Python Language Tutorial => Concatenate and Merge lists

Example

The simplest way to concatenate list1 and list2:
```
merged = list1 + list2
```

zip returns a list of tuples, where the i-th tuple contains the i-th element from each of the argument sequences or iterables:

alist = ['a1', 'a2', 'a3']
blist = ['b1', 'b2', 'b3']

for a, b in zip(alist, blist):
    print(a, b)
 
# Output:
# a1 b1
# a2 b2
# a3 b3

If the lists have different lengths then the result will include only as many elements as the shortest one:

alist = ['a1', 'a2', 'a3']
blist = ['b1', 'b2', 'b3', 'b4']
for a, b in zip(alist, blist):
    print(a, b)

# Output:
# a1 b1
# a2 b2
# a3 b3

alist = []
len(list(zip(alist, blist)))

# Output:
# 0

For padding lists of unequal length to the longest one with Nones use itertools.zip_longest (itertools.izip_longest in Python 2)

alist = ['a1', 'a2', 'a3']
blist = ['b1']
clist = ['c1', 'c2', 'c3', 'c4']

for a,b,c in itertools.zip_longest(alist, blist, clist):
    print(a, b, c)

# Output: 
# a1 b1 c1
# a2 None c2
# a3 None c3
# None None c4

Insert to a specific index values:

 alist = [123, 'xyz', 'zara', 'abc']
 alist.insert(3, [2009])
 print("Final List :", alist)

Output:

 Final List : [123, 'xyz', 'zara', 2009, 'abc']

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