read from file with mixed encodings in Python3

[Jaroslav Dobrek]

Hello,

in Python3, I often have this problem: I want to do something with
every line of a file. Like Python3, I presuppose that every line is
encoded in utf-8. If this isn't the case, I would like Python3 to do
something specific (like skipping the line, writing the line to
standard error, ...)

Like so:

try:
   ....
except UnicodeDecodeError:
  ...

Yet, there is no place for this construction. If I simply do:

for line in f:
    print(line)

this will result in a UnicodeDecodeError if some line is not utf-8,
but I can't tell Python3 to stop:

This will not work:

for line in f:
    try:
        print(line)
    except UnicodeDecodeError:
        ...

because the UnicodeDecodeError is caused in the "for line in f"-part.

How can I catch such exceptions?

Note that recoding the file before opening it is not an option,
because often files contain many different strings in many different
encodings.

Jaroslav