Python - read - rewrite on a text file (Driving me crazy)

# read all three files in as strings
file1_str = '''\
ab

cd

ef
'''

file2_str = '''\
g

h

i
'''

file3_str = '''\
j

k

l
'''

# split each string at whitespace to a list
list1 = file1_str.split()
#print(list1)  # test
list2 = file2_str.split()
list3 = file3_str.split()

# combine the lists with zip()
#print(zip(list1, list2, list3))  # test

mystr = ""
for c1, c2, c3 in zip(list1, list2, list3):
    mystr += c1 + c2 + c3 + '\n' + '\n'

print(mystr)

# now save mystr to a text file

''' my result >>>
abgj

cdhk

efil

'''

# this program works for sufficiently nice input files.
# The input files need to be rectangular in terms of fields,
# and they need to have the same number of rows.

print('warning!  This program creates files on your system.')
print('remove these lines if OK.')
1/0

def transpose(inp,out=None):
    with open(inp) as inf:
        rows = [row.strip() for row in inf.readlines()]
    if out is None:
        out = inp + '.T'
    with open(out,'w') as ouf:
        for fields in zip(*(row.split() for row in rows)): # "1 liner" is nasty
            ouf.write(' '.join(fields)+'\n')

def laminate(out,*inp):
    '''
        >>> laminate('joinedFile','source.1','source.2','source.n')
        >>>
    '''
    for f in inp:
        transpose(f)
    with open(out+'.T','w') as ouf:
        for f in inp:
            with open(f+'.T') as inf:
                ouf.write(inf.read())
    transpose(out+'.T',out)

if '__main__' == __name__:
    import sys
    if len(sys.argv) < 3:
        print('use: %s input1 [input2 ...] output')
        sys.exit(1)
    laminate(sys.argv[-1],*(sys.argv[1:-1]))