Search from end of file in python 3

Question

One of the changes in python 3 was the removal of the search capability from the end of the file in plain text mode. What is the generally accepted alternative to this?

For example, in python 2.7 I would enter the .seek file (-3,2)

I read a little why they did this, so please do not just contact PEP. I know that using "rb" would allow me to search, but it makes my text file read in the wrong format.

Answer 1

In Python 2, file data was not decoded while reading. Finding reverse and multibyte encodings doesn't mix well (you can't know where the next character will run), so it's disabled for Python 3.

You can still search for the underlying buffer object using the TextIOBase.buffer attribute, but then you will have to reconnect the new TextIOBase , since the current shell no longer knows where it is:

 import io file.buffer.seek(-3, 2) file = io.TextIOWrapper( file.buffer, encoding=file.encoding, errors=file.errors, newline=file.newlines) 

I copied any information about encoding and processing strings into an io.TextIOWrapper() object.

Note that this can decrypt decoding for UTF-16, UTF-32, UTF-8 and other multibyte codecs.

Demo:

 >>> import io >>> with open('demo.txt', 'w') as out: ... out.write('Demonstration\nfor seeking from the end') ... 38 >>> with open('demo.txt') as inf: ... print(inf.readline()) ... inf.buffer.seek(-3, 2) ... inf = io.TextIOWrapper(inf.buffer) ... print(inf.readline()) ... Demonstration 35 end 

You can wrap this in a utility function:

 import io def textio_seek(fobj, amount, whence=0): fobj.buffer.seek(amount, whence) return io.TextIOWrapper( fobj.buffer, encoding=fobj.encoding, errors=fobj.errors, newline=fobj.newlines) 

and use it like:

 with open(somefile) as file: # ... file = textio_seek(file, -2, 3) # ... 

Using the file object as a context manager still works because the original reference to the object object is still bound to the original file buffer object and, therefore, can be used to close the file.