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How to concatenate items in a list to a single string?


Question

Is there a simpler way to concatenate string items in a list into a single string? Can I use the str.join() function?

E.g. this is the input ['this','is','a','sentence'] and this is the desired output this-is-a-sentence

sentence = ['this','is','a','sentence']
sent_str = ""
for i in sentence:
    sent_str += str(i) + "-"
sent_str = sent_str[:-1]
print sent_str
2020/08/05
1
608
8/5/2020 12:32:10 AM

Accepted Answer

Use join:

>>> sentence = ['this','is','a','sentence']
>>> '-'.join(sentence)
'this-is-a-sentence'
2012/09/17
1123
9/17/2012 5:48:06 AM

A more generic way to convert python lists to strings would be:

>>> my_lst = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
>>> my_lst_str = ''.join(map(str, my_lst))
>>> print(my_lst_str)
'12345678910'
2016/04/19

It's very useful for beginners to know why join is a string method.

It's very strange at the beginning, but very useful after this.

The result of join is always a string, but the object to be joined can be of many types (generators, list, tuples, etc).

.join is faster because it allocates memory only once. Better than classical concatenation (see, extended explanation).

Once you learn it, it's very comfortable and you can do tricks like this to add parentheses.

>>> ",".join("12345").join(("(",")"))
Out:
'(1,2,3,4,5)'

>>> list = ["(",")"]
>>> ",".join("12345").join(list)
Out:
'(1,2,3,4,5)'
2020/02/05

Although @Burhan Khalid's answer is good, I think it's more understandable like this:

from str import join

sentence = ['this','is','a','sentence']

join(sentence, "-") 

The second argument to join() is optional and defaults to " ".

EDIT: This function was removed in Python 3

2018/01/20

We can also use Python's reduce function:

from functools import reduce

sentence = ['this','is','a','sentence']
out_str = str(reduce(lambda x,y: x+"-"+y, sentence))
print(out_str)
2020/02/23

We can specify how we have to join the string. Instead of '-', we can use ' '

sentence = ['this','is','a','sentence']
s=(" ".join(sentence))
print(s)
2019/10/18