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 it looks like a badly formatted tuple. Parenthesises are not mandatory to create a tuple, only the
comma is.
- when the strings are in a list, set or tuple.
Noncompliant Code Example
def func():
return "item1" "item2" # Noncompliant
["1",
"2" # Noncompliant
"3",
"a very very very" # Noncompliant
"very very long string",
"4"]
Compliant Solution
def func():
return "item1", "item2"
["1",
"2",
"3",
"a very very very" +
"very very long string",
"4"]
Exceptions
No issue will be raised 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. (Example: the first string ends with a space, punctuation or
\n).
