String syntax allows two strings in a row with no operator?

Question

I just discovered what I thought was a typo but Python accepts it.

foo = {'a': 'b'}
foo.get('a'"")

returns 'b'. Where in Python is 'a'"" defined as a valid parameter to a function?

Answer 1

Python concatenates all consecutive strings. It doesn't matter if that's in a function or elsewhere.

See the String literal concatenation section of the reference documentation:

Multiple adjacent string literals (delimited by whitespace), possibly using different quoting conventions, are allowed, and their meaning is the same as their concatenation.

This is done at the parsel level; the final bytecode stores just the one string object. See What is under the hood of x = 'y' 'z' in Python?

The feature was copied from C. From a (failed) proposal to remove the feature:

Many Python parsing rules are intentionally compatible with C. [...] In C, implicit concatenation is the only way to join strings without using a (run-time) function call to store into a variable.

The feature is very useful when producing long strings:

long_value = (
    'The quick brown fox jumped over the lazy fox and kept '
    'the string within the 80 character boundary.'
)