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mimetypes.guess_type could not find mimetypes added by mimetypes.add_type i.e. in PY3.10.4 // OR : different return values (PY2.7 to PY3.9.7) vs (PY3.9.11 to PY3.10.4) #92455

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ifrh opened this issue May 8, 2022 · 2 comments
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mimetypes.guess_type could not find mimetypes added by mimetypes.add_type i.e. in PY3.10.4 // OR : different return values (PY2.7 to PY3.9.7) vs (PY3.9.11 to PY3.10.4) #92455

ifrh opened this issue May 8, 2022 · 2 comments
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stdlib Python modules in the Lib dir type-bug An unexpected behavior, bug, or error

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@ifrh
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ifrh commented May 8, 2022 •
edited by hugovk
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I think something is broken in mimetype.guess_type or documentation did not cover the change ...

A small working example and its outputs for different Python versions are listed below.
In this example the value from a concrete mimetypes.types_map entry should
match to the returnvalue of mimetypes.guess_type in all tested Python versions:
But it did not; the return value of mimetypes.guess_type is wrong from my point of view.

Operating system and architecture:
Windows 10/WSL

$ uname -s -v -i -m -p -o
Linux #1237-Microsoft Sat Sep 11 14:32:00 PST 2021 x86_64 x86_64 x86_64 GNU/Linux

Ubuntu

$ uname -s -v -i -m -p -o
Linux #220-Ubuntu SMP Thu May 9 12:40:49 UTC 2019 x86_64 x86_64 x86_64 GNU/Linux

Small working example : mimetest.py

import mimetypes
mimetypes.init()
MIMETYPE_ADDITIONAL_EXTENSIONS = [("text/x-r-script", ".R"), ]
for (mimetype, extension) in MIMETYPE_ADDITIONAL_EXTENSIONS:
    mimetypes.add_type(mimetype, extension, strict=True)
print("mimetypes.types_map['.R'] = %s , mimetypes.guess_type('example.R')[0] = %s" % (mimetypes.types_map['.R'],mimetypes.guess_type('example.R')[0]))

Running this via multiple Python versions is showing the problem:

Python 2.7.17
mimetypes.types_map['.R'] = text/x-r-script , mimetypes.guess_type('example.R')[0] = text/x-r-script
Python 3.5.6
mimetypes.types_map['.R'] = text/x-r-script , mimetypes.guess_type('example.R')[0] = text/x-r-script
Python 3.6.13
mimetypes.types_map['.R'] = text/x-r-script , mimetypes.guess_type('example.R')[0] = text/x-r-script
Python 3.9.7
mimetypes.types_map['.R'] = text/x-r-script , mimetypes.guess_type('example.R')[0] = text/x-r-script
Python 3.9.11
mimetypes.types_map['.R'] = text/x-r-script , mimetypes.guess_type('example.R')[0] = None
Python 3.9.12
mimetypes.types_map['.R'] = text/x-r-script , mimetypes.guess_type('example.R')[0] = None
Python 3.10.4
mimetypes.types_map['.R'] = text/x-r-script , mimetypes.guess_type('example.R')[0] = None

perhaps this different behavior is a result of issue #64591
and its related merged pull requests
@ifrh ifrh added the type-bug An unexpected behavior, bug, or error label May 8, 2022
@ifrh ifrh mentioned this issue May 8, 2022
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@ifrh
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ifrh commented May 8, 2022 •
edited by hugovk
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old implementation

cpython/Lib/mimetypes.py

Lines 146 to 149 in 64a68c3

if ext in types_map:
return types_map[ext], encoding
elif ext.lower() in types_map:
return types_map[ext.lower()], encoding

current implementation

cpython/Lib/mimetypes.py

Lines 146 to 149 in 4802344

ext = ext.lower()
types_map = self.types_map[True]
if ext in types_map:
return types_map[ext], encoding

changing my small example adding both extensions ".r" and ".R" via mimetypes.add_type gives

