How to get the last character in a file from Python?

Question

I'm trying to set a variable to the last character of a file. I am using Python, and I'm fairly new to it. If it is of any importance, my code appends a random number between 2 and 9 to the end of an HTML file. In a separate function, I want to set the last character of the HTML file (the last character being the random number between 2 and 9) to a variable, then delete the last character (as to not affect the function of the HTML). Doe's anyone know how I could do this? I can attach my code below if needed, but I chose not to as it is 50 lines long and all 50 lines are needed for full context.

Answer 1

try this,

"a.txt" file has number 1, 3, 4, 5

Below code will read the file and pulls out last character from the file.

file = open('a.txt','r')  
lines = file.read()       
print(lines[-1])    

=> 5

Answer 2

Using @Jab's answer from the comment above as well as some assumptions, we can produce a more efficient solution to finding the last character and replacing it.

The assumptions that are made are common and most likely will be valid:

1. You will know whether there is a newline character at the very end of the file, or whether the random number is truly the last character in the file (meaning accounting for whitespace).
2. You know the encoding of the file. This is valid since almost all HTML is utf-8, (can be utf-16), and since you are the one editing it, you will know. Most times the encoding won't even matter.

So, this is what we can do:

with open("test.txt", "rb+", encoding='utf-8') as f:
    f.seek(-2, 2)
    # -1 or -2, may change depending on whitespace characters at end of the file
    var = f.read(1) # read one byte for a number 
    f.seek(-1,1)
    print("last character:", str(var, 'utf-8'))
    f.write(bytes('variable', 'utf-8')) # set whatever info here
    f.write(bytes('\n', 'utf-8')) # you may want a newline character at the end of the file
    f.truncate()

This is efficient because we actually don't have to iterate through the entire file. We iterate through just the last character, once to read and once to write.

Answer 3

You can do something like that:

# Open the file to read and the file to write
with open('file.txt'), open('new_file.txt', 'w+') as f_in, f_out:
    # Read all the lines to memory (you can't find the last line lazily)
    lines = f_in.readlines()

    # Iterate over every line
    for i, line in enumerate(lines):
        # If the current index is the last index (i.e. the last line)
        if i == len(lines) - 1:
            # Get the last character
            last_char = line[-1]

            # Write to the output file the line without the last character
            print(line[:-1], file=f_out, end='')

        else:
            # Write to the output file the line as it is
            print(line, file=f_out, end='')

# Print the removed char
print(last_char)    

If you don't want to create a new file, you can load all the file to memory as we're currently doing:

# Read all the lines into memory
with open('file.txt') as f:
    lines = f.readlines()

# Replace the lines inside the list using the previous logic
for i, line in enumerate(lines):
    if i == len(lines) - 1:
       last_char = line[-1]
       lines[i] = line[:-1]

    else:
       lines[i] = line

# Write the changed lines to the same file
with open('file.txt', 'w+') as f:
    print(''.join(lines), file=f, end='')

# Print the removed char
print(last_char)