Statement Delimiters: Lines and Continuations

A statement in Python normally ends at the end of the line on which it appears. When a statement is too long to fit on a single line, though, a few special rules may be used to make it span multiple lines:

 

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  • Statements may span multiple lines if you’re continuing an open syntactic pair. Python lets you continue typing a statement on the next line if you’re coding something enclosed in a (), {}, or [] pair. For instance, expressions in parentheses and dictionary and list literals can span any number of lines; your statement doesn’t end until the Python interpreter reaches the line on which you type the closing part of the pair (a ), }, or ]). Continuation lines (lines 2 and beyond of the statement) can start at any indentation level you like, but you should try to make them align vertically for readability if possible. This open pairs rule also covers set and dictionary comprehensions in Python 3.0.
  • Statements may span multiple lines if they end in a backslash. This is a somewhat outdated feature, but if a statement needs to span multiple lines, you can also add a backslash (a \ not embedded in a string literal or comment) at the end of the prior line to indicate you’re continuing on the next line. Because you can also continue by adding parentheses around most constructs, backslashes are almost never used. This approach is error-prone: accidentally forgetting a \ usually generates a syntax error and might even cause the next line to be silently mistaken to be a new statement, with unexpected results.
  • Special rules for string literals. As we learned in Chapter 7, triple-quoted string blocks are designed to span multiple lines normally. We also learned in Chapter 7 that adjacent string literals are implicitly concatenated; when used in conjunction with the open pairs rule mentioned earlier, wrapping this construct in parentheses allows it to span multiple lines.
  • Other rules. There are a few other points to mention with regard to statement delimiters. Although uncommon, you can terminate a statement with a semicolon—this convention is sometimes used to squeeze more than one simple (noncompound) statement onto a single line. Also, comments and blank lines can appear anywhere in a file; comments (which begin with a # character) terminate at the end of the line on which they appear.