How to pass an entire list as command line argument in Python?
Question:
I was trying to pass two lists containing integers as arguments to a python code. But sys.argv[i] gets the parameters as a list of string.
Input would look like,
$ python filename.py [2,3,4,5] [1,2,3,4]
I found the following hack to convert the list.
strA = sys.argv[1].replace('[', ' ').replace(']', ' ').replace(',', ' ').split()
strB = sys.argv[2].replace('[', ' ').replace(']', ' ').replace(',', ' ').split()
A = [float(i) for i in strA]
B = [float (i) for i in strB]
Is there a better way to do this?
Answers:
No, there is no way pass a list in a command line argument. Command line arguments are always string. But there is a better way to convert it to list. You can do it like that:
import ast
A = ast.literal_eval(strA)
B = ast.literal_eval(strB)
I tested this on my end, and my input looks like this:
python foo.py "[1,2,3,4]" "[5,6,7,8,9]"
I’m doing the following to convert the two params of interest:
import ast
import sys
list1 = ast.literal_eval(sys.argv[1])
list2 = ast.literal_eval(sys.argv[2])
You have to escape:
python some.py [2,3,4,5] [1,2,3,4]
some.py
import sys
print sys.argv[1]
print sys.argv[2]
this gives me:
[2,3,4,5]
[1,2,3,4]
UPDATE:
import sys
import ast
d = ast.literal_eval(sys.argv[1])
b = ast.literal_eval(sys.argv[2])
for a in d:
print a
for e in b:
print e
first will give:
2
3
4
5
and second will give
1
2
3
4
Why not:
python foo.py 1,2,3,4 5,6,7,8
Much cleaner than trying to eval python and doesn’t require your user to know python format.
import sys
list1 = sys.argv[1].split(',')
list2 = [int(c) for c in sys.argv[2].split(',')] # if you want ints
Don’t reinvent the wheel. Use the argparse module, be explicit and pass in actual lists of parameters
import argparse
# defined command line options
# this also generates --help and error handling
CLI=argparse.ArgumentParser()
CLI.add_argument(
"--lista", # name on the CLI - drop the `--` for positional/required parameters
nargs="*", # 0 or more values expected => creates a list
type=int,
default=[1, 2, 3], # default if nothing is provided
)
CLI.add_argument(
"--listb",
nargs="*",
type=float, # any type/callable can be used here
default=[],
)
# parse the command line
args = CLI.parse_args()
# access CLI options
print("lista: %r" % args.lista)
print("listb: %r" % args.listb)
You can then call it using
$ python my_app.py --listb 5 6 7 8 --lista 1 2 3 4
lista: [1, 2, 3, 4]
listb: [5.0, 6.0, 7.0, 8.0]
Command line arguments are always passed as strings. You will need to parse them into your required data type yourself.
>>> input = "[2,3,4,5]"
>>> map(float, input.strip('[]').split(','))
[2.0, 3.0, 4.0, 5.0]
>>> A = map(float, input.strip('[]').split(','))
>>> print(A, type(A))
([2.0, 3.0, 4.0, 5.0], <type 'list'>)
There are libraries like argparse and click that let you define your own argument type conversion but argparse treats "[2,3,4]" the same as [ 2 , 3 , 4 ] so I doubt it will be useful.
edit Jan 2019 This answer seems to get a bit of action still so I’ll add another option taken directly from the argparse docs.
You can use action=append to allow repeated arguments to be collected into a single list.
>>> parser = argparse.ArgumentParser()
>>> parser.add_argument('--foo', action='append')
>>> parser.parse_args('--foo 1 --foo 2'.split())
Namespace(foo=['1', '2'])
In this case you would pass --foo ? once for each list item. Using OPs example: python filename.py --foo 2 --foo 3 --foo 4 --foo 5 would result in foo=[2,3,4,5]
You can also do the following:
say, you have foo.py :
import json
import sys
data = json.loads(sys.argv[1])
print data, type(data)
Then if you run the above as : python foo.py "[1,2,3]"
Output:
[1, 2, 3] <type 'list'>
You can simply use nargs='+' option of argparse
import argparse
parser = argparse.ArgumentParser()
parser.add_argument('--myarg', dest='myarg', required=False, help='--myarg 100 100 100 takes a list of 3 elements, each is of value 100 ', nargs='+', type=int, default=[100,100,100])
You can then pass arguments like this:
python your_file.py --myarg 1 2 3
This will be stored in your program in myarg as [1,2,3]
print(myarg)
Outputs:
[1,2,3]
I was trying to pass two lists containing integers as arguments to a python code. But sys.argv[i] gets the parameters as a list of string.
