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I want to join the elements of two lists into one list and add some characters, like so:

list_1 = ['some1','some2','some3']
list_2 = ['thing1','thing2','thing3']

joined_list = ['some1_thing1', 'some2_thing2', 'some3_thing3']

however i don't know in advance how many lists I will have to do this for, i.e. I want to do this for an arbitrary number of lists

Also, I currently receive a list in the following form:

list_A = [('some1','thing1'),('some2','thing2'),('some3','thing3')]

so I split it up into lists like so:

list_B = [i for i in zip(*list_A)]

I do this because sometimes I have an int instead of a string 

list_A = [('some1','thing1',32),('some1','thing1',42),('some2','thing3', 52)]

so I can do this after 

list_C = [list(map(str,list_B[i])) for i in range(0,len(list_B)]

and basically list_1 and list_2 are the elements of list_C.

So is there a more efficient way to do all this ?

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3 Answers 3

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3

Try this if you are using python>=3.6:

[f'{i}_{j}' for i,j in zip(list_1, list_2)]

If you using python3.5, you can do this:

 ['{}_{}'.format(i,j) for i,j in zip(list_1, list_2)]

also you can use this if you don't want to use formatted string:

['_'.join([i,j]) for i,j in zip(list_1, list_2)]
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4 Comments

Is there a way to make this apply for an arbitrary number of lists ?
@AnarKi yes, the below answer, but it was suppose to be over the zip object, not list_A.
@juanpa.arrivillaga below might change with votes or whatnot.
@AnarKi what do you mean by arbitrary number of lists? you give an example?
2

You can join function like this on the base list_A, itself, no need to split it for probable int values:

list_A = [('some1','thing1',32),('some1','thing1',42), ('some2','thing3', 52)] 
["_".join(map(str, i)) for i in list_A]

Output:

['some1_thing1_32', 'some1_thing1_42', 'some2_thing3_52']

Update:

For you requirement, where you want to ignore last element for last tuple in your list_A, need to add if-else condition inside the list-comprehension as below:

["_".join(map(str, i)) if list_A.index(i) != len(list_A)-1 else "_".join(map(str, i[:-1])) for i in list_A  ]

Updated Output:

['some1_thing1_32', 'some1_thing1_42', 'some2_thing3']
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10 Comments

i already tried this. This will join the elements themselves which is not what I want, i.e. some1_some2_some3 etc.
@AnarKi, I added the output, is this not same as what you mentioned in joined_list?
This works fine, I actually tried on list_B that's why it didn't work... sorry about that
One more thing, do you know if the last element of list_A can be omitted sometimes ? like list_A[:-1],m resulting in this: ['some1_thing1', 'some1_thing1, 'some2_thing3'] without 32,42..
Thanks, in that case, would you like to upvote and accept?
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1

For ignoring the last element of every tuple in list_A, I found this to be the quickest way:

["_".join(map(str, i)) for i in [x[:-1] for x in list_A] ]
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2 Comments

this will ignore third element for all cases. is that expected?
yes that is what I wanted, basically exclude the last element of each tuple

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