Lysandros Nikolaou <[email protected]> added the comment:
It seems that this is actually a bit bigger than this and it is not specific to
f-strings.
The error message *always* changes to `unexpected EOF while parsing` if there
is an error with the last character of the input and no newline follows. For
example, as made clear to me by Guido, there are even differences in error
messages between exec'ing and eval'ing something:
>>> exec('x+')
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
File "<string>", line 1
x+
^
SyntaxError: invalid syntax
>>> eval('x+')
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
File "<string>", line 1
x+
^
SyntaxError: unexpected EOF while parsing
That's because the tokenizer adds an implicit newline to the input string,
before tokenizing it, when the input comes from an exec call. (see
https://github.com/python/cpython/blob/14d5331eb5e6c38be12bad421bd59ad0fac9e448/Parser/tokenizer.c#L648)
And that's not limited to a character missing, as suggested by the error
message. Even when the last character itself generates a SyntaxError, the error
message remains "unexpcted EOF while parsing":
>>> x+@
File "<stdin>", line 1
x+@
^
SyntaxError: invalid syntax
>>> eval('x+@')
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
File "<string>", line 1
x+@
^
SyntaxError: unexpected EOF while parsing
Thus, a very simple fix to the specific fstring problem of this issue would be
to add a newline to the string that gets parsed to the parser in
fstring_compile_expr in ast.c, but I guess it'd be better to fix the tokenizer
itself, if this is considered a bug.
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<https://bugs.python.org/issue40267>
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