$ python ./mimetest.py
mimetypes.types_map['.R'] = text/x-r-script , mimetypes.guess_type('example.R')[0] = text/x-r2-script
import mimetypes
mimetypes.init()
MIMETYPE_ADDITIONAL_EXTENSIONS = [("text/x-r-script", ".R"), ("text/x-r2-script", ".r"),]
for (mimetype, extension) in MIMETYPE_ADDITIONAL_EXTENSIONS:
    mimetypes.add_type(mimetype, extension, strict=True)
print("mimetypes.types_map['.R'] = %s , mimetypes.guess_type('example.R')[0] = %s" % (mimetypes.types_map['.R'],mimetypes.guess_type('example.R')[0]))

With the current implementation mimetypes.guess_type cannot guess "own" mimetypes which had been added using uppercase letters.

In the docs https://docs.python.org/3/library/mimetypes.html#mimetypes.add_type there is not written, that mimetypes must be written in lowercase letters.

As you can see the implementation of add_type can add "file endings" with capital letters, but they cannot find via mimetypes.guess_type anymore:

cpython/Lib/mimetypes.py

Lines 80 to 95 in 4802344

def add_type(self, type, ext, strict=True):
"""Add a mapping between a type and an extension.
When the extension is already known, the new
type will replace the old one. When the type
is already known the extension will be added
to the list of known extensions.
If strict is true, information will be added to
list of standard types, else to the list of non-standard
types.
"""
self.types_map[strict][ext] = type
exts = self.types_map_inv[strict].setdefault(type, [])
if ext not in exts:
exts.append(ext)

should change to become compatible with the changed implementation of guessing method mimetypes.guess_type.

@ifrh ifrh mentioned this issue May 8, 2022
Closed
@ifrh ifrh changed the title mimetype.guess_type : different return values (PY2.7 to PY3.9.7) vs (PY3.9.11 to PY3.10.4) [proposed lables: stdlib, 3.9, 3.10, 3.11] mimetype.guess_type : different return values (PY2.7 to PY3.9.7) vs (PY3.9.11 to PY3.10.4) May 22, 2022
@ifrh ifrh changed the title [proposed lables: stdlib, 3.9, 3.10, 3.11] mimetype.guess_type : different return values (PY2.7 to PY3.9.7) vs (PY3.9.11 to PY3.10.4) [proposed lables: stdlib, 3.9, 3.10, 3.11] mimetype.guess_type could not find mimetypes added by mimetypes.add_type i.e. in PY3.10.4 // OR : different return values (PY2.7 to PY3.9.7) vs (PY3.9.11 to PY3.10.4) May 23, 2022
@ifrh ifrh changed the title [proposed lables: stdlib, 3.9, 3.10, 3.11] mimetype.guess_type could not find mimetypes added by mimetypes.add_type i.e. in PY3.10.4 // OR : different return values (PY2.7 to PY3.9.7) vs (PY3.9.11 to PY3.10.4) [proposed lables: stdlib, 3.9, 3.10, 3.11] mimetypes.guess_type could not find mimetypes added by mimetypes.add_type i.e. in PY3.10.4 // OR : different return values (PY2.7 to PY3.9.7) vs (PY3.9.11 to PY3.10.4) May 23, 2022
@ifrh ifrh mentioned this issue Jun 3, 2022
Merged
@ifrh ifrh mentioned this issue Jun 18, 2022
Merged
@iritkatriel iritkatriel added the stdlib Python modules in the Lib dir label Apr 7, 2023
@iritkatriel iritkatriel changed the title [proposed lables: stdlib, 3.9, 3.10, 3.11] mimetypes.guess_type could not find mimetypes added by mimetypes.add_type i.e. in PY3.10.4 // OR : different return values (PY2.7 to PY3.9.7) vs (PY3.9.11 to PY3.10.4) mimetypes.guess_type could not find mimetypes added by mimetypes.add_type i.e. in PY3.10.4 // OR : different return values (PY2.7 to PY3.9.7) vs (PY3.9.11 to PY3.10.4) Apr 7, 2023
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CC @kumaraditya303

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