When I first started messing around with python strings and unicode, It took me awhile to understand the jargon of decode and encode too, so here's my post from here that may help:

Think of decoding as what you do to go from a regular bytestring to unicode and encoding as what you do to get back from unicode. In other words:

You de-code a str to produce a unicode string (in Python 2)

and en-code a unicode string to produce a str (in Python 2)

So:

unicode_char = u'\xb0'

encodedchar = unicode_char.encode('utf-8')

encodedchar will contain your unicode character, displayed in the selected encoding (in this case, utf-8).

The same principle applies to Python 3. You de-code a bytes object to produce a str object. And you en-code a str object to produce a bytes object.

I have a set of UTF-8 texts I have scraped from web pages

If they can't be read with the script you've shown, then these are not actually UTF-8 encoded files.

We have to know about the code which wrote the files in the first place to tell the correct way to decode. However, the ’ character is 0x92 byte in code page 1252, so try using that encoding instead, i.e.:

with open("files/" + filename.name, encoding="cp1252") as infile:
    text = infile.read()

Ignoring decoding errors corrupts the data, so it's best to use the correct decoder when possible, so try and do that first! However, about this part of the question:

Regardless, is there some way to make the codec tolerate such encoding errors? For example, Perl simply substitutes a question mark for any character it can't decode. Is there some way to get Python to do the same?

Yes, you can specify errors="replace"

>>> with open("/tmp/f.txt", "w", encoding="cp1252") as f:
...     f.write('this is a right quote: \N{RIGHT SINGLE QUOTATION MARK}')
... 

>>> with open("/tmp/f.txt", encoding="cp1252") as f:
...     print(f.read())  # using correct encoding
... 
this is a right quote: ’

>>> with open("/tmp/f.txt", encoding="utf-8", errors="replace") as f:
...     print(f.read())  # using incorrect encoding and replacing errors
this is a right quote: �

Your file doesn't appear to use the UTF-8 encoding. It is important to use the correct codec when opening a file.

You can tell open() how to treat decoding errors, with the errors keyword:

errors is an optional string that specifies how encoding and decoding errors are to be handled–this cannot be used in binary mode. A variety of standard error handlers are available, though any error handling name that has been registered with codecs.register_error() is also valid. The standard names are:

• 'strict' to raise a ValueError exception if there is an encoding error. The default value of None has the same effect.
• 'ignore' ignores errors. Note that ignoring encoding errors can lead to data loss.
• 'replace' causes a replacement marker (such as '?') to be inserted where there is malformed data.
• 'surrogateescape' will represent any incorrect bytes as code points in the Unicode Private Use Area ranging from U+DC80 to U+DCFF. These private code points will then be turned back into the same bytes when the surrogateescape error handler is used when writing data. This is useful for processing files in an unknown encoding.
• 'xmlcharrefreplace' is only supported when writing to a file. Characters not supported by the encoding are replaced with the appropriate XML character reference &#nnn;.
• 'backslashreplace' (also only supported when writing) replaces unsupported characters with Python’s backslashed escape sequences.

Opening the file with anything other than 'strict' ('ignore', 'replace', etc.) will then let you read the file without exceptions being raised.

Note that decoding takes place per buffered block of data, not per textual line. If you must detect errors on a line-by-line basis, use the surrogateescape handler and test each line read for codepoints in the surrogate range:

import re

_surrogates = re.compile(r"[\uDC80-\uDCFF]")

def detect_decoding_errors_line(l, _s=_surrogates.finditer):
    """Return decoding errors in a line of text

    Works with text lines decoded with the surrogateescape
    error handler.

    Returns a list of (pos, byte) tuples

    """
    # DC80 - DCFF encode bad bytes 80-FF
    return [(m.start(), bytes([ord(m.group()) - 0xDC00]))
            for m in _s(l)]

E.g.

with open("test.csv", encoding="utf8", errors="surrogateescape") as f:
    for i, line in enumerate(f, 1):
        errors = detect_decoding_errors_line(line)
        if errors:
            print(f"Found errors on line {i}:")
            for (col, b) in errors:
                print(f" {col + 1:2d}: {b[0]:02x}")

Take into account that not all decoding errors can be recovered from gracefully. While UTF-8 is designed to be robust in the face of small errors, other multi-byte encodings such as UTF-16 and UTF-32 can't cope with dropped or extra bytes, which will then affect how accurately line separators can be located. The above approach can then result in the remainder of the file being treated as one long line. If the file is big enough, that can then in turn lead to a MemoryError exception if the 'line' is large enough.