[issue40282] random.getrandbits(0) should succeed

[Antoine Pitrou]

Change by Antoine Pitrou :


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resolution:  -> fixed
stage: patch review -> resolved
status: open -> closed

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[issue40282] random.getrandbits(0) should succeed

[Antoine Pitrou]

Antoine Pitrou  added the comment:


New changeset 75a3378810bab03949ad9f653f78d933bdf3879c by Antoine Pitrou in 
branch 'master':
bpo-40282: Allow random.getrandbits(0) (GH-19539)
https://github.com/python/cpython/commit/75a3378810bab03949ad9f653f78d933bdf3879c


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[issue40282] random.getrandbits(0) should succeed

[Antoine Pitrou]

Change by Antoine Pitrou :


--
keywords: +patch
pull_requests: +18887
stage: needs patch -> patch review
pull_request: https://github.com/python/cpython/pull/19539

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[issue40282] random.getrandbits(0) should succeed

[STINNER Victor]

STINNER Victor  added the comment:

I created bpo-40286: Add getrandbytes() method to random.Random.

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[issue40282] random.getrandbits(0) should succeed

[STINNER Victor]

STINNER Victor  added the comment:

> That is feature creep and no user has requested it.

Python already provides such function in the secrets module, so I'm not sure if 
what you mean that "no users has requested it". secrets.token_bytes() exists 
because there is a need for such function.

secrets.token_bytes() is more designed for security, but random.Random() is 
more designed for simulations. And such users also exists, that's why numpy 
provides numpy.random.bytes(length) function:
https://docs.scipy.org/doc/numpy-1.15.0/reference/generated/numpy.random.bytes.html

To be honest, I never understood where there is such "hole" in the random 
module API. Especially for SystemRandom since its source os.urandom() generates 
bytes.

A concrete use case is to generate manually a UUID4 from 16 random bytes. For 
testing, you may want to get "deterministic random" UUID4. Using getrandbits() 
for thta sounds unnatural to me. 

Another use case is to create a secret token: well, that's basically that 
secrets.token_bytes() does. That's used in multiprocessing but also in urllib 
(AbstractDigestAuthHandler.get_cnonce()).

So yeah, it sounds perfectly reasonable to add such simple function. I don't 
see how add such obvious function would be a "feature creep".

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[issue40282] random.getrandbits(0) should succeed

[Antoine Pitrou]

Antoine Pitrou  added the comment:

I agree I don't *need* it per se.  However, I suspect that for non-exports it 
would be easier than
`getrandbits(nbytes * 8).to_bytes(nbytes, 'endian')`.

As for `secrets.token_bytes()`, it's not really adequate for regular 
pseudo-random data generation when you want to use a fixed seed.  And I'm not 
sure what its performance characteristics are when you pass a large size.

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[issue40282] random.getrandbits(0) should succeed

[Raymond Hettinger]

Raymond Hettinger  added the comment:

Why not use secrets.token_bytes() or randrange(2**b).to_bytes()?   Do you 
really need an API extension?

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nosy: +tim.peters

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[issue40282] random.getrandbits(0) should succeed

[Antoine Pitrou]

Change by Antoine Pitrou :


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components: +Library (Lib)

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[issue40282] random.getrandbits(0) should succeed

[Antoine Pitrou]

Change by Antoine Pitrou :


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stage:  -> needs patch

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[issue40282] random.getrandbits(0) should succeed

[Antoine Pitrou]

Antoine Pitrou  added the comment:

About a hypothetical getrandbytes(), probably 90% of my uses of getrandbits() 
have been to generate random bytestrings.

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[issue40282] random.getrandbits(0) should succeed

[Serhiy Storchaka]

Serhiy Storchaka  added the comment:

I do not want to open an issue if I know that the idea will be rejected.

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[issue40282] random.getrandbits(0) should succeed

[Raymond Hettinger]

Raymond Hettinger  added the comment:

+0 for having getrandbits(0) return 0.  Conceptually, it is reasonable.  
Practically, it is a bit inconvenient because the ValueError may have to be 
moved upstream to the _randbelow() methods.

-1 for getrandbytes().  That is feature creep and no user has requested it.  
Also, the name leads to a confusing API with getrandbits() returning arbitrary 
sized python ints and getrandbytes() returning bytes.  Lastly, it mostly 
duplicates functionality already supplied by secrets.token_bytes().  If you 
really want this, open another tracker issue and don't derail the issue at hand.

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[issue40282] random.getrandbits(0) should succeed

[Mark Dickinson]

Mark Dickinson  added the comment:

This was discussed previously in #37000.

I agree that `getrandbits(0)` should succeed.

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[issue40282] random.getrandbits(0) should succeed

[Serhiy Storchaka]

Serhiy Storchaka  added the comment:

Seconded.

And I wish to add the getrandbytes() method.

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nosy: +serhiy.storchaka

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[issue40282] random.getrandbits(0) should succeed

[Antoine Pitrou]

Antoine Pitrou  added the comment:

I think you know the answer to your question ;-)

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[issue40282] random.getrandbits(0) should succeed

[STINNER Victor]

STINNER Victor  added the comment:

How random would be the 0 returned by getrandbits(0)? :-)

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[issue40282] random.getrandbits(0) should succeed

[Antoine Pitrou]

New submission from Antoine Pitrou :

When creating variable-sized random binary strings with random.getrandbits(), 
you currently have to special case when the number of bytes is 0, because 
otherwise getrandbits() raises:

  ValueError: number of bits must be greater than zero

It seems like it wouldn't hurt to simply return 0 in that case.

The actual snippet looks something like:

  random.getrandombits(nbytes * 8).to_bytes(nbytes, 'little')

--
messages: 366392
nosy: mark.dickinson, pitrou, rhettinger, steven.daprano
priority: normal
severity: normal
status: open
title: random.getrandbits(0) should succeed
type: enhancement
versions: Python 3.9

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