Python file comparison program

Question

Personal I am with a doubt and a great difficulty to create a program that reads 2 files, example doc1.txt and doc2.txt, within the files has the following data:

doc1.txt   doc2.txt
1            1
1            2
2            5
3            6
4            7
5            7
10           8
             9

It should be line by line and compare, for example if doc1 data 1 is == to doc2 data 1, doc1 > doc2 or <, record the data in a doc called result.txt in sequence with each given line by line. He must record the data in sequence.

Just follow my code:

#Arquivos de Texto
with open('doc1.txt', 'r', encoding='UTF-8') as doc1:
    arq1: int= doc1.readline()

with open('doc2.txt', 'r', encoding='UTF-8') as doc2:
    arq2: int = doc2.readline()

if arq1 == arq2:
    with open('resultado.txt', 'w') as res:
         r: int = res.write(arq1)

elif arq1 > arq2:
    with open('resultado.txt', 'w') as res:
         r: int = res.write(arq1)

elif arq1 < arq2:
    with open('resultado.txt', 'w') as res:
         r: int = res.write(arq2)
else:
    print('Error')

It only compares the first data 1 == 1 and writes to the file resultado.txt and then he doesn’t read any more data from the files.

I don’t know what I’m doing wrong.

Answer 1

As commented, the problem of reading only the first line is that you used the method readline, that reads only one line. To read them all, you will need to iterate over the file with a repeat loop.

As explained in What’s with no Python for?, you can use multiple contexts managers in the same with, which would simplify your program:

with open('entrada_1.txt') as arquivo_1, \
     open('entrada_2.txt') as arquivo_2, \
     open('saida.txt', 'w') as saida:
    numeros_arquivo_1 = (int(numero.strip()) for numero in arquivo_1)
    numeros_arquivo_2 = (int(numero.strip()) for numero in arquivo_2)
    for a, b in zip(numeros_arquivo_1, numeros_arquivo_2):
        saida.write(f'{a}\n' if a >= b else f'{b}\n')

Since you are reading a file, it is natural that the data come as string, then it is necessary to convert them to numerics. Objects numeros_arquivo_1 and numeros_arquivo_2 are exactly that - the strip is to remove line break.

With the zip, we group the values of the two files to facilitate the comparison between a and b. If the value in file 1 is greater than or equal to that of file 2, the value of a, otherwise, the value of b. It is important to point out that the zip uses the smallest file as a reference, ignoring the extra values of the largest. If you need to compare based on the largest file, use the function itertools.zip_longest.