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I can perform
a = [1,2,3] b = [4,5,6] a.extend(b) # a is now [1,2,3,4,5,6] Is there way to perform an action for extending list and adding new items to the beginning of the list?
Like this
a = [1,2,3] b = [4,5,6] a.someaction(b) # a is now [4,5,6,1,2,3] I use version 2.7.5, if it is important.
755
To prepend to a list in Python, use the list. insert() method with index set to 0, which adds an element at the beginning of the list. The insert() is a built-in Python function that inserts an item to the list at the given index.
append() adds a single element to the end of the list while . extend() can add multiple individual elements to the end of the list.
When append() method adds its argument as a single element to the end of a list, the length of the list itself will increase by one. Whereas extend() method iterates over its argument adding each element to the list, extending the list.
You can assign to a slice:
a[:0] = b Demo:
>>> a = [1,2,3] >>> b = [4,5,6] >>> a[:0] = b >>> a [4, 5, 6, 1, 2, 3] Essentially, list.extend() is an assignment to the list[len(list):] slice.
You can 'insert' another list at any position, just address the empty slice at that location:
>>> a = [1,2,3] >>> b = [4,5,6] >>> a[1:1] = b >>> a [1, 4, 5, 6, 2, 3] This is what you need ;-)
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