I recently came across the following piece of code. It doesn't look valid because of the single instance of triple quotes but seems to work fine. Can anyone explain what's going on here?
return ("Validation failed(%s): cannot calculate length "
"of %s.""" % (self.name, value))`
All of the strings are concatenated first.
"" is an empty string.
The substitutions are then made.
This is Python's string literal concatenation - essentially, string literals appearing directly next to each other are parsed as a single string:
>>> 'foo' 'bar'
'foobar'
In your example, you have three string literals in a row (the last is "", the empty string) being concatenated this way, rather than a single multi-line literal that is terminated but not started with triple quotes.
When you use String on multiple line you can add " to make a single line output as string are concatenate first. You can read the line as :
return ("Validation failed(%s): cannot calculate length " //1st line
"of %s." //2nd line
"" % (self.name, value)) //3rd line (empty)
If you can modify the code, note that the % syntax for formatting strings is becoming outdated. You should use str.format() if your version of Python supports it:
return "Validation failed({0}): cannot calculate length of {1}.".format(self.name, value)
If it needs to span multiple lines, use:
return ("Validation failed({0}): " +
"cannot calculate length of {1}.".format(self.name, value))
+, because of exactly the same string literal concatenation in the original code.