CODEWITHSUNDEEP
pythonbinary
sidharth kumar
sidharth kumar

Reputation: 29

python replace string method in read file as binary

I opened an image file in readbinary("rb") mode and stored the data in a variable. Now i want to replace some values in the binary with my values.. but its not working using usual replace method of string

f=open("a.jpg","rb")
a=f.read()

''' first line is '\xff\xd8\xff\xe0\x00\x10JFIF\x00\x01\x01\x00\x00\x01\x00\x01\x00\x00\xff\xe1\x00*Exif\x00\x00II*\x00\x08\x00\x00\x00\x0 '''

a=a.replace("ff","z")
print a

#but there's no change in a

can anyone tell where iam going wrong.. i also tried

a=a.replace(b'ff',b'z')

but still the output was unchanged.

can anyone tell what iam supposed to do to perform the replacement?

Upvotes: 1

Views: 1524

Answers (2)

Mark Ransom
Mark Ransom

Reputation: 308148

When you display a string at the Python console, the string is encoded so that you can see all of the characters, even the ones that aren't printable. Whenever you see something like \xff, that's not 4 characters, it's a single character in hex notation. To replace it, you also need to specify the same single character.

a = a.replace("\xff", "z")

Upvotes: 0

erhesto
erhesto

Reputation: 1186

I don't know which version of Python you're using (this kind of operations are different between 2 and 3), but try a = str(a) before executing replace method.

EDIT: For python 2.7 only reasonable way I've discovered to do what you want is use built-in function repr. Example:

>>> picture = open("some_picture.jpg", 'rb')
>>> first_line = picture.readline()
>>> first_line
'\xff\xd8\xff\xe0\x00\x10JFIF\x00\x01\x01\x00\x00\x01\x00\x01\x00\x00\xff\xe1\x00*Exif\x00\x00II*\x00\x08\x00\x00\x00\x01\x001\x01\x02\x00\x07\x00\x00\x00\x1a\x00\x00\x00\x00\x00\x00\x00Google\x00\x00\xff\xdb\x00\x84\x00\x03\x02\x02\x03\x02\x02\x03\x03\x03\x03\x04\x03\x03\x04\x05\x08\x05\x05\x04\x04\x05\n'
>>> repr(first_line)
>>> "'\\xff\\xd8\\xff\\xe0\\x00\\x10JFIF\\x00\\x01\\x01\\x00\\x00\\x01\\x00\\x01\\x00\\x00\\xff\\xe1\\x00*Exif\\x00\\x00II*\\x00\\x08\\x00\\x00\\x00\\x01\\x001\\x01\\x02\\x00\\x07\\x00\\x00\\x00\\x1a\\x00\\x00\\x00\\x00\\x00\\x00\\x00Google\\x00\\x00\\xff\\xdb\\x00\\x84\\x00\\x03\\x02\\x02\\x03\\x02\\x02\\x03\\x03\\x03\\x03\\x04\\x03\\x03\\x04\\x05\\x08\\x05\\x05\\x04\\x04\\x05\\n'"
>>> repr(first_line).replace('ff', 'SOME_OTHER_STRING')
"'\\xSOME_OTHER_STRING\\xd8\\xSOME_OTHER_STRING\\xe0\\x00\\x10JFIF\\x00\\x01\\x01\\x00\\x00\\x01\\x00\\x01\\x00\\x00\\xSOME_OTHER_STRING\\xe1\\x00*Exif\\x00\\x00II*\\x00\\x08\\x00\\x00\\x00\\x01\\x001\\x01\\x02\\x00\\x07\\x00\\x00\\x00\\x1a\\x00\\x00\\x00\\x00\\x00\\x00\\x00Google\\x00\\x00\\xSOME_OTHER_STRING\\xdb\\x00\\x84\\x00\\x03\\x02\\x02\\x03\\x02\\x02\\x03\\x03\\x03\\x03\\x04\\x03\\x03\\x04\\x05\\x08\\x05\\x05\\x04\\x04\\x05\\n'"

Upvotes: 1

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