how to modify strings in a list of strings

Question

I would like to take a list of strings which represent individual lines entered in a CLI and put '~$ ' at the beginning so when I display them it is more clear that they are command lines. I tried this

command = # a multiline block of command lines
lines = command.split('\n')
for l in lines:
    l = '~$ ' + l
for l in lines: print l

But this modifies the temporary variable l I think without going back and changing the actual value in the list. If I put the print inside of the first loop it prints with the correct values, but if I do it like shown the change isn't made. Thanks in advance for any help.

Did you make any attempt at all to solve this on your own?

RyPeck
– RyPeck

2013-06-19 21:04:09 +00:00
Commented Jun 19, 2013 at 21:04 — RyPeck
– RyPeck, Commented Jun 19, 2013 at 21:04

Martijn Pieters · Accepted Answer · 2013-06-19 21:00:09Z

9

Use a list comprehension:

lines = ['~$ ' + line for line in command.split('\n')]

If you have to use a for loop, you'd use enumerate() to include an index so you can replace the individual items in the list:

for i, line in enumerate(lines):
    lines[i] = '~$ ' + line

edited Jun 19, 2013 at 21:00

answered Jun 19, 2013 at 20:59

Martijn Pieters

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7 Comments

Martijn Pieters Over a year ago

@mgilson: tsk, tsk, have you not yet learned that I keep on editing for a while? :-P

Elazar Over a year ago

note the new binding here, in case this is a global variable or something.

mgilson Over a year ago

I think I prefer slice-assignment here (over enumerate with the loop): lines[:] = ['~$ '+line for line in lines]

Martijn Pieters Over a year ago

@mgilson: if the list is references elsewhere, sure.

Elazar Over a year ago

the enumerate solution can be a bit misleading - it looks like independent values.

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michaelmeyer · Accepted Answer · 2013-06-19 21:09:02Z

1

The functional way:

list(map(lambda s: '~$ ' + s, command.splitlines()))

answered Jun 19, 2013 at 21:09

michaelmeyer

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