Question: Short question: What is the most efficient way to check whether a .TXT file contains only characters defined in a selected ISO specification? Question with full context: In the German energy market EDIFACT is used to automatically exchange information. Each file exchanged has a header segment which contains information about the contents of the file. Please find an example of this segment below. UNB+UNOC:3+9903323000007:500+9900080000007:500+250102:0900+Y48A42R58CRR43++++++  As you can see after the UNB+ we find the content UNOC. This tells us which character set is used in the file. In this case it is ISO/IEC 8859-1. I would like a python method which checks whether the EDIFACT file contains only characters specified in ISO/IEC 8859-1. The most simple solution I can think of is doing something like this (pseudo code). ISO_string = "All characters contained in ISO/IEC 8859-1" EDIFACT_string = "Contents of EDIFACT file" is_iso_char = FALSE For EDIFACT_Char in EDIFACT_string: For ISO_char in ISO_string: if EDIFACT_Char = ISO_char: is_iso_char = TRUE break if is_iso_char == FALSE: raiseerror("File contains char not contained in ISO/IEC 8859-1 and needs to be rejected") do_error_handling() is_iso_char = FALSE  I studied business informatics and lack the theoretical background for algorithm theory. This feels like a very inefficient method and since EDIFACT needs to be processed quickly I don't want this functionality to be a bottleneck. Is there an inbuilt pyhton way to do what I want to achieve better? Update #1: I wrote this code as suggested by Barmar. To check it I added the Chinese characters for "World" in the file (世界). I expected .decode to throw an error. However it just decodes the byte string and adds some strange characters at the beginning. File Contents: 世界UNB+UNOC:3+9903323000007:500+9900080000007:500+250102:0900+Y48A42R58CRR43++++++ with open(Filename, "rb") as edifact_file: edifact_bytes = edifact_file.read() try: verified_edifact_string = edifact_bytes.decode(encoding='latin_1', errors='strict') except: print("String does not conform to ISO specification") print(verified_edifact_string)  Prints:  If I just copy Stackoverflow cuts away some of the characters. Edit #2: According to Python documentation the ISO/IEC_8859-1 specification is called latin_1 when using Python's .decode() and .encode() methods.

Answer: Credits to Barmar for suggesting the use of .decode() I found a solution which looks smooth to me. If I encode the string using the latin_1 encoding the Chinese characters seem to not be encoded into bytes. I didn't check but I guess the .encode() method omits them since they don't belong to latin_1. If I then convert the encoded string back using .decode() I get a string without the Chinese characters. If I then compare the original with the encoded and decoded string my question is answered whether characters were contained which don't belong to latin_1. with open(Filename, "r", encoding="utf-8") as edifact_file: edifact_string = edifact_file.read() encoded_edifact_string = edifact_string.encode('latin_1', 'ignore') if encoded_edifact_string.decode('latin_1', 'ignore') == edifact_string: print('Is latin_1') print(edifact_string) print(encoded_edifact_string.decode('latin_1', 'ignore')) else: print('Is no latin_1') print(edifact_string) print(encoded_edifact_string.decode('latin_1', 'ignore'))  Next question is now whether looping over the strings and comparing each character is faster or slower than encoding and decoding and comparing afterwards. But I can check that myself.