writing for loop variables to a single line of a file in python

Question

Suppose that I have a list X, and its contents to a single line of a file, ie

for var in X:
   if var <some conditions>:
         outfile.write("   "+var)

How can I do this so that each iteration of the loop is not written to a new line in the output file, ie

var1  var2  var3

rather than

var1
var2
var3

in outfile. I know this can be done with a print statement as print x, I can't find the equivalent for write.

Answer 1

Unless your vars already contain trailing linebreaks you won't get multiple lines in your file.

However, you can simply strip off any trailing whitespace using rstrip() :

outfile.write("   " + var.rstrip())

An even better solution would be creating a list with the items and join() ing it. Or simply pass a generator expression to the join() call:

outfile.write('   '.join(var for var in x if condition(var)))

The more explicit version would be this:

results = []
for var in x:
    if condition(var):
        results.append(var)
outfile.write('   '.join(results))

Answer 2

As an alternative to ThiefMaster's excellent answer, the print function in Python3 allows you to specify a file object and an end.

vars = ['one','two','three']

with open("path/to/outfile","w") as outfile:
    for i, entry in enumerate(vars):
        if not condition(var):
            continue
        if i == len(vars):
            _end = ''
        else:
            _end = '    '
        print(entry, end=_end, file=outfile)

However using str.join is probable easier.

vars = ['one','two','three']
with open("path/to/outfile","w") as outfile:
    output_string = '    '.join(map(str.strip, [var for var in vars if condition(var)]))
    print(output_string, end='', file=outfile)
    # or outfile.write(output_string)