Lesson 12 of 21 · about 6 minutes with the exercises

Sorting, slicing and searching lists

The last lesson built and changed lists. This one is about putting them in order, cutting pieces from them and finding things in them.

Sorting

There are two ways to sort, and the difference matters.

marks = [78, 45, 91, 60]
marks.sort()
print(marks)

names = ["Ravi", "Asha", "Meena"]
ordered = sorted(names)
print(ordered)
print(names)

[45, 60, 78, 91]
['Asha', 'Meena', 'Ravi']
['Ravi', 'Asha', 'Meena']

• The method list.sort() rearranges the list itself and returns nothing.
• The function sorted(list) leaves the original alone and returns a new sorted list.

Use sorted when you still need the original order. Use .sort() when you do not.

For largest first, add reverse=True.

marks = [78, 45, 91, 60]
marks.sort(reverse=True)
print(marks)
print(sorted(["pear", "apple", "fig"], reverse=True))

[91, 78, 60, 45]
['pear', 'fig', 'apple']

Text is sorted alphabetically, but capital letters come before all small letters. To ignore case, pass key=str.lower. A key is a function that Python applies to each item just for the comparison.

words = ["banana", "Apple", "cherry"]
print(sorted(words))
print(sorted(words, key=str.lower))
print(sorted(words, key=len))

['Apple', 'banana', 'cherry']
['Apple', 'banana', 'cherry']
['Apple', 'banana', 'cherry']

The last line sorts by length, shortest first.

Reversing

order = [1, 2, 3, 4]
order.reverse()
print(order)
print(order[::-1])

[4, 3, 2, 1]
[1, 2, 3, 4]

reverse turns the list around in place. The slice [::-1] gives a reversed copy.

Slices

Slicing a list works like slicing a string and always gives a new list.

days = ["Mon", "Tue", "Wed", "Thu", "Fri", "Sat", "Sun"]
print(days[:5])
print(days[5:])
print(days[1:4])
print(days[::2])
print(days[-3:])

['Mon', 'Tue', 'Wed', 'Thu', 'Fri']
['Sat', 'Sun']
['Tue', 'Wed', 'Thu']
['Mon', 'Wed', 'Fri', 'Sun']
['Fri', 'Sat', 'Sun']

days[:5] is the first five items. days[-3:] is the last three. These two are worth remembering: top five and bottom three of a sorted list are one slice each.

scores = [55, 92, 71, 88, 64, 97]
top3 = sorted(scores, reverse=True)[:3]
print(top3)

[97, 92, 88]

Finding things

names = ["Asha", "Ravi", "Meena", "Ravi"]
print("Meena" in names)
print("Kabir" not in names)
print(names.index("Ravi"))
print(names.count("Ravi"))

True
True
1
2

in answers yes or no. index gives the position of the first match. count says how many times a value appears. index raises an error if the value is missing, so check with in first when you are not sure.

Smallest, largest, average

temps = [31, 29, 35, 33, 30]
print(min(temps), max(temps))
print(sum(temps) / len(temps))
print(temps.index(max(temps)))

29 35
31.6
2

The last line finds where the hottest day sits in the list.

Two lists side by side

zip pairs up the items of two lists, first with first, second with second.

names = ["Asha", "Ravi", "Meena"]
marks = [78, 91, 66]
for name, mark in zip(names, marks):
    print(f"{name:<6}{mark}")

Asha  78
Ravi  91
Meena 66

If one list is longer, zip stops at the end of the shorter one.

Joining and repeating lists

a = [1, 2]
b = [3, 4]
print(a + b)
print(a * 3)
print([0] * 5)

[1, 2, 3, 4]
[1, 2, 1, 2, 1, 2]
[0, 0, 0, 0, 0]

[0] * 5 is a quick way to make a list of five zeros to fill in later.

From text to list and back

split and join from the string lesson are the bridge between text and lists.

line = "tea, coffee, lassi"
drinks = line.split(", ")
drinks.sort()
print(drinks)
print(" | ".join(drinks))

['coffee', 'lassi', 'tea']
coffee | lassi | tea

To turn a string of numbers into real numbers, convert each piece.

text = "12 7 30"
numbers = []
for piece in text.split():
    numbers.append(int(piece))
print(numbers, sum(numbers))

[12, 7, 30] 49

Common mistakes

• Writing marks = marks.sort(). The method returns None, so the list is lost. Write marks.sort() on its own line.
• Sorting a list that mixes numbers and text. Python cannot compare the two and stops with a TypeError.
• Expecting a slice to change the original list. It makes a copy.

Try it yourself

prices = [250, 99, 480, 150, 320]
print(sorted(prices)[:2])

[99, 150]

names = ["meena", "Asha", "ravi"]
print(sorted(names, key=str.lower))

['Asha', 'meena', 'ravi']

items = ["pen", "book", "bag"]
qty = [10, 4, 1]
for item, q in zip(items, qty):
    print(item, q)

pen 10
book 4
bag 1

Mark this lesson as done

Examples on this page were run with Python 3.14 on 12 November 2026. The output shown is the real output.

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