Fix: Add thumbnail support for edit_message_media

[skyblade-x]

Description:

By Telegram specification, thumbnails can be used in the following methods:

• InputMediaAnimation
• InputMediaDocument
• InputMediaAudio
• InputMediaVideo

When using send_media_group, everything works correctly. For example:

bot.send_media_group(
    chat_id=CHAT_ID,
    media=[InputMediaAudio(
        media=InputFile(file=audio_path), 
        thumbnail=InputFile(file=thumbnail_path)
    )],
)

Result:

Audio is successfully sent with a thumbnail.

---

However, currently edit_message_media does not support sending thumbnails.

Example with edit_message_media:

initial_message = bot.send_message(CHAT_ID, "Тестовое сообщение.")

  bot.edit_message_media(
     chat_id=CHAT_ID,
     message_id=initial_message.message_id,
     media=InputMediaAudio(
         media=InputFile(file=audio_path),
         thumbnail=InputFile(file=thumbnail_path)
     )
 )

This throws an exception:

The issue is caused because we try to JSON serialize a raw file, but according to Telegram's specification, the thumbnail should be sent using attach://<file_attach_name>, not serialized directly.

Relevant part of the spec:

"The thumbnail should be in JPEG format and less than 200 kB in size. Thumbnails can't be reused and must be uploaded as a new file, so you can pass attach://<file_attach_name> if the thumbnail was uploaded using multipart/form-data."

---

Why this fix is needed:
Without this fix, it is impossible to send or edit media messages with a thumbnail via edit_message_media, even though Telegram's API supports it.

Polite closing:
Please review this PR. Feedback is welcome!

[coder2020official]

Hi, thanks for the PR, I will review it

[Badiboy]

We'll check later after uprade to API 9.0

[Badiboy]

@skyblade-x Any plans to fix or close the PR?

[skyblade-x]

Hi @Badiboy,

Apologies for the delay in responding — I didn’t mean to leave the PR hanging. Thank you for your patience and your feedback.

I’ve now made the requested changes, including aligning the thumbnail check logic with media and handling the optional _thumbnail_name as suggested. I really appreciate the clarity of your review — it helped me understand the style and expectations of the project better.

I'm glad to contribute and happy to make any further improvements if needed. Thanks again for the opportunity to work on this!

[skyblade-x]

@Badiboy, I have fixed your first review, and in my opinion, everything will work as expected.

The condition will only set the media if it has a non-empty string value: media_dict[self._thumbnail_name], only by executing the following code:

[Badiboy]

The condition will only set the media if it has a non-empty string value: media_dict[self._thumbnail_name],

Yep, sorry, I missed this condition.

The issue is that if thumbnail is defined as string - thumbnail will never be processed.

Right?

[skyblade-x]

@Badiboy if thumbnail is defined as string - for example http link to thumbnail it will be processed by this code:

[Badiboy]

ok )