[Python] Check if string only contains characters from a certain ISO specification

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.

Continue reading...