How To Set Size Of List In Python

Python Tutorials

Python: Initialize List of Size N

You cannot assign items to a listing at positions that exercise not exist. This is because lists are indexed from zero and new index positions increment by one each time an item is added to a list.

This means if you lot want to add items to a particular position in a listing, there needs to exist a placeholder value in that position.

In this guide, we talk over how to initialize a listing of size n in Python. We walk through an instance of how to do this so yous can initialize lists with custom sizes in your programs.

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Python: Initialize List of Size N Using Multiplication

We're going to build a leaderboard application that tracks the positions of the winners of a math tournament. This leaderboard will brandish the concluding eight students in the tournament.

Students are added in descending society. This is considering the first pupil in the list is the winner and the 8th pupil is in the 8th identify.

To start, create an empty listing in Python :

leaderboard = [None] * viii print(leaderboard)

This code creates a list object with eight values. Each of the values in the list will be equal to None.

Our code returns our list of None values:

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[None, None, None, None, None, None, None, None]

The value None could be substituted with whatsoever default value that yous desire. For instance, you could make each default value an empty string (""), the number zero (0), or something else.

The quarter-final has but completed and two contestants have been eliminated. The following contestants can now be added to our leaderboard:

Chad (seventh place)
Eileen (eighth place)

To add together these students to our list, nosotros use the consignment note :

leaderboard[7] = "Eileen" leaderboard[vi] = "Chad"

We set the value of the particular at position 7 to Eileen and the value at position vi to Chad. This is because lists are indexed from nada. The offset item in our list has the value 0 and the last item has the value 7. This means Eileen is last in our list and Republic of chad is second from terminal.

Next, let's write a "for" loop that displays all the positions in our leaderboard and the people who currently hold that position:

for l in range(0, len(leaderboard)): 		 if leaderboard[l] != None: 		         value = leaderboard[fifty] 	     else: 		         value = "TBD"  	     print("{}: {}".format(l + one, value))

We use a range() statement to create a list of values between 0 and the length of the "leaderboard" list. This lets united states of america iterate over our list of students in the leaderboard while keeping track of each position.

In our loop, nosotros cheque if the value at a particular position in the list is equal to None . If information technology is not, the value at that position is assigned to the variable "value". Otherwise, the value "TBD" is assigned to the variable "value".

Next, we print out the value of the "value" variable. We also impress out the value of "l" plus i. This is because lists are indexed from aught and to evidence a rank we should add one to that value. Otherwise, our leaderboard would start from naught.

Let'south run our code and see what happens:

[None, None, None, None, None, None, None, None] one: TBD two: TBD 3: TBD 4: TBD v: TBD half-dozen: TBD 7: Chad 8: Eileen

Our code first prints out a list of None values. Next, our code assigns values to the concluding two items in our list. Finally, our code prints out the positions in our leaderboard.

Python: Initialize List of Size N Using range()

We can initialize a listing of size n using a range() statement. The difference betwixt using a range() statement and the None method is that a range() argument will create a list of values between two numbers. By default, range() creates a list from 0 to a particular value.

Let's initialize our leaderboard list using a range() statement:

leaderboard = list(range(8)) print(leaderboard)

The range() statement creates a sequence of values between 0 and 7. We convert that sequence into a listing so we can iterate over it. This is only necessary in Python 3.

Our lawmaking returns a new listing with viii values:

Conclusion

You can initialize a list of a custom size using either multiplication or a range() statement.

The multiplication method is best if you want to initialize a list with the same values. A range() argument is a good choice if you lot want a list to contain values in a particular range.

Now you lot have the skills you need to initialize a Python list of size n like an good!

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James Gallagher

Nearly the writer: James Gallagher is a cocky-taught programmer and the technical content managing director at Career Karma. He has experience in range of programming languages and extensive expertise in Python, HTML, CSS, and JavaScript. James has written hundreds of programming tutorials, and he frequently contributes to publications like Codecademy, Treehouse, Repl.it, Afrotech, and others. He also serves as a researcher at Career Karma, publishing comprehensive reports on the bootcamp market.

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