The Python Apprentice

Joining strings

For joining large numbers of strings, avoid using the + or += operators. Instead, the  join() method should be preferred because it is substantially more efficient. This is because concatenation using the addition operator or it's augmented assignment version can lead to the generation of large numbers of temporaries, with consequent costs for memory allocation and copies. Let's see how join() is used.

The join() is a method on str which takes a collection of strings as an argument and produces a new string by inserting a separator between each of them. An interesting aspect of join() is how the separator is specified: it is the string on which join() is called.

As with many parts of Python, an example is the best explanation. ...