In Python, there are multiple ways to read the last few lines of a file. Some are easy, convenient or efficient and some are not.
Small file
For small file, you can load the whole file into memory and access the last 5 lines using negative indices. Here is the example.
# Load the whole file into memory. with open("myfile.txt", "r") as file: lines=file.readlines() # Use negative indices to print last 5 lines. # Will display the last line, 2nd line from the end, # 3rd line from the end and so on. for i in range(1,6): print(lines[i*-1])
Big file
Obviously, for big file, you can't load the whole file into memory. Otherwise, you may run out of memory space. So, a better way would be to read through the file line by line and hold only the last 5 lines in a list until the end. Here is an example.
# Read line by line and hold the last 5 lines in last_lines list. with open("myfile.txt", "r") as file: i=0 lines_size = 5 last_lines = [] for line in file: if i < lines_size: last_lines.append(line) else: last_lines[i%lines_size] = line i = i + 1 # Shift the last line index to the end of list: # The last line index can be in the middle of the list. last_lines = last_lines[(i%lines_size):] + last_lines[:(i%lines_size)] # Display the last 5 lines. # Will display the 5th line from the end, 4th line from the end, # and so on. for line in last_lines: print(line)
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Xuan Ngo is the founder of OpenWritings.net. He currently lives in Montreal, Canada. He loves to write about programming and open source subjects.