Python: Processing lists in reverse order

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Python: Processing lists in reverse order

by RS admin@ycp.powersoftwo.org

1. Python: Processing lists in reverse order

There are many ways to process a Python list in reverse order. Consider the following list.

list1 = ["one", "two", "three", "four", "five"]

The code examples will output this list in reverse order. The code examples create a new list2 that is the list list1 reversed. Output is done in the same way.

text2 = " ".join(list2)
print("{0:s}".format(text2))

2. Make a new list

This way makes a new list by traversing the list in reverse order. This is not the best way to do this.

Here is the Python code.

list1 = ["one", "two", "three", "four", "five"]
list2 = []
for pos1 in range(len(list1)-1,-1,-1):
	item1 = list1[pos1]
	list2.append(item1)
text2 = " ".join(list2)
print("{0:s}".format(text2))

Here is the output of the Python code.

five four three two one

3. List comprehension

Another way is to reverse the original list to a new list using a list comprehension.

Here is the Python code.

list1 = ["one", "two", "three", "four", "five"]
list2 = list1[::-1]
text2 = " ".join(list2)
print("{0:s}".format(text2))

Here is the output of the Python code.

five four three two one

One can directly print the list using a list comprehension.

Here is the Python code.

list1 = ["one", "two", "three", "four", "five"]
list2 = [s1 for s1 in list1[::-1]]
text2 = " ".join(list2)
print("{0:s}".format(text2))

Here is the output of the Python code.

five four three two one

4. Reversed

There is a reversed function that can do this efficiently.

Here is the Python code.

list1 = ["one", "two", "three", "four", "five"]
list2 = reversed(list1)
text2 = " ".join(list2)
print("{0:s}".format(text2))

Here is the output of the Python code.

five four three two one

5. Combining everything

Here is a short way to do this.

Here is the Python code.

list1 = ["one", "two", "three", "four", "five"]
print(" ".join(reversed(list1)))

Here is the output of the Python code.

five four three two one

6. End of page

by RS admin@ycp.powersoftwo.org