["python","python-3.x","unicode","file-io","decode"]
UnicodeDecodeError: 'charmap' codec can't decode byte X in position Y: character maps to <undefined>

I'm trying to get a Python 3 program to do some manipulations with a text file filled with information. However, when trying to read the file I get the following error: Traceback (most recent call last): File "SCRIPT LOCATION", line NUMBER, in <module> text = file.read() File "C:\Python31\lib\encodings\cp1252.py", line 23, in decode return codecs.charmap_decode(input,self.errors,decoding_table)[0] UnicodeDecodeError: 'charmap' codec can't decode byte 0x90 in position 2907500: character maps to `<undefined>` Editor's note: After reading this Q&A, see How to determine the encoding of text if you need help figuring out the encoding of the file you are trying to open.
The file in question is not using the CP1252 encoding. It's using another encoding. Which one you have to figure out yourself. Common ones are Latin-1 and UTF-8. Since 0x90 doesn't actually mean anything in Latin-1, UTF-8 (where 0x90 is a continuation byte) is more likely. You specify the encoding when you open the file: file = open(filename, encoding="utf-8")