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Some sample programs

Replacing a slice

You can replace a slice in a list with the elements from another list through assignment.

Can change the length of the list

Note that this operation can change the length of the original list.

The script in Listing 1 replaces a slice in a list with the elements from another list.

Listing 1 . Replace a slice in a list.
# Illustrates replacing a slice in a list ##---------------------------------------- print("Create and print a list")listA = [100,200,300,400,500] print(listA)print("Original length is:") print(len(listA))print("Replace a slice") listA[1:4]= [2,4,8,16,32,64] print("Print the modified list")print(listA) print("Modified length is:")print(len(listA))

The function named len()

This program also illustrates the use of the function named len() to get and print the length of the list.

Replaces a three-element slice with a six-element list

In this program, a slice of an original five-element list, consisting of the elements from 1 through 3 inclusive, is replaced by the elements of a new listconsisting of six new elements.

Length of the list is increased by 3

Since three existing elements are replaced by six new elements, the overall length of the listis increased by three elements.

Program output

The output from this program is shown in Figure 1 .

Figure 1 . Program output.
Create and print a list [100, 200, 300, 400, 500]Original length is: 5Replace a slice Print the modified list[100, 2, 4, 8, 16, 32, 64, 500] Modified length is:8

As you can see in Figure 1 , the six new elements replaced the three original elements to increase the length of the list from 5 to 8 elements.

Replacing an element with a list

It is also possible to replace an element in an existing list with a new list, as illustrated by the program in Listing 2 .

Behavior is different from above

In this case, the behavior is different from that shown above where a slice from the original list was replaced with the elements from a different list (even though the right operand of the assignment operator is the same in both cases) .

Produces nested lists

When a single element is replaced by a list, the result is that a new list is nested inside the original list .

Length is unchanged

It is also interesting to note that the length of the list is unchanged by this operation since the list that replaces the element is itself considered tobe a single element. Therefore, the number of elements is not changed.

This is illustrated in Listing 2 , where the element at index 2 of an original list is replaced with a new listhaving six elements.

Listing 2 . Replacing an element with a list.
# Illustrates replacing an # element with a slice# #-------------------------------print("Create and print a list") listA = [100,200,300,400,500]print(listA) print("Original length is:")print(len(listA)) print("Replace an element")listA[2] = [2,4,8,16,32,64]print("Print the modified list") print(listA)print("Modified length is:") print(len(listA))

Program output from replacing an element with a list

The output from this program is shown in Figure 2 .

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Source:  OpenStax, Itse 1359 introduction to scripting languages: python. OpenStax CNX. Jan 22, 2016 Download for free at https://legacy.cnx.org/content/col11713/1.32
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