How do I insert a list at the front of another list?

Question

>>> a = ['foo.py']
>>> k = ['nice', '-n', '10'] 
>>> a.insert(0, k)
>>> a
[['nice', '-n', '10'], 'foo.py']

I want to list k to be on the same level as foo.py, rather than a sublist.

Asked By: canadadry

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Source

Answer 1

Apply slicing:

a[0:0] = k

Or do it manually:

a = k + a

The first approach remain the same for insertion at any place, i.e. a[n:n] = k
would insert k at position n, but the second approach would not be the same, that will be

a = a[:n] + k + a[n:]

Answered By: Sufian Latif

Answer 2

>>> k + a
['nice', '-n', '10', 'foo.py']

Answered By: dhg

Answer 3

Use list concatenation:

a = k + a

Answered By: David Robinson

Answer 4

instead of:

>>> a.insert(0, k)

use:

>>> k.extend(a)
>>> k
['nice', '-n', '10', 'foo.py']

this updates the “k” list “in place” instead of creating a copy.

the list concatenation (k + a) will create a copy.

the slicing option (a[0:0] = k) will also update “in place” but IMHO is harder to read.

Answered By: Paulo Scardine

Answer 5

>>> a = ['foo.py']
>>> k = ['nice', '-n', '10']
>>> k.extend(a)
>>> print k
['nice', '-n', '10', 'foo.py']

Answered By: thavan

Answer 6

    list1=list(xrange(1,11)) # numbers 1 to 10 in list
    list1[:0]=[0,0,0] # adds triple 0s to front of list
    list1+=[11,12,13] #adds [11,12,13] to the end of list
    print list1

Answered By: Stefan Gruenwald

How do I insert a list at the front of another list?

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