[issue37150] Do not allow to pass FileType class object instead of instance in add_argument

[Andrew Svetlov]

Change by Andrew Svetlov :


--
resolution:  -> fixed
stage: patch review -> resolved
status: open -> closed
versions:  -Python 2.7, Python 3.7

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[issue37150] Do not allow to pass FileType class object instead of instance in add_argument

[miss-islington]

miss-islington  added the comment:


New changeset 606ac581e2451c420117c55632f0fe13d4cec2cd by Miss Islington (bot) 
in branch '3.8':
bpo-37150: Throw ValueError if FileType class object was passed in add_argument 
(GH-13805)
https://github.com/python/cpython/commit/606ac581e2451c420117c55632f0fe13d4cec2cd


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[issue37150] Do not allow to pass FileType class object instead of instance in add_argument

[miss-islington]

Change by miss-islington :


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pull_requests: +13776
pull_request: https://github.com/python/cpython/pull/13901

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[issue37150] Do not allow to pass FileType class object instead of instance in add_argument

[miss-islington]

miss-islington  added the comment:


New changeset 03d5831a2d62c68654ec223168e574cd546efbf6 by Miss Islington (bot) 
(zygocephalus) in branch 'master':
bpo-37150: Throw ValueError if FileType class object was passed in add_argument 
(GH-13805)
https://github.com/python/cpython/commit/03d5831a2d62c68654ec223168e574cd546efbf6


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nosy: +miss-islington

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[issue37150] Do not allow to pass FileType class object instead of instance in add_argument

[Michele Angrisano]

Change by Michele Angrisano :


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nosy: +bethard

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[issue37150] Do not allow to pass FileType class object instead of instance in add_argument

[Demid]

Demid  added the comment:

What if I will add mode check in FileType.__init__?

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[issue37150] Do not allow to pass FileType class object instead of instance in add_argument

[Josh Rosenberg]

Josh Rosenberg  added the comment:

Ah, right. It doesn't actually validate the mode string (it just stores it for 
when open is called, assuming open will validate it). So yeah, it silently 
accepts any string, not just valid mode strings. Not a contractual guarantee or 
anything, just how FileType.__init__ is implemented.

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[issue37150] Do not allow to pass FileType class object instead of instance in add_argument

[Demid]

Demid  added the comment:

If you will run `python test.py hello.txt, where test.py is:

import argparse

parser = argparse.ArgumentParser()
parser.add_argument('echo', type=argparse.FileType)
args = parser.parse_args()
print(args.echo)

You will receive:
FileType('hello.txt')

I think that can be confusing for someone who will forget to invoke FileType 
constructor.

‐‐‐ Original Message ‐‐‐
On Tuesday, June 4, 2019 10:27 PM, Michele Angrisano  
wrote:

>
>
> Michele angrisanomichele.angris...@gmail.com added the comment:
>
> Reading the examples in the doc, it's clear the behavior when FileType takes 
> an argument. What's the behavior of FileType when is called without any 
> argument?
>
> -
>
> nosy: +mangrisano
>
> Python tracker rep...@bugs.python.org
> https://bugs.python.org/issue37150

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[issue37150] Do not allow to pass FileType class object instead of instance in add_argument

[Michele Angrisano]

Michele Angrisano  added the comment:

Yes, I meant that. Thanks! :)

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[issue37150] Do not allow to pass FileType class object instead of instance in add_argument

[Josh Rosenberg]

Josh Rosenberg  added the comment:

The docs specify what argparse.FileType() does via the default parameters: 
https://docs.python.org/3/library/argparse.html#argparse.FileType

If you mean what does it do when you fail to call it at all (passing 
type=argparse.FileType), the answer is the same as any other class: It tries to 
construct a FileType using the user provided argument as the sole positional 
argument. So if the user passes a valid mode string, it works, and returns a 
FileType object with that mode string, otherwise it barfs and dumps an error 
message for passing an invalid argument for FileType.

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nosy: +josh.r

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[issue37150] Do not allow to pass FileType class object instead of instance in add_argument

[Michele Angrisano]

Michele Angrisano  added the comment:

Reading the examples in the doc, it's clear the behavior when FileType takes an 
argument. What's the behavior of FileType when is called without any argument?

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nosy: +mangrisano

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[issue37150] Do not allow to pass FileType class object instead of instance in add_argument

[paul j3]

paul j3  added the comment:

I don't see an easy way around this.  FileType is a class, and thus is a 
callable.  add_argument checks that the 'type' parameter is a callable (or a 
string in the registry).  Otherwise it gives the programmer a lot of freedom 
regarding this parameter.

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[issue37150] Do not allow to pass FileType class object instead of instance in add_argument

[Karthikeyan Singaravelan]

Change by Karthikeyan Singaravelan :


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nosy: +paul.j3

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[issue37150] Do not allow to pass FileType class object instead of instance in add_argument

[SilentGhost]

Change by SilentGhost :


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versions:  -Python 3.5, Python 3.6

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[issue37150] Do not allow to pass FileType class object instead of instance in add_argument

[Demid]

Change by Demid :


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keywords: +patch
pull_requests: +13690
stage:  -> patch review
pull_request: https://github.com/python/cpython/pull/13805

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[issue37150] Do not allow to pass FileType class object instead of instance in add_argument

[Demid]

New submission from Demid :

There is a possibility that someone (like me) accidentally will omit 
parentheses with FileType arguments after FileType, and parser will contain 
wrong file until someone will try to use it. 

Example:
parser = argparse.ArgumentParser()
parser.add_argument('-x', type=argparse.FileType)

--
components: Library (Lib)
messages: 344568
nosy: zygocephalus
priority: normal
severity: normal
status: open
title: Do not allow to pass FileType class object instead of instance in 
add_argument
type: enhancement
versions: Python 2.7, Python 3.5, Python 3.6, Python 3.7, Python 3.8, Python 3.9

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