How Your Telegram Bot Should Manage User Info
Bots may work in PM, in groups, and in channels — depending on their purpose. These kinds of chats work by different rules, so we will consider them all in the "Chats" chapter.
However, your bot will always interact with users in one way or another. On this page, we’ll discuss some general advice about managing users.
User profile
Users may have no username or no last name — you should keep this in mind while storing their profile info. In groups, this means the bot can't always mention a user by username (see mentions by ID).
In addition, first name, username, and other profile data except for user ID can change over time, so ID is probably the only reliable way to identify a user. User IDs will be explained in more detail later in the book.
A last name isn't always set, so user.full_name is a shortcut for a single string with the first name and the last name when it exists.
user.full_nameUser languages
Bots can access the language setting that a person has configured in their Telegram app. This allows your bot to communicate in users' native languages.
However, the user's language is not always included in all updates. If your bot supports multiple languages, Telegram recommends using the last known language preference when this information is missing from an update.
user.language_code # Sometimes is NoneSeen users
A bot must have seen a user to perform actions related to them (such as mentioning them). The bot sees a user when, for example, it receives a message from the user or retrieves their information by username.
"Seeing" users is not an official term, but rather a conceptual explanation of how Telegram's API works. In technical terms, API requests must include not only the user ID but also a corresponding access hash. The API provides these access hashes along with other user information in updates. Both Bot API and well-designed Telegram API libraries handle access hash caching automatically, so you typically don't need to manage them directly.