Input would look like,
$ python filename.py [2,3,4,5] [1,2,3,4]
I found the following hack to convert the list.
strA = sys.argv[1].replace('[', ' ').replace(']', ' ').replace(',', ' ').split()
strB = sys.argv[2].replace('[', ' ').replace(']', ' ').replace(',', ' ').split()
A = [float(i) for i in strA]
B = [float (i) for i in strB]
Is there a better way to do this?
No, there is no way pass a list in a command line argument. Command line arguments are always string. But there is a better way to convert it to list. You can do it like that:
import ast
A = ast.literal_eval(strA)
B = ast.literal_eval(strB)
I tested this on my end, and my input looks like this:
python foo.py "[1,2,3,4]" "[5,6,7,8,9]"
I’m doing the following to convert the two params of interest:
import ast
import sys
list1 = ast.literal_eval(sys.argv[1])
list2 = ast.literal_eval(sys.argv[2])
You have to escape:
python some.py [2,3,4,5] [1,2,3,4]
some.py
import sys
print sys.argv[1]
print sys.argv[2]
this gives me:
[2,3,4,5]
[1,2,3,4]
UPDATE:
import sys
import ast
d = ast.literal_eval(sys.argv[1])
b = ast.literal_eval(sys.argv[2])
for a in d:
print a
for e in b:
print e
first will give:
2
3
4
5
and second will give
1
2
3
4
Why not:
python foo.py 1,2,3,4 5,6,7,8
Much cleaner than trying to eval python and doesn’t require your user to know python format.
import sys
list1 = sys.argv[1].split(',')
list2 = [int(c) for c in sys.argv[2].split(',')] # if you want ints
Don’t reinvent the wheel. Use the argparse module, be explicit and pass in actual lists of parameters
import argparse
# defined command line options
# this also generates --help and error handling
CLI=argparse.ArgumentParser()
CLI.add_argument(
"--lista", # name on the CLI - drop the `--` for positional/required parameters
nargs="*", # 0 or more values expected => creates a list
type=int,
default=[1, 2, 3], # default if nothing is provided
)
CLI.add_argument(
"--listb",
nargs="*",
type=float, # any type/callable can be used here
default=[],
)
# parse the command line
args = CLI.parse_args()
# access CLI options
print("lista: %r" % args.lista)
print("listb: %r" % args.listb)
You can then call it using
$ python my_app.py --listb 5 6 7 8 --lista 1 2 3 4
lista: [1, 2, 3, 4]
listb: [5.0, 6.0, 7.0, 8.0]
Command line arguments are always passed as strings. You will need to parse them into your required data type yourself.
>>> input = "[2,3,4,5]"
>>> map(float, input.strip('[]').split(','))
[2.0, 3.0, 4.0, 5.0]
>>> A = map(float, input.strip('[]').split(','))
>>> print(A, type(A))
([2.0, 3.0, 4.0, 5.0], <type 'list'>)
There are libraries like argparse and click that let you define your own argument type conversion but argparse treats "[2,3,4]" the same as [ 2 , 3 , 4 ] so I doubt it will be useful.
edit Jan 2019 This answer seems to get a bit of action still so I’ll add another option taken directly from the argparse docs.
You can use action=append to allow repeated arguments to be collected into a single list.
>>> parser = argparse.ArgumentParser()
>>> parser.add_argument('--foo', action='append')
>>> parser.parse_args('--foo 1 --foo 2'.split())
Namespace(foo=['1', '2'])
In this case you would pass --foo ? once for each list item. Using OPs example: python filename.py --foo 2 --foo 3 --foo 4 --foo 5 would result in foo=[2,3,4,5]
You can also do the following:
say, you have foo.py :
import json
import sys
data = json.loads(sys.argv[1])
print data, type(data)
Then if you run the above as : python foo.py "[1,2,3]"
Output:
[1, 2, 3] <type 'list'>
You can simply use nargs='+' option of argparse
import argparse
parser = argparse.ArgumentParser()
parser.add_argument('--myarg', dest='myarg', required=False, help='--myarg 100 100 100 takes a list of 3 elements, each is of value 100 ', nargs='+', type=int, default=[100,100,100])
You can then pass arguments like this:
python your_file.py --myarg 1 2 3
This will be stored in your program in myarg as [1,2,3]
print(myarg)
Outputs:
[1,2,3]