Using python to change directory information with one-liner code

Question

I have this code to change directory information in python. I'd like to change '/a/b/c' into '/x/b/c'.

import os x = "/a/b/c" y = x.split(os.sep) y[1] = 'x' os.sep.join(y)

Now I just want to know if python can make it one-liner. I can't simply use os.sep.join(x.split(os.sep)[1] = 'x') as it causes an syntax error. What might be other options in python?

Why do you have to do it in one line?

Jakob Bowyer
– Jakob Bowyer

2012-12-28 15:00:00 +00:00
Commented Dec 28, 2012 at 15:00 — Jakob Bowyer
– Jakob Bowyer, Commented Dec 28, 2012 at 15:00

Mattie B · Accepted Answer · 2012-12-28 15:15:05Z

os.sep.join('x' if idx == 1 else element for idx, element in enumerate(x.split(os.sep)))

result:

'/x/b/c'

Explanation: enumerate pairs each element of x.split(os.sep) with its index. 'x' if idx == 1 else element replaces the element with 'x' if it is the 1th element, and leaves it intact otherwise.

Mattie B · Accepted Answer · 2012-12-28 15:03:01Z

2

This is likely rather inefficient:

y = os.sep.join([x.split(os.sep)[0]] + ['x'] + x.split(os.sep)[2:])

answered Dec 28, 2012 at 15:03

Mattie B

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3 Comments

Kevin Over a year ago

If you don't want to call split twice, you could use a lambda function, like this: (lambda elements: os.sep.join([elements[0]] + ['x'] + elements[2:]))(x.split(os.sep))

Mattie B Over a year ago

@Kevin That's pretty clever! I like it.

Kevin Over a year ago

Yes, it's very useful for one-liners, since assignment is impossible. Whenever you ask yourself, "how do I calculate a value once and use it multiple times later?", consider using lambda.

doru · Accepted Answer · 2012-12-28 15:20:40Z

0

This seems to work too:

y = os.sep + 'x'+ x[2:]

answered Dec 28, 2012 at 15:20

doru

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1 Comment

Mattie B Over a year ago

It does for the example case, but would fail in a number of situations, such as x not starting with os.sep, the top-level directory contained more than one character, if os.sep itself wasn't a single character... this is why using os.path functions is so important.

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