I store false if -auto
is unspecified? I can faintly remember that this way, it stores None if unspecified
Python Solutions
Solution 1 - Python
The store_true
option automatically creates a default value of False.
Likewise, store_false
will default to True when the command-line argument is not present.
The source for this behavior is succinct and clear: http://hg.python.org/cpython/file/2.7/Lib/argparse.py#l861
The argparse docs aren't clear on the subject, so I'll update them now: http://hg.python.org/cpython/rev/49677cc6d83a
Solution 2 - Python
With
import argparse
parser=argparse.ArgumentParser()
parser.add_argument('-auto', action='store_true', )
args=parser.parse_args()
print(args)
running
% test.py
yields
Namespace(auto=False)
So it appears to be storing False
by default.
Solution 3 - Python
Raymond Hettinger answers OP's question already.
However, my group has experienced readability issues using "store_false". Especially when new members join our group. This is because it is most intuitive way to think is that when a user specifies an argument, the value corresponding to that argument will be True or 1.
For example, if the code is -
parser.add_argument('--stop_logging', action='store_false')
The code reader may likely expect the logging statement to be off when the value in stop_logging is true. But code such as the following will lead to the opposite of the desired behavior -
if not stop_logging:
#log
On the other hand, if the interface is defined as the following, then the "if-statement" works and is more intuitive to read -
parser.add_argument('--stop_logging', action='store_true')
if not stop_logging:
#log
Solution 4 - Python
store_false will actually default to 0
by default (you can test to verify). To change what it defaults to, just add default=True
to your declaration.
So in this case:
parser.add_argument('-auto', action='store_true', default=True)