File handling

Copying files - a simple and functional tool

Now you're going to amalgamate all this new knowledge, add some fresh elements to it, and use it to write a real code which is able to actually copy a file's contents.

Of course, the purpose is not to make a better replacement for commands like copy (MS Windows) or cp (Unix/Linux) but to see one possible way of creating a working tool, even if nobody wants to use it.

Look at the code in the editor. Let's analyze it:

• lines 3 through 8: ask the user for the name of the file to copy, and try to open it to read; terminate the program execution if the open fails; note: use the exit() function to stop program execution and to pass the completion code to the OS; any completion code other than 0 says that the program has encountered some problems; use the errno value to specify the nature of the issue;
• lines 10 through 16: repeat nearly the same action, but this time for the output file;
• line 18: prepare a piece of memory for transferring data from the source file to the target one; such a transfer area is often called a buffer, hence the name of the variable; the size of the buffer is arbitrary - in this case, we decided to use 64 kilobytes; technically, a larger buffer is faster at copying items, as a larger buffer means fewer I/O operations; actually, there is always a limit, the crossing of which renders no further improvements; test it yourself if you want.
• line 19: count the bytes copied - this is the counter and its initial value;
• line 21: try to fill the buffer for the very first time;
• line 22: as long as you get a non-zero number of bytes, repeat the same actions;
• line 23: write the buffer's contents to the output file (note: we've used a slice to limit the number of bytes being written, as write() always prefer to write the whole buffer)
• line 24: update the counter;
• line 25: read the next file chunk;
• lines 30 through 32: some final cleaning - the job is done.

from os import strerror srcname = "text.txt" try: src = open(srcname, 'rb') except IOError as e: print("Cannot open the source file: ", strerror(e.errno)) exit(e.errno) dstname = "ali.txt" try: dst = open(dstname, 'wb') except Exception as e: print("Cannot create the destination file: ", strerror(e.errno)) src.close() exit(e.errno) buffer = bytearray(5) total = 0 try: readin = src.readinto(buffer) #stores no.of bytes readinto buffer from file into readin variable while buffer is also updated print(buffer) print(readin) while readin > 0:#loop required in case our buffer is smaller than source file size\n written = dst.write(buffer[:readin])#slicing to write only the no of bytes written into buffer from src and not to write the 0's9if buffer is greater than source file or to continue from last pointer to no.of bytes readinto (if loop is run more than once) print(written) total += written print(f"total is {total}") readin = src.readinto(buffer)#gives 0 as pointer is at where we last read from but all content has been read print(buffer) print(f'readin is {readin}') except IOError as e: print("Cannot create the destination file: ", strerror(e.errno)) exit(e.errno) print(total,'byte(s) succesfully written') src.close() dst.close()