python tip

Concatenate Strings with .join()

Let's say we have a list with different strings, and we want to combine all elements to one string, separated by a space between each word. The bad way is to do it like this:

list_of_strings = ["Hello", "my", "friend"]

# BAD:
my_string = ""
for i in list_of_strings:
    my_string += i + " " 

We defined an empty string, then iterated over the list, and then appended the word and a space to the string. As you should know, a string is an immutable element, so here we have to create new strings each time. This code can be very slow for large lists, so you should immediately forget this approach! Much better, much faster, and also much more concise is to the .join() method:

list_of_strings = ["Hello", "my", "friend"]
my_string = " ".join(list_of_strings)

This combines all the elements into one string and uses the string in the beginning as a separator. So here we use a string with only a space. If we were for example to use a comma here, then the final string has a comma between each word. This syntax is the recommended way to combine a list of strings into one string.