[PyQt] Implicit latin1 encoding for QByteArray

[Florian Bruhin]

Hi,

The PyQt documentation says:

    If Qt expects a QByteArray then PyQt5 will also accept a str that
    contains only Latin-1 characters, or a bytes.

I don't know the background/rationale for this, but (at least with
Python3, probably things are different on py2) I'd have expected a
TypeError for anything else than a bytes object.

I got bitten by this in a rather obscure place, in the error page for
a QWebPage (code just for illustration, not tested):

# ----

class WebPage(QWebPage):

    def extension(self, ext, opt, out):
        if ext != QWebPage.ErrorPageExtension:
            return False
        errpage = sip.cast(out, QWebPage.ErrorPageExtensionReturn)
        info = sip.cast(opt, QWebPage.ErrorPageExtensionOption)
        url = info.url.toDisplayString()
        errpage.content = some_code_that_renders_errpage(url)
        return True

# ----

I got a confusing exception when there was an error page on an URL
with UTF-8 chars with it:

    UnicodeEncodeError: 'latin-1' codec can't encode character
    '\u2713' in position 213: ordinal not in range(256)

(with the traceback pointing on the erropage.content line).

If QByteArray would've done what Python3 does (bytes/string are
incompatible), I'd have noticed my mistake right away, this way it
exploded unexpectedly ;)

Of course this might be a breaking change, but I thought I'd propose
it anyways ;)

Maybe another option would be to implicitely encode to UTF-8 for
ErrorPageExtensionReturn::content if that's possible? After all,
ErrorPageExtensionReturn::encoding defaults to 'utf-8', so Qt is
expecting UTF-8 data there. (Now that I think of it that'd also mean
it'd silently break with data that is valid Latin1 but invalid UTF8).

Florian

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