EDIT: chardet seems to be unmantained but most of the answer applies. Check https://pypi.org/project/charset-normalizer/ for an alternative
Correctly detecting the encoding all times is impossible.
(From chardet FAQ:)
However, some encodings are optimized
for specific languages, and languages
are not random. Some character
sequences pop up all the time, while
other sequences make no sense. A
person fluent in English who opens a
newspaper and finds “txzqJv 2!dasd0a
QqdKjvz” will instantly recognize that
that isn’t English (even though it is
composed entirely of English letters).
By studying lots of “typical” text, a
computer algorithm can simulate this
kind of fluency and make an educated
guess about a text’s language.
There is the chardet library that uses that study to try to detect encoding. chardet is a port of the auto-detection code in Mozilla.
You can also use UnicodeDammit. It will try the following methods:
- An encoding discovered in the document itself: for instance, in an XML declaration or (for HTML documents) an http-equiv META tag. If Beautiful Soup finds this kind of encoding within the document, it parses the document again from the beginning and gives the new encoding a try. The only exception is if you explicitly specified an encoding, and that encoding actually worked: then it will ignore any encoding it finds in the document.
- An encoding sniffed by looking at the first few bytes of the file. If an encoding is detected at this stage, it will be one of the UTF-* encodings, EBCDIC, or ASCII.
- An encoding sniffed by the chardet library, if you have it installed.