On 8/9/2019 9:08 AM, Nick Coghlan wrote:
On Sat, 10 Aug 2019 at 01:44, Guido van Rossum <gu...@python.org> wrote:
This discussion looks like there's no end in sight. Maybe the Steering Council
should take a vote?
I find the "Our deprecation warnings were even less visible than
normal" argument for extending the deprecation period compelling.
I also think the UX of the warning itself could be reviewed to provide
a more explicit nudge towards using raw strings when folks want to
allow arbitrary embedded backslashes. Consider:
SyntaxWarning: invalid escape sequence \,
vs something like:
SyntaxWarning: invalid escape sequence \, (Note: adding the raw
string literal prefix, r, will accept all non-trailing backslashes)
After all, the habit we're trying to encourage is "If I want to
include backslashes without escaping them all, I should use a raw
string", not "I should memorize the entire set of valid escape
sequences" or even "I should always escape backslashes".
Cheers,
Nick.
The reason I never use raw strings is in the documentation, it is
because \ still has a special meaning, and the first several times I
felt the need for raw strings, it was for directory names that wanted to
end with \ and couldn't. Quoted below. Also relevant to the discussion
is the "benefit" of leaving the backslash in the result of an illegal
escape, which no one has mentioned in this huge thread.
Unlike Standard C, all unrecognized escape sequences are left in the
string unchanged, i.e., /the backslash is left in the result/. (This
behavior is useful when debugging: if an escape sequence is mistyped,
the resulting output is more easily recognized as broken.) It is also
important to note that the escape sequences only recognized in string
literals fall into the category of unrecognized escapes for bytes
literals.
Changed in version 3.6: Unrecognized escape sequences produce a
DeprecationWarning. In some future version of Python they will be
a SyntaxError.
Even in a raw literal, quotes can be escaped with a backslash, but the
backslash remains in the result; for example, |r"\""| is a valid
string literal consisting of two characters: a backslash and a double
quote; |r"\"| is not a valid string literal (even a raw string cannot
end in an odd number of backslashes). Specifically, /a raw literal
cannot end in a single backslash/ (since the backslash would escape
the following quote character). Note also that a single backslash
followed by a newline is interpreted as those two characters as part
of the literal, /not/ as a line continuation.
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