CODEWITHSUNDEEP
python
Vijay47
Vijay47

Reputation: 377

Multi-line function calls with strings in python

I have a function call in python 2.7:

execute_cmd('/sbin/ip addr flush dev '
             + args.interface
             + ' && '
             + '/sbin/ifdown '
             + args.interface
             + ' ; '
             + '/sbin/ifup '
             + args.interface
             + ' && '
             + '/sbin/ifconfig | grep '
             + args.interface)

This is running fine, but pylint is complaining with the following warning messages:

C:220, 0: Wrong continued indentation (remove 1 space).
                    + args.interface
                   |^ (bad-continuation)
C:221, 0: Wrong continued indentation (remove 1 space).
                    + ' && '
                   |^ (bad-continuation)
C:222, 0: Wrong continued indentation (remove 1 space).
                    + '/sbin/ifconfig | grep '
                   |^ (bad-continuation)
.
.
.

What is the correct way to call a function in python with string argument(s) which spans across multiple lines?.

Upvotes: 0

Views: 2499

Answers (3)

Ruotong Jia
Ruotong Jia

Reputation: 41

I'd like to highlight the position of +, as pointed out in this post

Best practice:

income = (gross_wages
          + taxable_interest)

Anti-pattern: (In PEP8, this is W504 line break after binary operator)

income = (gross_wages +
          taxable_interest)

Upvotes: 0

Arne
Arne

Reputation: 20237

PEP 8 states that you can also start a long argument list (or anything within brackets, really) at the next line with one extra indentation level:

execute_cmd(
    '/sbin/ip addr flush dev ' +
    args.interface +
    ' && ' +
    '/sbin/ifdown ' +
    args.interface +
    ' ; ' +
    '/sbin/ifup ' +
    args.interface +
    ' && ' + 
    '/sbin/ifconfig | grep ' +
    args.interface
)

As I said in my comment, binary operators should be put at the end of a line break, not at the start of a new one.

What you can also do is use an fstring (python >3.6) and just drop the +s:

execute_cmd(
    f'/sbin/ip addr flush dev {args.interface} && /sbin/ifdown'
    f' {args.interface} ; /sbin/ifup {args.interface} && '
    f'/sbin/ifconfig | grep {args.interface}'
)

The same with the .format function (from python .. 2.6 onwards I think?):

execute_cmd(
    '/sbin/ip addr flush dev {0} && /sbin/ifdown' +
    ' {0} ; /sbin/ifup {0} && ' +
    '/sbin/ifconfig | grep {0}'.format(args.interface)
)

Upvotes: 0

Mel
Mel

Reputation: 6075

Pylint tells you exactly what to do, remove one space:

execute_cmd('/sbin/ip addr flush dev '
            + args.interface
            + ' && '
            + '/sbin/ifdown '
            + args.interface
            + ' ; '
            + '/sbin/ifup '
            + args.interface
            + ' && '
            + '/sbin/ifconfig | grep '
            + args.interface)

Also, you could use string formatting, for example:

command_line = '/sbin/ip addr flush dev {0} && /sbin/ifdown {0} ; /sbin/ifup {0} && {0} /sbin/ifconfig | grep {0}'\
    .format(args.interface)

Upvotes: 1

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