How to restrict the number of elements in python lists

Question

I came from C world where the size of buffers can be controlled in advance. For instance, declaring a buffer of doubles that holds 10 elements, we do:

double *buffer = calloc(10, sizeof(double));

In Python, it is quite the contrary in the sense that we don't need to worry about the details and the size of the buffer by saying buffer=[].

My question is: If I want to restrict a python list to hold an arbitrary number of values, say 10 doubles, how can we do that with default python lists or maybe numpy?

I don't think this is a precise duplicate as user is open to numpy. — jpp
– jpp, Commented Apr 18, 2018 at 21:00
I fail to see how this is a duplicate of the linked question. Initializing to a length and actually restricting the length are not the same thing. — Paul Panzer
– Paul Panzer, Commented Apr 18, 2018 at 21:28
@jpp I added another to the dupe list with the same C foreword even. — miradulo
– miradulo, Commented Apr 18, 2018 at 21:28
@PaulPanzer Did you see the second duplicate in the list there? — miradulo
– miradulo, Commented Apr 18, 2018 at 21:29

jpp · Accepted Answer · 2018-04-18 21:00:13Z

2

To ensure an array is of a fixed size and of a certain type, you should use numpy. This is true even with non-numeric data.

Some examples are below.

import numpy as np

arr = np.zeros(10, dtype=float)
# array([ 0.,  0.,  0.,  0.,  0.,  0.,  0.,  0.,  0.,  0.]), dtype = float64

arr = np.zeros(10, dtype=int)
# array([0, 0, 0, 0, 0, 0, 0, 0, 0, 0]), dtype = int32

arr = np.empty(10, dtype='<U8')
# array(['', '', '', '', '', '', '', '', '', ''],
#       dtype='<U8')

answered Apr 18, 2018 at 21:00

jpp

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Tyler K · Accepted Answer · 2018-04-18 20:58:43Z

1

You can use deque from collections that has a maxlen property.

from collections import deque
d = deque(maxlen=2)

You can then append, pop, iterate or do whatever you want with your restricted list.

answered Apr 18, 2018 at 20:58

Tyler K

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