Python Language Concatenate and Merge lists


Example

  1. The simplest way to concatenate list1 and list2:

    merged = list1 + list2
    
  2. 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
    
  1. 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']