Question

I m trying to read a list of items from a text file and format with square brackets and separators like this: [ item1 , item2 , .... last_item ] but I m having trouble with the beginning and end item for which I always get: ..., last_item , ], so I do not want the last , to be there.

In python I ve write:

out_list = "[ "
for line in open(file_in):  
    out_list += line                #append the item to the list
    out_accession_list += " , "     #add the separator
out_accession_list += "]"           #add the final closed bracket
return out_list

I realize that this is a basic loop question, but I can t think of the best way to do it. Should I use a try final statement, should it be a while loop, or should I count the number of lines first and then use a loop with a range?

Help much appreciated.

Thanks, John

Answer 1

Read in all your lines and use the string.join() method to join them together.

lines = open(file_in).readlines()

out_list = "[ " + " , ".join(lines) + " ]"

Additionally, join() can take any sequence, so reading the lines isn t necessary. The above code can be simplified as:

out_list = "[ " + " , ".join(open(file_in)) + " ]"

Answer 2

out_list = []
for line in open(file_in):
    out_list.append(" " + line + " ")
return "[" + ",".join(out_list) + "]"

Answer 3

You "right strip" for "," the result before adding the last "]".

e.g. use the string.rstrip(",")

Answer 4

Or

result = "[ "
for line in open(file_in):
    if len(result) > 0:
        result += " , " 
    result += line
result += " ]"
return result

Answer 5

def do(filepath):
    out = []
    for line in open(filepath,  r ):
        out.append(" " + line.strip() + " ")
    return out.__str__()

Answer 6

Your desired output format is exactly Python s standard printable representation of a list. So an easy solution is to read the file, create a list with each line as a string element (stripping the end-of-line of each), and call the Python built-in function repr to produce a string representation of the list:

>>> repr([line.rstrip() for line in open(file_in)])
"[ item1 ,  item2 ,  item3 ]"

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