Program that reads 4 files and outputs contents of it into another file after formatting it

The below Python 3 program scans 4 files a.txt, b.txt, c.txt, d.txt and then outputs the read data into a file output.txt in a formatted way. The first line of each file is guaranteed to have a header and the second line of each file will be blank. I'm required to scan those four files.

Program:

def main():
    with open('a.txt', 'r') as file_a, open('b.txt', 'r') as file_b, open('c.txt', 'r') as file_c, open('d.txt', 'r') as file_d:
        lines1, lines2, lines3, lines4 = file_a.readlines(), file_b.readlines(), file_c.readlines(), file_d.readlines()
        lines = [lines1, lines2, lines3, lines4]
        number_of_spaces = 5

        assert len(lines1) == len(lines2) == len(lines3) == len(lines4), "Error. Different number of lines found in the files"

        row, column = 0, 1
        with open('output.txt', 'w') as output:

            while row < len(lines):
                output.write(lines[row][0].strip() + ' ' * number_of_spaces)
                row += 1
            output.write('\n')
            row = 0

            while column < len(lines1):
                while row < len(lines):
                    output.write(lines[row][column].strip() + ' ' * (number_of_spaces + len(lines[row][0].strip()) - len(lines[row][column].strip())))
                    row += 1
                output.write('\n')    
                column += 1
                row = 0        

if __name__ == "__main__":
    main()

When executed gives output.txt:

Sl.No     Elements     Abbreviation     Mass     

1         Hydrogen     H                1        
2         Helium       He               4        
3         Lithium      Li               7        
4         Beryllium    Be               9        
...
98        Californium  Cf               251      
99        Einsteinium  Es               252      
100       Fermium      Fm               257

Is there any room for improvement?

Additional information (if necessary):

Note that ... in the files me

I think that zip can save you some work:

with open('a.txt', 'r') as file_a, open('b.txt', 'r') as file_b, \
     open('c.txt', 'r') as file_c, open('d.txt', 'r') as file_d:
         for content in zip(file_a.readlines(), file_b.readlines(),
                            file_c.readlines(), file_d.readlines()):
             print(content)

The above is just a basic example, you will want to:

• Add error checking (asserting for example)

• Add an output file

• Add necessary spaces

StackExchange Code Review Q#94648, answer score: 2