The number of occurrences of statistical characters

[buran]

There are special characters that need to be escaped if you want to use them literally. The error comes at the \ which is RegEx own escape char. So the result is (when not escaped) is invalid pattern.

import re, sre_constants
 
patter = [chr(i) for i in range(33,126)]
 
with open("a.txt","r") as file:
    content = file.read()
    for i in patter:
        try:
            result = len(re.findall(r"[%s]" % i,content))
        except sre_constants.error:
            print('error with {}'.format(i))

Output:
error with \
error with ^

change the for body like this

        try:
            result = len(re.findall(r"[%s]" % i,content))
        except sre_constants.error:
            result = len(re.findall(r"[\%s]" % i,content))
        if result != 0:
            print("%s:%d" % (i, result))  

and it work.

That said, note that you also need to escape chars like *, ? or . in order to search for them literally. I will leave this to you