Question

It does work but it doesn’t replace the letters.
First I open one file, and write the content to another. And then to the second file I replace some specific letters, but it doesn’t work, An
any idea?
The code:

def  copy_file():

    f=open("cartas.txt","r")
    g=open("copiar.txt","r+")
    g.writelines(f)
    f.close()

    for line in g:
       line = line.replace("s","ch")
       g.write(line) 
    g.close()

copy_file()

Answer 1

You are trying to iterate over the lines in g and also write the modified lines to g. And before that you actually copy the contents from f into g.

What you should be doing is iterating over the lines of f and write them to g while converting them directly:

f = open('cartas.txt', 'r')
g = open('copiar.txt', 'r+')

for line in f:
    line = line.replace('s', 'ch')
    g.write(line)

f.close()
g.close()