Python join why is it string join list instead of list join string

0 votes

This has always confused me. It seems like this would be nicer:

my_list = ["Hello", "world"]

print my_list.join("-")

# Produce: "Hello-world"

Than this:

my_list = ["Hello", "world"]

print "-".join(my_list)

# Produce: "Hello-world"

Is there a specific reason it is like this?

Jul 30, 2018 in Python by bug_seeker
• 15,510 points
828 views

1 answer to this question.

0 votes

This is because join is a "string" method! It creates a string from any iterable. If we stuck the method on lists, what about when we have iterables that aren't lists?

What if you have a tuple of strings? If this were a list method, you would have to cast every such iterator of strings as a list before you could join the elements into a single string! For example:

some_strings = ('foo', 'bar', 'baz')

Let's roll our own list join method:

class OurList(list): def join(self, s): return s.join(self)

And to use it, note that we have to first create a list from each iterable to join the strings in that iterable, wasting both memory and processing power:

>>> l = OurList(some_strings)

# step 1, create our list

>>> l.join(', ')

# step 2, use our list join method! 'foo, bar, baz'

So we see we have to add an extra step to use our list method, instead of just using the builtin string method:

>>> ' | '.join(some_strings)

# a single step!

'foo | bar | baz'

answered Jul 30, 2018 by Priyaj
• 58,020 points

Related Questions In Python

0 votes
1 answer

Python join: why is it string.join(list) instead of list.join(string)?

950down voteaccepted It's because any iterable can be ...READ MORE

answered May 15, 2018 in Python by aryya
• 7,460 points
923 views
0 votes
0 answers

Is it possible to get a list of keywords in Python?

I want to obtain a string list ...READ MORE

Nov 24, 2022 in Python by sarit
• 1,830 points
471 views
0 votes
1 answer

Why is Python scoping made the way it is?

The likeliest answer is that it just ...READ MORE

answered Nov 5, 2018 in Python by Nymeria
• 3,560 points

edited Dec 17, 2018 by Nymeria 697 views
0 votes
1 answer

What is the recommended way to randomize a list of strings using Python?

Hi. Nice question. Here is the simplified answer ...READ MORE

answered Jan 18, 2019 in Python by Nymeria
• 3,560 points
953 views
0 votes
2 answers
+1 vote
2 answers

how can i count the items in a list?

Syntax :            list. count(value) Code: colors = ['red', 'green', ...READ MORE

answered Jul 7, 2019 in Python by Neha
• 330 points

edited Jul 8, 2019 by Kalgi 4,450 views
0 votes
1 answer
0 votes
1 answer

Why is it string.join(list) instead of list.join(string)?

It's because any iterable can be joined ...READ MORE

answered Dec 2, 2020 in Python by Gitika
• 65,770 points
818 views
0 votes
1 answer

Convert string list of dict from csv into JSON object in python

You can use the ast module Ex: import ast s = """[{'10': ...READ MORE

answered Sep 12, 2018 in Python by Priyaj
• 58,020 points
2,570 views
0 votes
1 answer

Convert string list of dict from csv into JSON object in python

You can use the ast module Ex: import ast s = """[{'10': ...READ MORE

answered Sep 24, 2018 in Python by Priyaj
• 58,020 points
1,038 views
webinar REGISTER FOR FREE WEBINAR X
REGISTER NOW
webinar_success Thank you for registering Join Edureka Meetup community for 100+ Free Webinars each month JOIN MEETUP GROUP