Question

So I have a program which runs. This is part of the code:

FileName = 'Numberdata.dat'
NumberFile = open(FileName, 'r')
for Line in NumberFile:
  if Line == '4':
    print('1')
  else:
    print('9')
NumberFile.close()

A pretty pointless thing to do, yes, but I’m just doing it to enhance my understanding. However, this code doesn’t work. The file remains as it is and the 4’s are not replaced by 1’s and everything else isn’t replaced by 9’s, they merely stay the same. Where am I going wrong?

Numberdata.dat is "444666444666444888111000444"

It is now:

FileName = 'Binarydata.dat'
BinaryFile = open(FileName, 'w')
for character in BinaryFile:
  if charcter == '0':
    NumberFile.write('')
  else:
    NumberFile.write('@')
BinaryFile.close()

Answer 1

You need to build up a string and write it to the file.

FileName = 'Numberdata.dat'
NumberFileHandle = open(FileName, 'r')
newFileString = ""
for Line in NumberFileHandle:
  for char in line: # this will work for any number of lines.
      if char == '4':
        newFileString += "1"
      elif char == '\n':
        newFileString += char
      else:
        newFileString += "9"
NumberFileHandle.close()

NumberFileHandle = open(FileName, 'w')
NumberFileHandle.write(newFileString)
NumberFileHandle.close()