Delete final line in file with python

Question

How can one delete the very last line of a file with python?

Input File example:

hello world foo bar 

Output File example:

hello world foo 

I've created the following code to find the number of lines in the file - but I do not know how to delete the specific line number.

    try:         file = open("file")     except IOError:         print "Failed to read file."     countLines = len(file.readlines()) 

Answer 1

Because I routinely work with many-gigabyte files, looping through as mentioned in the answers didn't work for me. The solution I use:

with open(sys.argv[1], "r+", encoding = "utf-8") as file:      # Move the pointer (similar to a cursor in a text editor) to the end of the file     file.seek(0, os.SEEK_END)      # This code means the following code skips the very last character in the file -     # i.e. in the case the last line is null we delete the last line     # and the penultimate one     pos = file.tell() - 1      # Read each character in the file one at a time from the penultimate     # character going backwards, searching for a newline character     # If we find a new line, exit the search     while pos > 0 and file.read(1) != "\n":         pos -= 1         file.seek(pos, os.SEEK_SET)      # So long as we're not at the start of the file, delete all the characters ahead     # of this position     if pos > 0:         file.seek(pos, os.SEEK_SET)         file.truncate() 

Answer 2

You could use the above code and then:-

lines = file.readlines() lines = lines[:-1] 

This would give you an array of lines containing all lines but the last one.