How to Switch Position of Two Items in a Python List

How to switch position of two items in a Python list?

i = ['title', 'email', 'password2', 'password1', 'first_name', 
     'last_name', 'next', 'newsletter']
a, b = i.index('password2'), i.index('password1')
i[b], i[a] = i[a], i[b]

How can I swap two elements in one array?

#a=np.array([2,7]) 
a=[2,7]

# Reversing a list using slice notation
print (a[::-1]) # [7, 2]

# The reversed() method
print (list(reversed(a))) # [7, 2]

swap two elements in a list:

# Swap function
def swapPositions(list, pos1, pos2):
    list[pos1], list[pos2] = list[pos2], list[pos1]
    return list

a=[2,7]
pos1, pos2 = 0, 1

print(swapPositions(a, pos1 - 1, pos2 - 1))

Swap elements within a list

You can swap tuples in one step with:

def swap(x, y):
     mylist[x], mylist[y] = mylist[y], mylist[x]

mylist = ["a", "b", "c", "d"]

swap(2, 3)
print(mylist)
# ['a', 'b', 'd', 'c']

Better way to swap elements in a list?

No need for complicated logic, simply rearrange the list with slicing and step:

In [1]: l = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]

In [2]: l[::2], l[1::2] = l[1::2], l[::2]

In [3]: l
Out[3]: [2, 1, 4, 3, 6, 5, 8, 7, 10, 9]

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 TLDR;

Edited with explanation

I believe most viewers are already familiar with list slicing and multiple assignment. In case you don't I will try my best to explain what's going on (hope I do not make it worse).

To understand list slicing, here already has an excellent answer and explanation of list slice notation.
Simply put:

a[start:end] # items start through end-1
a[start:]    # items start through the rest of the array
a[:end]      # items from the beginning through end-1
a[:]         # a copy of the whole array

There is also the step value, which can be used with any of the above:

a[start:end:step] # start through not past end, by step

Let's look at OP's requirements:

 [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]  # list l
  ^  ^  ^  ^  ^  ^  ^  ^  ^  ^
  0  1  2  3  4  5  6  7  8  9    # respective index of the elements
l[0]  l[2]  l[4]  l[6]  l[8]      # first tier : start=0, step=2
   l[1]  l[3]  l[5]  l[7]  l[9]   # second tier: start=1, step=2
-----------------------------------------------------------------------
l[1]  l[3]  l[5]  l[7]  l[9]
   l[0]  l[2]  l[4]  l[6]  l[8]   # desired output

First tier will be: l[::2] = [1, 3, 5, 7, 9]
Second tier will be: l[1::2] = [2, 4, 6, 8, 10]

As we want to re-assign first = second & second = first, we can use multiple assignment, and update the original list in place:

first , second  = second , first

that is:

l[::2], l[1::2] = l[1::2], l[::2]

As a side note, to get a new list but not altering original l, we can assign a new list from l, and perform above, that is:

n = l[:]  # assign n as a copy of l (without [:], n still points to l)
n[::2], n[1::2] = n[1::2], n[::2]

Hopefully I do not confuse any of you with this added explanation. If it does, please help update mine and make it better :-)

Python: change elements position in a list of instances

First, I didn't get the error you mentioned.

Second, it seems that you made a mistake in using insert, should be insert(1, c) rather than insert(c, 1), see docs

>>> d = [[1, 2], [5, 6], [3, 4]]
>>> c = d[1]
>>> d.remove(c)
>>> d
[[1, 2], [3, 4]]
>>> d.insert(c, 1)
Traceback (most recent call last):
  File "<pyshell#16>", line 1, in <module>
    d.insert(c, 1)
TypeError: 'list' object cannot be interpreted as an integer
>>> d.insert(1, c)
>>> d
[[1, 2], [5, 6], [3, 4]]

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