What\'s the Most Efficient Way to Concatenate Strings in Python 3?

Which is the Preferred Way to Concatenate a String in Python?

In Python, strings are immutable. To append a string to an existing variable, one must either use the or = operator or create a list, append strings to it, and join the list to form a new string using join().

The Traditional Approach: = or

The traditional and most commonly used method is to append strings directly using or =. Both versions perform similarly in terms of speed.

s += stringfromelsewhere

This method is straightforward and easy to read, making it a popular choice for simple concatenation tasks.

The List-Join Method: append() and join()

Some developers advocate for using a list to store individual strings and then joining them using join(). They argue that appending to a list is faster than appending to a string.

s = []
s.append(somestring)
# later
s = ''.join(s)

Performance Analysis

In Python 3, appending to a string ( and =) consistently outperforms appending to a list (append() and join()) for both short and long strings. Even in cases where the resulting string is over 100MB in size, and = remain faster.

Historical Context

The recommendation to use append() and join() may have originated in Python 2, where concatenating long strings could be relatively slow. However, this performance issue was resolved in later versions of Python, making the and = operators the preferred method for string concatenation in Python 3.

Use Case Considerations

While and = are generally faster, the append() and join() method can be advantageous for clarity or readability, especially when concatenating strings with separators like spaces or newlines.

Conclusion

In Python 3, the recommended way to concatenate strings is to use or =. These operators are efficient and easy to use. The append() and join() method is not obsolete but may be advantageous in certain use cases for improved readability.

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