Initialise a list to a specific length in Python

Considerations of list multiplication

When initializing a list with [value] * n, value is repeated to fill the list to n elements. This method is highly efficient for immutable objects like integers or strings, but can lead to quirky results with mutable objects like lists or dictionaries, where all elements point to the same reference.

Utilizing list comprehension for mutable objects

For mutable default values, you can start practicing your yoga skills with list comprehension:

# Initializing a list with ten unique dictionaries, Snowflake style
my_list = [{} for _ in range(10)]
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This small puzzle ensures each dictionary is a unique snowflake no matter how hard you squash them together. So, remember your list comprehension - it's not just smart, but it's also social distancing approved!.

Pre-allocation: The crystal ball of lists

Pre-allocating a list's size with [None] * n is an efficient way to say: "I know exactly what I'm doing". For more "aha moments", check out Raymond Hettinger’s PyCon talks. They are the "Bob Ross painting" of Python concepts.

Extra flavor with itertools

Sure, [None] * n is like vanilla ice cream - everyone's safe choice. But sometimes, you need to spice things up with a bit of itertools:

import itertools

# Create a list of 10 Nones, because variety is overrated
my_list = list(itertools.repeat(None, 10))
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This code does the same job, but adds a bit of sprinkles to your vanilla ice cream when you need an iterator instead of a list.

Striking balance with efficiency

List initialization with multiplication is as memory-friendly as a well-trained puppy. But creating a large list of mutable objects on-the-fly doesn't feel right, consider using a generator expressions or itertools.repeat to streamline the process, just like a sushi chef!

Mutable gotchas

You might get a brainwave and try [[]] * 10. But beware! This command is a Pandora's box and creates ten identical items. You'd better do:

my_list = [[] for _ in range(10)]  # Here, ten individual snowflakes
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This ensures ten different snowflakes... I mean lists, each quirky in its own way.