How to permute a list of elements in sage

[jianrong]

Dear All,

I am trying to write a function in sage to permute a list of elements.

def f(i, v1):
v=[]
for j in v1:
v.append(j)

print(v)
v[i+1]=v1[i]
v[i]=v1[i+1]
return v

But the above codes do not work. I couldn't figure out the mistake. Thank you very much.

[Justin C. Walker]

It would help to know what “codes do not work” means. Do you get an error message, or does the function f() not produce the result you want.

It may be that you do not have much experience with the Python programming language. There is extensive documentation available at <https://python.org>.

In case your copy of the code you are writing was exactly what you used, the problem may be that you are not following the indentation rules that Python uses. This code, which is the same as yours, except for indentation, works for me:

def f(i, v1):
v=[]
for j in v1:
v.append(j)
print(v)
v[i+1]=v1[i]
v[i]=v1[i+1]
return v

HTH

Justin

--
Justin C. Walker, Curmudgeon-At-Large
Institute for the Absorption of Federal Funds
--------
Men are from Earth.
Women are from Earth.
Deal with it.
--------

[jianrong]

Thank you very much!

[slelievre]

Simplifying the function and adding a docstring with an example:

def f(i, v1):

    r"""

    Return a copy of this list with elements of index `i` and `i + 1` swapped.

    EXAMPLE::

        sage: l = [5, 4, 3, 2, 1, 0]

        sage: f(3, l)

        [5, 4, 3, 1, 2, 0]

    """

    v = list(v1)

    v[i], v[i+1] = v[i+1], v[i]

    return v

Thanks to the docstring, one can now obtain the documentation

of the function with the usual question mark:

sage: f?

or the help function

sage: help(f)

[Daniel Krenn]

On 20.05.19 05:29, jianrong wrote:
> I am trying to write a function in sage to permute a list of elements.

An alternative might me something along the following:

|
Permutation("(1,2,3)(4,5)").action(['a', 'b', 'c', 'd', 'e'])
|