Fix Python – What is the most efficient string concatenation method in Python?


Asked By – mshsayem

Is there an efficient mass string concatenation method in Python (like StringBuilder in C# or StringBuffer in Java)?

I found following methods here:

  • Simple concatenation using +
  • Using a string list and the join method
  • Using UserString from the MutableString module
  • Using a character array and the array module
  • Using cStringIO from the StringIO module

What should be used and why?

(A related question is here.)

Now we will see solution for issue: What is the most efficient string concatenation method in Python?


If you know all components beforehand once, use the literal string interpolation, also known as f-strings or formatted strings, introduced in Python 3.6.

Given the test case from mkoistinen’s answer, having strings

domain = ''
lang = 'en'
path = 'some/really/long/path/'

The contenders and their execution time on my computer using Python 3.6 on Linux as timed by IPython and the timeit module are

  • f'http://{domain}/{lang}/{path}'0.151 µs

  • 'http://%s/%s/%s' % (domain, lang, path) – 0.321 µs

  • 'http://' + domain + '/' + lang + '/' + path – 0.356 µs

  • ''.join(('http://', domain, '/', lang, '/', path))0.249 µs (notice that building a constant-length tuple is slightly faster than building a constant-length list).

Thus the shortest and the most beautiful code possible is also fastest.

The speed can be contrasted with the fastest method for Python 2, which is + concatenation on my computer; and that takes 0.203 µs with 8-bit strings, and 0.259 µs if the strings are all Unicode.

(In alpha versions of Python 3.6 the implementation of f'' strings was the slowest possible – actually the generated byte code is pretty much equivalent to the ''.join() case with unnecessary calls to str.__format__ which without arguments would just return self unchanged. These inefficiencies were addressed before 3.6 final.)

This question is answered By – Antti Haapala — Слава Україні

This answer is collected from stackoverflow and reviewed by FixPython community admins, is licensed under cc by-sa 2.5 , cc by-sa 3.0 and cc by-sa 4.0