Python concatenates adjacent string or byte literals at compile time. It means that "a" "b" is equivalent to "ab". This
is sometimes used to split a long string on multiple lines. However an implicit string concatenation can also be very confusing. In the following
contexts it might indicate that a comma was forgotten:
- when the two strings are on the same line. This could be interpreted as an incorrectly formatted tuple (parentheses are not mandatory to create
a tuple, only the comma is).
- when the strings are in a list, a set or a tuple.
Code examples
Noncompliant code example
def func():
return "item1" "item2" # Noncompliant: a comma is missing to return a tuple.
["1" # Noncompliant: a comma is missing.
"2",
"a very" # Noncompliant: a "+" is missing.
"long string"]
Compliant solution
def func():
return "item1", "item2"
["1",
"2",
"a very" +
"long string"]
Exceptions
This rule will not raise any issues when there is a visible reason for the string concatenation:
- when the quotes used for both strings are different. This can be used to avoid escaping quotes.
- when the strings or bytes have different prefixes, i.e. "f" for f-strings, "r" for raw, "u" for unicode and no prefix for normal strings.
- when strings are visibly split to avoid long lines of code, i.e. when the first string ends with a space, punctuation or
\n.
