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Re: code to initialize a sequence

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From: __pete...@web.de (Peter Otten)
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Subject: Re: code to initialize a sequence
Date: Sun, 29 Aug 2021 21:15:03 +0200
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by: Peter Otten - Sun, 29 Aug 2021 19:15 UTC

On 29/08/2021 20:44, joseph pareti wrote:
> In the code attached below, the A-variant is from somebody else who knows
> Python better than I. But I do not like to just use any code without having
> a grasp, specifically the line in* bold*, so I wrote the B-variant which
> gives the same results. The C-variant is identical to A and is there for
> verification: after resetting the seed I expect the same sequence. The
> D-variant is closer to the way I code, and it does not work.

So you do you want us to debug the _EXPLICIT version?
The assignment

> X[i] = [randint(0, n_unique-1)]

creates a list with one element and turns it into an item in the list X.
You don't want a list, you want the numerical value, the
straight-forward way to achieve that being

X[i] = randint(0, n_unique-1)

An alternative is to assign to a slice

X[i:i+1] = [randint(...)]

but that would only make sense if the right-hand-side list weren't
created in the line and ditched immediately afterwards.

>
>
> import random
> from random import randint, seed
>
> def generate_sequence(length, n_unique):
> *return [randint(0, n_unique-1) for k in range(length)]*

The above is the most pythonic of the three versions. Once you
understand how for loops with a list.append() are turned into
comprehensions it will be easy to write and read that style. Definitely
worth learning and adopting.

>
> def generate_sequence_JP(length, n_unique):
> LI = []
> for k in range(length):
> LI.append(randint(0, n_unique-1))
> return(LI)

This is also fine and often used when the loop body is a bit more
complex, but

> def generate_sequence_EXPLICIT(length, n_unique):
> X =[None] * length
> for i in range(length):
> X[i] = [randint(0, n_unique-1)]
> return X

this is garbage even when it works, usually indicative of premature
optimization.

Random (yeah!) remark: Python uses half-open intervals (i. e. intervals
that include the lower bound, but not the upper bound) almost
everywhere. randint() is one exception.
Personally I prefer its conformist sister randrange(); with that
randint(0, n_unique-1)
becomes
randrange(n_unique)

> #
> # MAIN PROGRAM
> #
> random.seed(2)
> A = generate_sequence(4, 10 )
> random.seed(2)
> B = generate_sequence_JP(4, 10)
> random.seed(2)
> C = generate_sequence(4, 10 )
> random.seed(2)
> D = generate_sequence_EXPLICIT(4, 10 )
> print(A)
> print(type(A))
> print('-----------------------------')
> print(B)
> print(type(B))
> print('-----------------------------')
> print(C)
> print(type(C))
> print('-----------------------------')
> print(D)
> print(type(D))
>
>
> Regards,
> Joseph Pareti - Artificial Intelligence consultant
> Joseph Pareti's AI Consulting Services
> https://www.joepareti54-ai.com/
> cell +49 1520 1600 209
> cell +39 339 797 0644
>

Subject	Author
Re: code to initialize a sequence	Peter Otten