[FIXED] Has the Python Language Reference made an error of omission when it comes to string literals?

Issue

I've been studying the Python Language Reference carefully, for some Anki flashcards I'm writing. And it appears I've hit a snag while going over string literals.

See here: The function call print("can't") returns can't.

But I've been unable to find anything in the docs that suggests this is even possible!

Consider this excerpt of the formal definition:

shortstring     ::= "'" shortstringitem* "'" | '"' shortstringitem* '"'
longstring      ::= "'''" longstringitem* "'''" | '"""' longstringitem* '"""'
shortstringitem ::= shortstringchar | stringescapeseq
longstringitem  ::= longstringchar | stringescapeseq
shortstringchar ::= <any source character except "\" or newline or the quote>
longstringchar  ::= <any source character except "\">
stringescapeseq ::= "\" <any source character>`

Source

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As you may be able to tell, the sequence "can't" is a short-string. That's because it is a group of zero or more short-string items surrounded by matching groups of double quotes.

And short-string items may either be short-string characters or string escape sequences.

Since there are no string escape sequences in the sequence "can't", let's look at short-string characters. The definition says that the quote (') is not a short-string character.

Since the quote is not a short-string character, it makes sense that print('can't') throws a syntax error. Why doesn't print("can't") follow the same rules?

I feel like the Python Language Reference has made an error of omission here. Thoughts?

Solution

Since "can't" starts with a double quote, you're allowed to have a single quote in the literal.

shortstringchar ::= <any source character except "\" or newline or the quote>

By "the quote" the specification means the character (either ' or ") that opened the string literal. This allows you to have either single or double quotes in a string literal (without escaping) by enclosing the literal in the opposite quote characters.

Answered By - Bill the Lizard